Ageing or aging (American English) is the accumulation of changes in a person over time. Ageing in humans refers to a multidimensional process of physical
Human body
The human body is the entire structure of a human organism, and consists of a head, neck, torso, two arms and two legs.By the time the human reaches adulthood, the body consists of close to 100 trillion cells, the basic unit of life...

, psychological, and social
The term social refers to a characteristic of living organisms...

 change. Some dimensions of ageing grow and expand over time, while others decline. Reaction time, for example, may slow with age, while knowledge of world events and wisdom may expand. Research shows that even late in life, potential exists for physical, mental, and social growth and development. Ageing is an important part of all human societies reflecting the biological changes that occur, but also reflecting cultural and societal conventions. Roughly 100,000 people worldwide die each day of age-related causes.

Age is measured chronologically, and a person's birthday
A birthday is a day or anniversary where a person celebrates his or her date of birth. Birthdays are celebrated in numerous cultures, often with a gift, party or rite of passage. Although the major religions celebrate the birth of their founders , Christmas – which is celebrated widely by...

 is often an important event. However the term "ageing" is somewhat ambiguous. Distinctions may be made between "universal ageing" (age changes that all people share) and "probabilistic ageing" (age changes that may happen to some, but not all people as they grow older including diseases such as type two diabetes
Diabetes mellitus type 2
Diabetes mellitus type 2formerly non-insulin-dependent diabetes mellitus or adult-onset diabetesis a metabolic disorder that is characterized by high blood glucose in the context of insulin resistance and relative insulin deficiency. Diabetes is often initially managed by increasing exercise and...

). Chronological ageing may also be distinguished from "social ageing" (cultural age-expectations of how people should act as they grow older) and "biological ageing" (an organism's physical state as it ages). There is also a distinction between "proximal ageing" (age-based effects that come about because of factors in the recent past) and "distal ageing" (age-based differences that can be traced back to a cause early in person's life, such as childhood poliomyelitis
Poliomyelitis, often called polio or infantile paralysis, is an acute viral infectious disease spread from person to person, primarily via the fecal-oral route...


Differences are sometimes made between populations of elderly people. Divisions are sometimes made between the young old (65–74), the middle old (75–84) and the oldest old (85+). However, problematic in this is that chronological age does not correlate perfectly with functional age, i.e. two people may be of the same age, but differ in their mental and physical capacities. Each nation, government and non-government organisation has different ways of classifying age.

Population ageing
Population ageing
Population ageing or population aging occurs when the median age of a country or region rises. This happens because of rising life expectancy or declining birth rates. Excepting 18 countries termed 'demographic outliers' by the UN) this process is taking place in every country and region across...

 is the increase in the number and proportion of older people in society. Population ageing has three possible causes: migration, longer life expectancy
Life expectancy
Life expectancy is the expected number of years of life remaining at a given age. It is denoted by ex, which means the average number of subsequent years of life for someone now aged x, according to a particular mortality experience...

 (decreased death rate), and decreased birth rate. Ageing has a significant impact on society. Young people tend to commit most crimes, they are more likely to push for political and social change, to develop and adopt new technologies, and to need education. Older people have different requirements from society and government as opposed to young people, and frequently differing values as well. Older people are also far more likely to vote, and in many countries the young are forbidden from voting. Thus, the aged have comparatively more political influence.

Recent scientific successes in rejuvenation and extending a lifespan of model animals (mice-2.5 |times, yeast -15 times, nematodes-10 times) and discovery of variety of species (including humans of advanced ages) having negligible senescence  give hope to achieve negligible senescence (cancel ageing) for younger humans, reverse ageing or at least significantly delay it.

Early observations

The first formal studies of ageing appear to be those of Muhammad ibn Yusuf al-Harawi
Muhammad ibn Yusuf al-Harawi
Muhammad ibn Yusuf al-Harawi was a Persian late 15th century physician from Herat, now part of Afghanistan.In 1518 he composed, in Arabic, an alphabetical medical dictionary and encyclopedia. It covered anatomical and pathological terms and concepts, medicinal substances, and prominent physicians,...

 (1582) in his book Ainul Hayat, published by Ibn Sina Academy of Medieval Medicine and Sciences
Ibn Sina Academy of Medieval Medicine and Sciences
Ibn Sina Academy of Medieval Medicine and Sciences is one of the Indian NGOs, which is registered under the Indian Trusts Act, 1882. Mohammad Hamid Ansari, former vice-chancellor of Aligarh Muslim University, Aligarh, formally inaugurated it on April 21, 2001...

. This book is based only on ageing and its related issues. The original manuscript of Ainul Hayat was scribed in 1532 by the author Muhammad ibn Yusuf al-Harawi. Four copies of the manuscript survive and were reprinted in an edited and translated version by Hakim Syed Zillur Rahman
Hakim Syed Zillur Rahman
Hakim Syed Zillur Rahman , is well known for his contribution to Unani medicine. He founded Ibn Sina Academy of Medieval Medicine and Sciences in 2000...

 (2007). The book discusses behavioural and lifestyle factors putatively influencing ageing including diet, environment and housing conditions. Also discussed are drugs that may increase and decrease ageing rates.


In biology, senescence
Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to those affecting the whole organism...

is the state or process of ageing. Cellular senescence is a phenomenon where isolated cells demonstrate a limited ability to divide in culture (the Hayflick Limit
Hayflick limit
The Hayflick limit is the number of times a normal cell population will divide before it stops, presumably because the telomeres reach a critical length....

, discovered by Leonard Hayflick in 1961), while organismal senescence is the ageing of organisms. After a period of near perfect renewal (in humans, between 20 and 35 years of age), organismal senescence is characterised by the declining ability to respond to stress, increasing homeostatic
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...

 imbalance and increased risk of disease. This currently irreversible series of changes inevitably ends in death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....

. Some researchers (specifically biogerontologists) are treating ageing as a disease. As genes that have an effect on ageing are discovered, ageing is increasingly being regarded in a similar fashion to other geneticly influenced "conditions", potentially "treatable."

Indeed, ageing is not an unavoidable property of life. Instead, it is the result of a genetic program. Numerous species show very low signs of ageing ("negligible senescence
Negligible senescence
Negligible senescence refers to the failure of a few select animals to display symptoms of aging. More specifically, negligibly senescent animals do not have measurable reductions in their reproductive capability with age, or measurable functional decline with age. Death rates in negligibly...

