Health and intelligence
Encyclopedia
Health
can affect intelligence
in various ways. This is one of the most important factors in understanding the origins of human group differences in IQ test scores and other measures of cognitive ability. Several factors can lead to significant cognitive impairment, particularly if they occur during pregnancy and childhood when the brain is growing and the blood-brain barrier
is less effective. Such impairment may sometimes be permanent, sometimes be partially or wholly compensated for by later growth.
Developed nations have implemented several health policies regarding nutrients and toxins known to influence cognitive function. These include laws requiring fortification
of certain food products and laws establishing safe levels of pollutants (e.g. lead
, mercury
, and organochloride
s). Comprehensive policy recommendations targeting reduction of cognitive impairment in children have been proposed.
Improvements in nutrition
, and in public policy in general, have been implicated in worldwide IQ increases (the Flynn effect
) .
, during breastfeeding
, infancy, or childhood. It may also happen due to deficiencies of different nutrients, such as micronutrients, protein
or energy. This may cause different effects.
during the first six months of life harms cognitive development much more than malnutrition later in life. However, a study from the Philippines
argues that malnutrition in the second year of life may have a larger negative impact than malnutrition in the first year of life.
. However, it has been suggested that in IUGR the brain
may be selectively spared. Brain growth is usually less affected than whole body weight or length. Several studies from developed nations have found that with the exception of extreme intrauterine growth retardation also affecting brain growth, and hypoxic
injury, IUGR seems to have little or no measurable effect on mental performance and behavior in adolescence
or adulthood. For example, acute undernutrition for a few months during the Dutch famine of 1944
caused a decrease in mean birthweight in certain areas. This was later associated with a change in performance on IQ tests for 18–19 years old Dutch males draftees from these areas compared to control areas. The subjects were exposed to famine prenatally but not after birth. During the famine
, births decreased more among those with lower Socioeconomic status
(SES), whereas after the famine, there was a compensatory increase in births among those with lower SES. Since SES correlates with IQ, this may have hidden an effect caused by the undernutrition.
Recently, however, the longstanding belief that breastfeeding
causes an increase in the IQ of offspring was challenged in a 2006 paper published in the British Medical Journal
. The results indicated that mother's IQ, not breastfeeding, explained the differences in the IQ scores of offspring measured between ages 5 and 14. The results of this study argued that prior studies had not controlled for the mother's IQ. Since mother's IQ was predictive of whether a child was breastfed, the study concluded that "breast feeding [itself] has little or no effect on intelligence in children." Instead, it was the mother's IQ that had a significant correlation with the IQ of her offspring, whether the offspring was breastfed or was not breastfed. Another study found that breastfeeding had a positive effect on cognitive development at 24 months of age even after controlling for parental IQ.
A potential resolution to these different interpretations was proposed in a study showing that breastfeeding was linked to raised IQ (as much as 7 points when not controlling for maternal IQ) if the infants had an SNP coding for a "C" rather than G base within the FADS2
gene. Those with the "G" version showed no IQ advantage, suggesting a biochemical interaction of child's genes on the effect of breast feeding. Other studies have failed to replicate any correlation between the FADS2 gene, breastfeeding and IQ, while others show a negative effect on IQ when combining bottledfeeding, and the "G" version of FADS2 .
on 18-year-old high-school graduates found that nutritional status during the first year of life affected IQ, scholastic achievement, and brain volume.
deficiencies (e.g. in iodine
and iron) influence the development of intelligence and remain a problem in the developing world. For example, iodine deficiency
causes a fall, in average, of 12 IQ points.
Policy recommendations to increase availability of micronutrient supplements have been made and justified in part by the potential to counteract intelligence-related developmental problems. For example, the Copenhagen consensus
, states that lack of both iodine and iron has been implicated in impaired brain development, and this can affect enormous numbers of people: it is estimated that 2 billion people (one-third of the total global population) are affected by iodine deficiency, including 285 million 6- to 12-year-old children. In developing countries, it is estimated that 40% of children aged four and under suffer from anaemia because of insufficient iron in their diets.
A joint statement on vitamin
and mineral deficiencies says that the severity of such deficiencies "means the impairment of hundreds of millions of growing minds and the lowering of national IQs."