"), the best known being trees like the bristlecone pine
Bristlecone pine
The bristlecone pines are a small group of pine trees that are thought to reach an age far greater than that of any other single living organism known, up to nearly 5,000 years....

 (however Dr. Hayflick states that the bristlecone pine has no cells older than 30 years), fish like the sturgeon
Sturgeon is the common name used for some 26 species of fish in the family Acipenseridae, including the genera Acipenser, Huso, Scaphirhynchus and Pseudoscaphirhynchus. The term includes over 20 species commonly referred to as sturgeon and several closely related species that have distinct common...

 and the rockfish
Sebastes is a genus of fish in the family Sebastidae , most of which have the common name of rockfish. Most of the world's almost 110 Sebastes species live in the north Pacific, although two live in the south Pacific/Atlantic and four Sebastes is a genus of fish in the family Sebastidae (though...

, invertebrates like the quahog and sea anemone
Sea anemone
Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria; they are named after the anemone, a terrestrial flower. Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Zoantharia. Anthozoa often have large polyps that allow for digestion of larger...

 and lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...


In humans and other animals, cellular senescence
Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to those affecting the whole organism...

has been attributed to the shortening of telomere
A telomere is a region of repetitive DNA sequences at the end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes. Its name is derived from the Greek nouns telos "end" and merοs "part"...

s with each cell cycle
Cell cycle
The cell cycle, or cell-division cycle, is the series of events that takes place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission...

; when telomeres become too short, the cells die. The length of telomeres is therefore the "molecular clock," predicted by Hayflick.

Telomere length is maintained in immortal cells (e.g. germ cells and keratinocyte
Keratinocytes are the predominant cell type in the epidermis, the outermost layer of the human skin, constituting 95% of the cells found there. Those keratinocytes found in the basal layer of the skin are sometimes referred to as "basal cells" or "basal keratinocytes"...

 stem cells, but not other skin cell types) by the telomerase enzyme. In the laboratory, mortal cell lines can be immortalised by the activation of their telomerase gene, present in all cells but active in few cell types. Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

ous cells must become immortal to multiply without limit. This important step towards carcinogenesis implies, in 85% of cancers, the reactivation of their telomerase gene by mutation. Since this mutation is rare, the telomere "clock" can be seen as a protective mechanism against cancer. Research has shown that the clock must be located in the nucleus of each cell and there have been reports that the longevity clock might be located in genes on either the first or fourth chromosome of the twenty-three pairs of human chromosomes.

Other genes are known to affect the ageing process. The sirtuin
Sirtuin or Sir2 proteins are a class of proteins that possess either histone deacetylase or mono-ribosyltransferase activity. Sirtuins regulate important biological pathways in bacteria, archaea and eukaryotes...

 family of genes have been shown to have a significant effect on the lifespan of yeast
Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...

 and nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...

s. Over-expression of the RAS2 gene increases lifespan in yeast substantially.

In addition to genetic ties to lifespan, diet has been shown to substantially affect lifespan in many animals. Specifically, caloric restriction
Calorie restriction
Caloric restriction , or calorie restriction, is a dietary regimen that restricts calorie intake, where the baseline for the restriction varies, usually being the previous, unrestricted, intake of the subjects...

 (that is, restricting calories to 30-50% less than an ad libitum animal would consume, while still maintaining proper nutrient intake), has been shown to increase lifespan in mice up to 50%. Caloric restriction works on many other species beyond mice (including species as diverse as yeast and Drosophila), and appears (though the data is not conclusive) to increase lifespan in primates according to a study done on Rhesus monkeys at the National Institute of Health (US), although the increase in lifespan is only notable if the caloric restriction is started early in life. Since, at the molecular level, age is counted not as time but as the number of cell doublings, this effect of calorie reduction could be mediated by the slowing of cellular growth and, therefore, the lengthening of the time between cell divisions.

Drug companies are currently searching for ways to mimic the lifespan-extending effects of caloric restriction without having to severely reduce food consumption.

In his book, 'How and Why We Age', Dr. Hayflick notes a contradiction to the caloric restriction longevity increase theory for humans, noting that data from the Baltimore Longitudinal Study of Ageing show that being thin does not favour longevity.

Dividing the lifespan

An animal's life is often divided into various age ranges. However, because biological changes are slow-moving and can vary within one's own species, arbitrary dates are usually set to mark periods of life. The human divisions given below are not valid in all cultures:
  • Juvenile
    Minor (law)
    In law, a minor is a person under a certain age — the age of majority — which legally demarcates childhood from adulthood; the age depends upon jurisdiction and application, but is typically 18...

     [via infancy
    A newborn or baby is the very young offspring of a human or other mammal. A newborn is an infant who is within hours, days, or up to a few weeks from birth. In medical contexts, newborn or neonate refers to an infant in the first 28 days after birth...

    , childhood
    Childhood is the age span ranging from birth to adolescence. In developmental psychology, childhood is divided up into the developmental stages of toddlerhood , early childhood , middle childhood , and adolescence .- Age ranges of childhood :The term childhood is non-specific and can imply a...

    , preadolescence, adolescence
    Adolescence is a transitional stage of physical and mental human development generally occurring between puberty and legal adulthood , but largely characterized as beginning and ending with the teenage stage...

     (teenager)]: 0-19
  • Early adulthood: 20-39
  • Middle adulthood: 40-59
  • Late adulthood: 60+

Ages can also be divided by decade:

Term Age (years, inclusive)
Denarian 10 to 19
Vicenarian 20 to 29
Tricenarian 30 to 39
Quadragenarian 40 to 49
Quinquagenarian 50 to 59
Sexagenarian 60 to 69
Septuagenarian 70 to 79
Octogenarian 80 to 89
Nonagenarian 90 to 99
A centenarian is a person who is or lives beyond the age of 100 years. Because current average life expectancies across the world are less than 100, the term is invariably associated with longevity. Much rarer, a supercentenarian is a person who has lived to the age of 110 or more, something only...

100 to 109
A supercentenarian is someone who has reached the age of 110 years. This age is achieved by about one in a thousand centenarians....

110 and older

People from 13 to 19 years of age are also known as teens or teenagers. Tween
Tween (demographic)
A tween is a North American neologism that describes a person who is between the ages of 9 and 12 years old . The term is often described in popular media as referring to a pre-adolescent who is at the "in-between" stage in their development when they are considered "too old for toys, too young...

is an American neologism referring to someone between the ages of 8 and 14. The casual terms "twentysomething", "thirtysomething", etc. are also in use to describe people by decades of age.

Cultural variations

In some cultures (for example Serbian
The Serbs are a South Slavic ethnic group of the Balkans and southern Central Europe. Serbs are located mainly in Serbia, Montenegro and Bosnia and Herzegovina, and form a sizable minority in Croatia, the Republic of Macedonia and Slovenia. Likewise, Serbs are an officially recognized minority in...

) there are other ways to express age: by counting years with or without including current year. For example, it could be said about the same person that he is twenty years old or that he is in the twenty-first year of his life. In Russian the former expression is generally used, the latter one has restricted usage: it is used for age of a deceased person in obituaries and for the age of an adult when it is desired to show him/her older than he/she is. (Psychologically, a woman in her 20th year seems older than one who is 19 years old.)

Depending on cultural and personal philosophy, ageing can be seen as an undesirable phenomenon, reducing beauty and bringing one closer to death; or as an accumulation of wisdom, mark of survival, and a status worthy of respect. In some cases numerical age is important (whether good or bad), whereas others find the stage in life that one has reached (adulthood, independence, marriage, retirement, career success) to be more important.

East Asian age reckoning
East Asian age reckoning
East Asian age reckoning is a concept and practice that originated in China and is widely used by other cultures in East Asia, which share this traditional way of counting a person's age. Newborns start at one year old, and each passing of a Lunar New Year, rather than the birthday, adds one year...

 is different from that found in Western culture
Western culture
Western culture, sometimes equated with Western civilization or European civilization, refers to cultures of European origin and is used very broadly to refer to a heritage of social norms, ethical values, traditional customs, religious beliefs, political systems, and specific artifacts and...

. Traditional Chinese culture uses a different ageing method, called Xusui (虛歲) with respect to common ageing which is called Zhousui (周歲). In the Xusui method, people are born at age 1, not age 0, because conception is already considered to be the start of the life span, and another difference is the ageing day: Xusui grows up at the Spring Festival (aka. Chinese New Year's Day), while Shuo An grows up at one's birthday.


There are variations in many countries as to what age a person legally becomes an adult.

Most legal systems define a specific ages for when an individual is allowed or obliged to do particular activities. These ages include voting age
Voting age
A voting age is a minimum age established by law that a person must attain to be eligible to vote in a public election.The vast majority of countries in the world have established a voting age. Most governments consider that those of any age lower than the chosen threshold lack the necessary...

, drinking age
Legal drinking age
Laws about the legal drinking age cover a wide range of issues and behaviours, addressing when and where alcohol can be consumed. The minimum age alcohol can be legally consumed can be different to the age when it can be purchased. These laws vary among different countries and many laws have...

, age of consent
Age of consent
While the phrase age of consent typically does not appear in legal statutes, when used in relation to sexual activity, the age of consent is the minimum age at which a person is considered to be legally competent to consent to sexual acts. The European Union calls it the legal age for sexual...

, age of majority
Age of majority
The age of majority is the threshold of adulthood as it is conceptualized in law. It is the chronological moment when minors cease to legally be considered children and assume control over their persons, actions, and decisions, thereby terminating the legal control and legal responsibilities of...

, age of criminal responsibility, marriageable age
Marriageable age
Marriageable age is the age at which a person is allowed to marry, either as of right or subject to parental or other forms of consent. The age and other requirements vary between countries, but generally it is set at 18, although most jurisdictions allow marriage at slightly younger ages with...

, age of candidacy
Age of candidacy
Age of candidacy is the minimum age at which a person can legally qualify to hold certain elected government offices. In many cases, it also determines the age at which a person may be eligible to stand for an election or be granted ballot access....

, and mandatory retirement age
Mandatory retirement age
Mandatory retirement is the age at which persons who hold certain jobs or offices are required by industry custom or by law to leave their employment, or retire. Typically, mandatory retirement is justified by the argument that certain occupations are either too dangerous or require high levels of...

. Admission to a movie for instance, may depend on age according to a motion picture rating system
Motion picture rating system
A motion picture rating system is designated to classify films with regard to suitability for audiences in terms of issues such as sex, violence, substance abuse, profanity, impudence or other types of mature content...

. A bus fare might be discounted for the young or old.

Similarly in many countries in jurisprudence
Jurisprudence is the theory and philosophy of law. Scholars of jurisprudence, or legal theorists , hope to obtain a deeper understanding of the nature of law, of legal reasoning, legal systems and of legal institutions...

, the defence of infancy is a form of defence
Defense (legal)
In civil proceedings and criminal prosecutions under the common law, a defendant may raise a defense in an attempt to avoid criminal or civil liability...

 by which a defendant
A defendant or defender is any party who is required to answer the complaint of a plaintiff or pursuer in a civil lawsuit before a court, or any party who has been formally charged or accused of violating a criminal statute...

 argues that, at the time a law was broken, they were not liable for their actions, and thus should not be held liable for a crime
Crime is the breach of rules or laws for which some governing authority can ultimately prescribe a conviction...

. Many courts recognise that defendants who are considered to be juveniles may avoid criminal prosecution on account of their age, and in borderline cases the age of the offender is often held to be a mitigating circumstance.

Economics and marketing

The economics of ageing are also of great importance. Children and teenagers have little money of their own, but most of it is available for buying consumer goods. They also have considerable impact on how their parents spend money.

Young adults are an even more valuable cohort. They often have an income but few responsibilities such as a mortgage or children. They do not yet have set buying habits and are more open to new products.

The young are thus the central target of marketers. Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...

 is programmed to attract the range of 15 to 35 year olds. Mainstream
Mainstream is, generally, the common current thought of the majority. However, the mainstream is far from cohesive; rather the concept is often considered a cultural construct....

 movies are also built around appealing to the young.

Health care demand

Many societies in Western Europe and Japan have ageing populations. While the effects on society are complex, there is a concern about the impact on health care demand. The large number of suggestions in the literature for specific interventions to cope with the expected increase in demand for long-term care in ageing societies can be organised under four headings: improve system performance; redesign service delivery; support informal caregivers; and shift demographic parameters.

However, the annual growth in national health spending is not mainly due to increasing demand from ageing populations, but rather has been driven by rising incomes, costly new medical technology, a shortage of health care workers and informational asymmetries between providers and patients.

Even so, it has been estimated that population ageing only explains 0.2 percentage points of the annual growth rate in medical spending of 4.3 percent since 1970. In addition, certain reforms to Medicare decreased elderly spending on home health care by 12.5 percent per year between 1996 and 2000. This would suggest that the impact of ageing populations on health care costs is not inevitable.

Impact on prisons

As of July 2007, medical costs for a typical inmate in the United States might run an agency around $33 per day, while costs for an ageing inmate could run upwards of $100. Most State DOCs
Department of Corrections
A Department of Corrections is a governmental agency responsible for overseeing the incarceration of persons convicted of crimes within a particular jurisdiction. Entities serving that purpose include:* Department of Corrections...

 report spending more than 10 percent of the annual budget on elderly care. That is expected to rise over the next 10–20 years. Some states have talked about releasing ageing inmates early.

Cognitive effects

Steady decline in many cognitive processes is seen across the lifespan, accelerating from the thirties. Research has focused in particular on memory and ageing, and has found decline in many types of memory with ageing, but not in semantic memory
Semantic memory
Semantic memory refers to the memory of meanings, understandings, and other concept-based knowledge unrelated to specific experiences. The conscious recollection of factual information and general knowledge about the world is generally thought to be independent of context and personal relevance...

 or general knowledge such as vocabulary definitions, which typically increases or remains steady. Early studies on changes in cognition with age generally found declines in intelligence in the elderly, but studies were cross-sectional
Cross-sectional study
Cross-sectional studies form a class of research methods that involve observation of all of a population, or a representative subset, at one specific point in time...

 rather than longitudinal
Longitudinal study
A longitudinal study is a correlational research study that involves repeated observations of the same variables over long periods of time — often many decades. It is a type of observational study. Longitudinal studies are often used in psychology to study developmental trends across the...

 and thus results may be an artefact of cohort
Cohort (statistics)
In statistics and demography, a cohort is a group of subjects who have shared a particular time together during a particular time span . Cohorts may be tracked over extended periods in a cohort study. The cohort can be modified by censoring, i.e...

 rather than a true example of decline. Intelligence
Intelligence has been defined in different ways, including the abilities for abstract thought, understanding, communication, reasoning, learning, planning, emotional intelligence and problem solving....

 may decline with age, though the rate may vary depending on the type
Theory of multiple intelligences
The theory of multiple intelligences was proposed by Howard Gardner in 1983 as a model of intelligence that differentiates intelligence into various specific modalities, rather than seeing it as dominated by a single general ability....

, and may in fact remain steady throughout most of the lifespan, dropping suddenly only as people near the end of their lives. Individual variations in rate of cognitive decline may therefore be explained in terms of people having different lengths of life. There are changes to the brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...

: though neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

 loss is minor after 20 years of age there is a 10% reduction each decade in the total length of the brain's myelinated axons.

Coping and well-being

Psychology is the study of the mind and behavior. Its immediate goal is to understand individuals and groups by both establishing general principles and researching specific cases. For many, the ultimate goal of psychology is to benefit society...

 have examined coping skills in the elderly. Various factors, such as social support
Social support
Social support can be defined and measured in many ways. It can loosely be defined as feeling that one is cared for by and has assistance available from other people and that one is part of a supportive social network...

, religion and spirituality
Spirituality can refer to an ultimate or an alleged immaterial reality; an inner path enabling a person to discover the essence of his/her being; or the “deepest values and meanings by which people live.” Spiritual practices, including meditation, prayer and contemplation, are intended to develop...

, active engagement with life and having an internal locus of control
Locus of control
Locus of control is a theory in personality psychology referring to the extent to which individuals believe that they can control events that affect them. Understanding of the concept was developed by Julian B...

 have been proposed as being beneficial in helping people to cope with stressful life events in later life. Social support and personal control are possibly the two most important factors that predict well-being, morbidity and mortality in adults. Other factors that may link to well-being and quality of life
Quality of life
The term quality of life is used to evaluate the general well-being of individuals and societies. The term is used in a wide range of contexts, including the fields of international development, healthcare, and politics. Quality of life should not be confused with the concept of standard of...

 in the elderly include social relationships (possibly relationships with pets as well as humans), and health
Health is the level of functional or metabolic efficiency of a living being. In humans, it is the general condition of a person's mind, body and spirit, usually meaning to be free from illness, injury or pain...


Individuals in different wings in the same retirement home
Retirement home
A retirement home is a multi-residence housing facility intended for senior citizens. Typically each person or couple in the home has an apartment-style room or suite of rooms. Additional facilities are provided within the building, including facilities for meals, gathering, recreation, and some...

 have demonstrated a lower risk of mortality and higher alertness and self-rated health in the wing where residents had greater control over their environment, though personal control may have less impact on specific measures of health. Social control, perceptions of how much influence one has over one's social relationships, shows support as a moderator variable for the relationship between social support and perceived health in the elderly, and may positively influence coping in the elderly.


Religion has been an important factor used by the elderly in coping with the demands of later life, and appears more often than other forms of coping later in life. Religious commitment may also be associated with reduced mortality, though religiosity
Religiosity, in its broadest sense, is a comprehensive sociological term used to refer to the numerous aspects of religious activity, dedication, and belief . Another term that would work equally well, though is less often used, is religiousness...

 is a multidimensional variable; while participation in religious activities in the sense of participation in formal and organised ritual
A ritual is a set of actions, performed mainly for their symbolic value. It may be prescribed by a religion or by the traditions of a community. The term usually excludes actions which are arbitrarily chosen by the performers....

s may decline, it may become a more informal, but still important aspect of life such as through personal or private prayer
Prayer is a form of religious practice that seeks to activate a volitional rapport to a deity through deliberate practice. Prayer may be either individual or communal and take place in public or in private. It may involve the use of words or song. When language is used, prayer may take the form of...


Self-rated health

Self-ratings of health, the beliefs in one's own health as excellent, fair or poor, has been correlated with well-being and mortality in the elderly; positive ratings are linked to high well-being and reduced mortality. Various reasons have been proposed for this association; people who are objectively healthy may naturally rate their health better than that of their ill counterparts, though this link has been observed even in studies which have controlled for socioeconomic status
Socioeconomic status
Socioeconomic status is an economic and sociological combined total measure of a person's work experience and of an individual's or family’s economic and social position in relation to others, based on income, education, and occupation...

, psychological functioning and health status. This finding is generally stronger for men than women, though the pattern between genders is not universal across all studies, and some results suggest sex-based differences only appear in certain age groups, for certain causes of mortality and within a specific sub-set of self-ratings of health.


Retirement is the point where a person stops employment completely. A person may also semi-retire by reducing work hours.Many people choose to retire when they are eligible for private or public pension benefits, although some are forced to retire when physical conditions don't allow the person to...

, a common transition faced by the elderly, may have both positive and negative consequences.

Societal impact

Of the roughly 150,000 people who die each day across the globe, about two thirds — 100,000 per day — die of age-related causes. In industrialised nations, the proportion is much higher, reaching 90%.

Societal ageing refers to the demographic ageing of populations and societies. Cultural differences in attitudes to ageing have been studied.

Emotional improvement

Given the physical and cognitive declines seen in ageing, a surprising finding is that emotional experience improves with age. Older adults are better at regulating their emotions and experience negative affect less frequently than younger adults and show a positivity effect
Positivity effect
In psychology and cognitive science, the positivity effect is the tendency of people, when evaluating the causes of the behaviors of a person they like or prefer, to attribute the person's inherent disposition as the cause of their positive behaviors and the situations surrounding them as the cause...

 in their attention and memory. The emotional improvements show up in longitudinal studies as well as in cross-sectional studies and so cannot be entirely due to only the happier individuals surviving.

Successful ageing

The concept of successful ageing can be traced back to the 1950s, and popularised in the 1980s. Previous research into ageing exaggerated the extent to which health disabilities, such as diabetes or osteoporosis
Osteoporosis is a disease of bones that leads to an increased risk of fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is deteriorating, and the amount and variety of proteins in bone is altered...

, could be attributed exclusively to age, and research in gerontology
Gerontology is the study of the social, psychological and biological aspects of aging...

 exaggerated the homogeneity of samples of elderly people.

Successful ageing consists of three components:
  1. Low probability of disease or disability;
  2. High cognitive and physical function capacity;
  3. Active engagement with life.

A greater number of people self-report successful ageing than those that strictly meet these criteria.

Successful ageing may be viewed an interdisciplinary concept, spanning both psychology
Psychology is the study of the mind and behavior. Its immediate goal is to understand individuals and groups by both establishing general principles and researching specific cases. For many, the ultimate goal of psychology is to benefit society...

 and sociology
Sociology is the study of society. It is a social science—a term with which it is sometimes synonymous—which uses various methods of empirical investigation and critical analysis to develop a body of knowledge about human social activity...

, where it is seen as the transaction between society and individuals across the life span with specific focus on the later years of life. The terms "healthy ageing" "optimal ageing" have been proposed as alternatives to successful ageing.

Six suggested dimensions of successful ageing include:
  1. No physical disability over the age of 75 as rated by a physician;
  2. Good subjective health assessment (i.e. good self-ratings of one's health);
  3. Length of undisabled life;
  4. Good mental health
    Mental health
    Mental health describes either a level of cognitive or emotional well-being or an absence of a mental disorder. From perspectives of the discipline of positive psychology or holism mental health may include an individual's ability to enjoy life and procure a balance between life activities and...

  5. Objective social support
    Social support
    Social support can be defined and measured in many ways. It can loosely be defined as feeling that one is cared for by and has assistance available from other people and that one is part of a supportive social network...

  6. Self-rated life satisfaction in eight domains, namely marriage
    Marriage is a social union or legal contract between people that creates kinship. It is an institution in which interpersonal relationships, usually intimate and sexual, are acknowledged in a variety of ways, depending on the culture or subculture in which it is found...

    , income-related work, children, friendship and social contacts, hobbies, community service activities, religion and recreation/sports.

Biological theories

At present, the biological basis of ageing is unknown. Most scientists agree that substantial variability exists in the rates of ageing across different species, and that this to a large extent is genetically based. In model organisms and laboratory settings, researchers have been able to demonstrate that selected alterations in specific genes can extend lifespan (quite substantially in nematodes, less so in fruit flies, and less again in mice). Even in the relatively simple and short-lived organisms, the mechanism of ageing remain to be elucidated. Less is known about mammalian ageing, in part due to the much longer lives in even small mammals such as the mouse
A mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles...

 (around 3 years).

The US National Institute on Aging
National Institute on Aging
The National Institute on Aging ' is a division of the U.S. National Institutes of Health , located in Baltimore, Maryland.The NIA leads a broad scientific effort to understand the nature of aging and to extend the healthy, active years of life...

 currently funds an intervention testing program, whereby investigators nominate compounds (based on specific molecular ageing theories) to have evaluated with respect to their effects on lifespan and age-related biomarkers in outbred mice. Previous age-related testing in mammals has proved largely irreproducible, because of small numbers of animals, and lax mouse husbandry conditions. The intervention testing program aims to address this by conducting parallel experiments at three internationally recognised mouse ageing-centres, the Barshop Institute
Barshop Institute
The Barshop Institute for Longevity and Aging Studies is a basic and clinical research institute located on the Texas Research Park Campus of the University of Texas Health Science Center at San Antonio . It is a leading institute in the United States in geriatrics research...

 at UTHSCSA, the University of Michigan
University of Michigan
The University of Michigan is a public research university located in Ann Arbor, Michigan in the United States. It is the state's oldest university and the flagship campus of the University of Michigan...

 at Ann Arbor and the Jackson Laboratory
Jackson Laboratory
The Jackson Laboratory was founded in Bar Harbor, Maine in 1929 by former University of Maine and University of Michigan president C. C. Little under the name Roscoe B...


Many have argued that life-span, like other phenotypes, is selected
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....

  • Evolutionary Theories
    Evolution of ageing
    Enquiry into the evolution of ageing aims to explain why almost all living things weaken and die with age. There is not yet agreement in the scientific community on a single answer...

    : Enquiry into the evolution of ageing aims to explain why almost all living things weaken and die with age. Exceptions such as rockfish
    Sebastes is a genus of fish in the family Sebastidae , most of which have the common name of rockfish. Most of the world's almost 110 Sebastes species live in the north Pacific, although two live in the south Pacific/Atlantic and four Sebastes is a genus of fish in the family Sebastidae (though...

    , turtle
    Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...

    s, and naked molerat are highly informative.
  • Telomere Theory: Telomeres (structures at the ends of chromosomes) have experimentally been shown to shorten with each successive cell division.. Shortened telomeres activate a mechanism that prevents further cell multiplication . This may be particularly limit in tissues such as bone marrow and the arterial lining where cell division occurs repeatedly throughout life . Importantly though, mice lacking telomerase enzyme do not show a dramatically reduced lifespan , invalidating at least simple versions of the telomere theory of ageing. Mice may be an exception for the theory, as they have long hypervariable telomeres , prolonging the period after which telomere shortening would affect life-span. But wild mouse strains do not, and telomere length in these breeds is unrelated to lifespan

  • Reproductive-Cell Cycle Theory
    Reproductive-cell cycle theory
    Rather than seeing aging as a loss of functionality as we get older, this theory defines aging as any change in an organism over time, as evidenced by the fact that if all chemical reactions in the body were stopped, no change, and thus no aging, would occur...

    : The idea that ageing is regulated by reproductive hormones that act in an antagonistic pleiotropic manner via cell cycle signalling, promoting growth and development early in life in order to achieve reproduction, but later in life, in a futile attempt to maintain reproduction, become dysregulated and drive senescence (dyosis).

Some theories suggest that ageing is a disease. Two examples are
  • DNA
    Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

     Damage Theory of Ageing: Known causes of cancer
    Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

     (radiation, chemical and viral) account for about 30% of the total cancer burden and for about 30% of the total DNA damage. DNA damage causes the cells to stop dividing or induce apoptosis
    Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...

    , often affecting stem cell pools and hence hindering regeneration. DNA damage is thought to be the common pathway causing both cancer and ageing. It seems unlikely that the estimates of the DNA damage due to radiation and chemical causes has been significantly underestimated. Viral infection would appear to be the most likely cause of the other 70% of DNA damage especially in cells that are not exposed to smoking and sun light. It has been argued, too, that intrinsic causes of DNA damage are more important drivers of ageing.
  • Autoimmune Theory: The idea that ageing results from an increase in autoantibodies that attack the body's tissues. A number of diseases associated with ageing, such as atrophic gastritis
    Atrophic gastritis
    Atrophic gastritis is a process of chronic inflammation of the stomach mucosa, leading to loss of gastric glandular cells and their eventual replacement by intestinal and fibrous tissues...

     and Hashimoto's thyroiditis
    Hashimoto's thyroiditis
    Hashimoto's thyroiditis or chronic lymphocytic thyroiditis is an autoimmune disease in which the thyroid gland is gradually destroyed by a variety of cell- and antibody-mediated immune processes. It was the first disease to be recognized as an autoimmune disease...

    , are probably autoimmune in this way. While inflammation is very much evident in old mammals, even SCID
    Severe combined immunodeficiency
    Severe combined immunodeficiency , is a genetic disorder in which both "arms" of the adaptive immune system are impaired due to a defect in one of several possible genes. SCID is a severe form of heritable immunodeficiency...

     mice in SPF colonies still experience senescence.

Genetic theories

Many theories suggest that ageing results from the accumulation of damage to DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 in the cell, or organ. Since DNA is the formative basis of cell structure and function, damage to the DNA molecule, or genes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...

, can lead to its loss of integrity and early cell death.

Examples include:
  • Accumulative-Waste Theory: The biological theory of ageing that points to a buildup of cells of waste products that presumably interferes with metabolism.
  • Wear-and-Tear Theory: The very general idea that changes associated with ageing are the result of chance damage that accumulates over time.
  • Somatic Mutation Theory: The biological theory that ageing results from damage to the genetic integrity of the body’s cells.
  • Error Accumulation Theory: The idea that ageing results from chance events that escape proof reading mechanisms, which gradually damages the genetic code.

Some have argued that ageing is programmed: that an internal clock detects a time to end investing in the organism, leading to death. This ageing-Clock Theory suggests, as in a clock, an ageing sequence is built into the operation of the nervous or endocrine system of the body. In rapidly dividing cells the shortening of the telomeres would provide such a clock. This idea is in contradiction with the evolutionary based theory of ageing.
  • Cross-Linkage Theory: The idea that ageing results from accumulation of cross-linked compounds that interfere with normal cell function.
  • Free-Radical Theory
    Free-radical theory
    The free-radical theory of aging states that organisms age because cells accumulate free radical damage over time. A free radical is any atom or molecule that has a single unpaired electron in an outer shell. While a few free radicals such as melanin are not chemically reactive, most...

    : The idea that free radicals (unstable and highly reactive organic molecules), or more generally reactive oxygen species
    Reactive oxygen species
    Reactive oxygen species are chemically reactive molecules containing oxygen. Examples include oxygen ions and peroxides. Reactive oxygen species are highly reactive due to the presence of unpaired valence shell electrons....

     or oxidative stress
    Oxidative stress
    Oxidative stress represents an imbalance between the production and manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage...

     create damage that gives rise to symptoms we recognise as ageing.
  • Reliability theory of ageing and longevity: A general theory about systems failure. It allows researchers to predict the age-related failure kinetics for a system of given architecture (reliability structure) and given reliability of its components. Reliability theory predicts that even those systems that are entirely composed of non-ageing elements (with a constant failure rate) will nevertheless deteriorate (fail more often) with age, if these systems are redundant in irreplaceable elements. Ageing, therefore, is a direct consequence of systems redundancy. Reliability theory also predicts the late-life mortality deceleration with subsequent levelling-off, as well as the late-life mortality plateaus, as an inevitable consequence of redundancy exhaustion at extreme old ages. The theory explains why mortality rates increase exponentially with age (the Gompertz law) in many species, by taking into account the initial flaws (defects) in newly formed systems. It also explains why organisms "prefer" to die according to the Gompertz law, while technical devices usually fail according to the Weibull (power) law. Reliability theory allows to specify conditions when organisms die according to the Weibull distribution: organisms should be relatively free of initial flaws and defects. The theory makes it possible to find a general failure law applicable to all adult and extreme old ages, where the Gompertz and the Weibull laws are just special cases of this more general failure law. The theory explains why relative differences in mortality rates of compared populations (within a given species) vanish with age (compensation law of mortality
    Compensation law of mortality
    The compensation law of mortality states that the relative differences in death rates between different populations of the same biological species decrease with age, because the higher initial death rates in disadvantaged populations are compensated by lower pace of mortality increase with age...

    ), and mortality convergence is observed due to the exhaustion of initial differences in redundancy levels.
  • Mitohormesis: It has been known since the 1930s that restricting calories while maintaining adequate amounts of other nutrients can extend lifespan in laboratory animals. Recently, Michael Ristow
    Michael Ristow
    Michael Ristow is a German medical researcher who has published influential articles on the metabolic basis of human diseases, including type 2 diabetes, obesity and cancer, as well as general aging processes...

    's group has provided evidence for the theory that this effect is due to increased formation of free radicals within the mitochondria causing a secondary induction of increased antioxidant
    An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...

     defence capacity.
  • Misrepair-Accumulation Theory: Wang et al. suggest that ageing is the result of the accumulation of "Misrepair". Important in this theory is to distinguish among "damage" which means a newly emerging defect BEFORE any reparation has taken place, and "Misrepair" which describes the remaining defective structure AFTER (incorrect) repair. The key points in this theory are:
  1. There is no original damage left unrepaired in a living being. If damage was left unrepaired a life threatening condition (such as bleeding, infection, or organ failure) would develop.
  2. Misrepair, the repair with less accuracy, does not happen accidentally. It is a necessary measure of the reparation system to achieve sufficiently quick reparation in situations of serious or repeated damage, to maintain the integrity and basic function of a structure, which is important for the survival of the living being.
  3. Hence the appearance of Misrepair increases the chance for the survival of individual, by which the individual can live at least up to the reproduction age, which is critically important for the survival of species. Therefore the Misrepair mechanism was selected by nature due to its evolutionary advantage.
  4. However, since Misrepair as a defective structure is invisible for the reparation system, it accumulates with time and causes gradually the disorganisation of a structure (tissue, cell, or molecule); this is the actual source of ageing.
  5. Ageing hence is the side-effect for survival, but important for species survival. Thus Misrepair might represent the mechanism by which organisms are not programmed to die but to survive (as long as possible), and ageing is just the price to be paid.

Non-biological theories

Disengagement Theory
Disengagement theory
The disengagement theory of aging states that "aging is an inevitable, mutual withdrawal or disengagement, resulting in decreased interaction between the aging person and others in the social system he belongs to". The theory claims that it is natural and acceptable for older adults to withdraw...

: This is the idea that separation of older people from active roles in society is normal and appropriate, and benefits both society and older individuals. Disengagement theory, first proposed by Cumming and Henry, has received considerable attention in gerontology
Gerontology is the study of the social, psychological and biological aspects of aging...

, but has been much criticised. The original data on which Cumming and Henry based the theory were from a rather small sample of older adults in Kansas City, and from this select sample Cumming and Henry then took disengagement to be a universal theory. There are research data suggesting that the elderly who do become detached from society as those were initially reclusive individuals, and such disengagement is not purely a response to ageing.

Activity theory
Activity theory (aging)
The activity theory, also known as the implicit theory of aging, normal theory of aging, and lay theory of aging, proposes that successful aging occurs when older adults stay active and maintain social interactions....

: In contrast to disengagement theory, this theory implies that the more active elderly people are, the more likely they are to be satisfied with life. The view that elderly adults should maintain well-being by keeping active has had a considerable history, and since 1972, this has come to be known as activity theory. However, this theory may be just as inappropriate as disengagement for some people as the current paradigm on the psychology of ageing is that both disengagement theory and activity theory may be optimal for certain people in old age, depending on both circumstances and personality traits of the individual concerned. There are also data which query whether, as activity theory implies, greater social activity is linked with well-being in adulthood.

Selectivity Theory: mediates between Activity and Disengagement Theory, which suggests that it may benefit older people to become more active in some aspects of their lives, more disengaged in others.

Continuity Theory: The view that in ageing people are inclined to maintain, as much as they can, the same habits, personalities, and styles of life that they have developed in earlier years. Continuity theory is Atchley's theory that individuals, in later life, make adaptations to enable them to gain a sense of continuity between the past and the present, and the theory implies that this sense of continuity helps to contribute to well-being in later life. Disengagement theory, activity theory and continuity theory are social theories about ageing, though all may be products of their era rather than a valid, universal theory.

Prevention and reversal

Several drugs and food supplements have been shown to retard or reverse the biological effects of ageing in animal models; none has yet been proven to do so in humans.
Resveratrol is a stilbenoid, a type of natural phenol, and a phytoalexin produced naturally by several plants when under attack by pathogens such as bacteria or fungi....

, a chemical found in red grapes, has been shown to extend the lifespan of yeast by 60%, worms and flies by 30% and one species of fish by almost 60%. It does not extend the lifespan of healthy mice but delays the onset of age-related disease and infirmity.

Small doses of heavy water
Heavy water
Heavy water is water highly enriched in the hydrogen isotope deuterium; e.g., heavy water used in CANDU reactors is 99.75% enriched by hydrogen atom-fraction...

 increase fruit-fly lifespan by 30%, but large doses are toxic to complex organisms.

In 2002, a team led by Professor Bruce Ames
Bruce Ames
Bruce Nathan Ames is an American biochemist. He is a professor of Biochemistry and Molecular Biology at the University of California, Berkeley, and a senior scientist at Children's Hospital Oakland Research Institute...

 at UC Berkeley discovered that feeding aged rats a combination of acetyl-L-carnitine and alpha-lipoic acid (both substances are already approved for human use and sold in health food store
Health food store
A health food store is a type of grocery store that primarily sells health food, organic foods, local produce, and often nutritional supplements...

s) produced a rejuvenating effect. Ames said, "With these two supplements together, these old rats got up and did the macarena. The brain looks better, they are full of energy - everything we looked at looks like a young animal." UC Berkeley has patented the use of these supplements in combination and a company, Juvenon, has been established to market the treatment.

In 2007, researchers at the Salk Institute for Biological Studies
Salk Institute for Biological Studies
The Salk Institute for Biological Studies is a premier independent, non-profit, scientific research institute located in La Jolla, California. It was founded in 1960 by Jonas Salk, the developer of the polio vaccine; among the founding consultants were Jacob Bronowski and Francis Crick. Building...

, identified a critical gene in nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...

 worms that specifically links eating fewer calories with living longer. Professor Andrew Dillin and colleagues showed that the gene pha-4 regulates the longevity response to calorie restriction. In the same year Dr Howard Chang of the Stanford University School of Medicine
Stanford University School of Medicine
Stanford University School of Medicine is a leading medical school located at Stanford University Medical Center in Stanford, California. Originally based in San Francisco, California as Cooper Medical College, it is the oldest continuously running medical school in the western United States...

 was able to rejuvenate the skin of two-year-old mice to resemble that of newborns by blocking the activity of the gene NF-kappa-B.

In 2008, a team at the Spanish National Cancer Research Center genetically engineered mice to produce ten times the normal level of the telomerase enzyme. The mice lived 26% longer than normal. The same year a team led by Professor Michael O Thorner at the University of Virginia
University of Virginia
The University of Virginia is a public research university located in Charlottesville, Virginia, United States, founded by Thomas Jefferson...

 discovered that the drug MK-677
MK-677 is a drug which acts as a potent, orally active growth hormone secretagogue, mimicking the GH stimulating action of the endogenous hormone ghrelin. It has been demonstrated to increase the release of, and produces sustained increases in plasma levels of several hormones including growth...

 restored 20% of muscle mass lost due to ageing in humans aged 60 to 81. The subjects' growth hormone and insulin-like growth factor 1 (IGF-1) levels increased to that typical of healthy young adults.

In 2009, a drug called rapamycin, discovered in the 1970s in the soil of Easter Island
Easter Island
Easter Island is a Polynesian island in the southeastern Pacific Ocean, at the southeasternmost point of the Polynesian triangle. A special territory of Chile that was annexed in 1888, Easter Island is famous for its 887 extant monumental statues, called moai, created by the early Rapanui people...

 in the South Pacific, was found to extend the life expectancy of 20-month-old mice by up to 38%. Rapamycin is generally used to suppress the immune system and prevent the rejection of transplanted organs. Dr Arlan Richardson of the Barshop Institute said, "I never thought we would find an anti-ageing pill in my lifetime; however, rapamycin shows a great deal of promise to do just that." Professor Randy Strong of the University of Texas Health Science Center at San Antonio
University of Texas Health Science Center at San Antonio
The University of Texas Health Science Center at San Antonio is an institute of health science education and research, located in the South Texas Medical Center....

 said, "We believe this is the first convincing evidence that the ageing process can be slowed and lifespan can be extended by a drug therapy starting at an advanced age."

Also in 2009, the British Journal of Nutrition reported a study at Tufts University in Boston which showed that brain function and motor skills in aged rats could be improved by adding walnuts to their diet. The human equivalent would be to eat seven to nine walnuts per day.

In September 2009, researchers at UC Berkeley discovered they could restore youthful repair capability to muscle tissue taken from men aged 68 to 74 by in vitro treatment with mitogen-activated protein kinase. This protein was found to be essential for the production of the stem cells necessary to repair muscle after exercise and is present at reduced levels in aged individuals.

Ronald A. DePinho
Ronald A. DePinho
Ronald A. DePinho, M.D., president of The University of Texas MD Anderson Cancer Center in Houston, is internationally recognized for basic and translational research in cancer, aging and age-associated degenerative disorders....

, a cancer geneticist at the Dana-Farber Cancer Institute
Dana-Farber Cancer Institute
Dana–Farber Cancer Institute is part of a Comprehensive Cancer Center designated by the National Cancer Institute. It is a major affiliate of Harvard Medical School and is located in the Longwood Medical Area in Boston, Massachusetts.-Overview:...

 and Harvard Medical School
Harvard Medical School
Harvard Medical School is the graduate medical school of Harvard University. It is located in the Longwood Medical Area of the Mission Hill neighborhood of Boston, Massachusetts....

, published a paper in Nature magazine in November 2010 which indicated that the organs of genetically altered mice, designed to activate telomerase
Telomerase is an enzyme that adds DNA sequence repeats to the 3' end of DNA strands in the telomere regions, which are found at the ends of eukaryotic chromosomes. This region of repeated nucleotide called telomeres contains non-coding DNA material and prevents constant loss of important DNA from...

 after feeding them with a chemical, were rejuvenated.

Shrivelled testes grew back to normal and the animals regained their fertility. Other organs, such as the spleen, liver, intestines and brain, recuperated from their degenerated state. Dr Lynne Cox of Oxford University said, "This paper is extremely important as it provides proof of the principle that short-term treatment to restore telomerase in adults already showing age-related tissue degeneration can rejuvenate aged tissues and restore physiological function."

In this experiment mice were engineered to not produce telomerase naturally but after a chemical "switch" the system would then restore telomerase. Importantly, this chemical does not have the ability to produce telomerase in animals that are not genetically altered. Moreover, telomerase activation is also associated with the growth of cancerous tumours which could prevent anti-ageing treatments using this discovery.

Measure of age

The age of an adult human is commonly measured in whole years since the day of birth. Fractional years, months or even weeks may be used to describe the age of children and infants for finer resolution. The time of day the birth occurred is not commonly considered.

The measure of age has historically varied from this approach in some cultures. In parts of Tibet, age is counted from conception i.e. one is usually 9 months old when one is born.

Age in prenatal development is normally measured in gestational age
Gestational age
Gestational age relates to the age of an embryo or fetus . There is some ambiguity in how it is defined:*In embryology, gestational age is the time elapsed since conception. This interval is also termed fertilisation age....

, taking the last menstruation
Menstruation is the shedding of the uterine lining . It occurs on a regular basis in sexually reproductive-age females of certain mammal species. This article focuses on human menstruation.-Overview:...

 of the woman as a point of beginning. Alternatively, fertilisation age, beginning from fertilisation
Fertilisation is the fusion of gametes to produce a new organism. In animals, the process involves the fusion of an ovum with a sperm, which eventually leads to the development of an embryo...

can be taken.

Obtaining survey data on ageing

Numerous worldwide health, ageing and retirement surveys contain questions pertaining to pensions. The Meta Data Repository - created by the non-profit RAND Corporation and sponsored by the National Institute on Aging at the National Institutes of Health - provides access to meta data for these questions as well as links to obtain respondent data from the originating surveys.
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