Overall, studies investigating whether cognitive function in already iron-deficient children can be improved with iron supplements have produced mixed results, possibly because deficiency in critical growth periods may cause irreversible damage. However, several studies with better design have shown substantial benefits. One way to prevent iron deficiency is to give specific supplementation to children, for example as tablets. However, this is costly, distribution mechanisms are often ineffective, and compliance
is low. Fortification of staple foods (cereals, flour
, sugar
, salt
) to deliver micronutrients to children on a large scale is probably the most sustainable and affordable option, even though commitment from governments and the food industry is needed. Developed nations fortify several foods with various micronutrients.
Additional vitamin-mineral supplementation may have an effect also in the developed world. A study giving such supplementation to "working class," primarily Hispanic
, 6–12-year-old children in the United States
for 3 months found an average increase of 2 to 3 IQ points. Most of this can be explained by the very large increase of a subgroup of the children, presumably because these were not adequately nourished unlike the majority. The study suggests that parents of schoolchildren whose academic performance is substandard would be well advised to seek a nutritionally oriented physician
for assessment of their children's nutritional status as a possible etiology
.
More speculatively, other nutrients may prove important in the future. Fish oil supplement to pregnant and lactating mothers has been linked to increased cognitive ability in one study. Vitamin B12
and folate may be important for cognitive function in old age.
Another study found that pregnant women who consumed 340 grams of low-mercury containing fish
with fatty acids per week have benefits that outweigh the risks for mercury poisoning
. They were less likely to have children with low verbal IQ, motor coordination
and behavioral problems. However, foods containing high amounts of mercury
, such as shark
, swordfish
, king mackerel
and tilefish
, might cause mental retardation
.
, found that poor growth during infancy, rather than low birth weight, was negatively related to adolescent performance on cognitive and achievement tests. A later related very long term study looked at the effect of giving 6–24-month-old children in Guatemala a high protein-energy drink as a dietary supplement. A significantly positive and fairly substantial effects was found on increasing the probability of attending school and of passing the first grade, increasing the grade attained by age 13, increasing completed schooling attainment, and for adults aged 25–40 increasing IQ test scores.
found that when aged 17–18 years they had significantly poorer scores than a non-stunted group on cognitive and educational tests and psychosocial functioning. Giving a nutritional supplementation (1 kg milk based formula each week) to these already stunted children had no significant effect on later scores, but psychosocial stimulation (weekly play sessions with mother and child) had a positive effect.
, arsenic
, toluene
, and PCB
are well-known causes of neuro-developmental disorders. Recognition of these risks has led to evidence-based programmes of prevention, such as elimination of lead additives in petrol. Although these prevention campaigns are highly successful, most were initiated only after substantial delays.
Policies to manage lead differ between nations, particularly between the developed and developing world. Use of leaded gasoline
has been reduced or eliminated in most developed nations, and lead levels in US children have been substantially reduced by policies relating to lead reduction. Even slightly elevated lead levels around the age of 24 months are associated with intellectual and academic performance deficits at age 10 years.
Certain, at least previously, widely used organochloride
s, such as dioxins, DDT, and PCB
, have been associated with cognitive deficits.
A Lancet review identified 201 chemicals with the ability to cause clinical neurotoxic effects in human adults, as described in the peer-reviewed scientific literature. Most of them are commonly used. Many additional chemicals have been shown to be neurotoxic in laboratory models. The article notes that children are more vulnerable and argues that new, precautionary approaches that recognise the unique vulnerability of the developing brain are needed for testing and control of chemicals in order to avoid the previous substantial before starting restrictions on usage. An appendix listed further industrial chemicals considered to be neurotoxic.
use was found to be significantly correlated in a dose-dependent manner with a decline in IQ scores, during the effect of the use. However, no such decline was seen in subjects who had formerly been heavy cannabis users and had stopped taking the drug. The authors concluded that cannabis does not have a long-term effect on intelligence. Effects on fetal development are minimal when compared with the well-documented adverse effects of tobacco
or alcohol
use.
Fetal alcohol
exposure, causing Fetal alcohol syndrome
, is one of the leading known causes of mental retardation in the Western world.
Maternal tobacco
smoking during pregnancy
is associated with increased activity, decreased attention, and diminished intellectual abilities. However, a recent study finds that maternal tobacco smoking has no direct causal effect on the child's IQ. Adjusting for maternal cognitive ability as measured by IQ and education
eliminated the association between lower IQ and tobacco smoking. But another study instead looking at the relationship between environmental tobacco smoke exposure, measured with a blood biomarker, and cognitive abilities among U.S. children and adolescents 6–16 years of age, found an inverse association between exposure and cognitive deficits among children even at extremely low levels of exposure. The study controlled for sex
, race, region
, poverty
, parent education
and marital status, ferritin
, and blood lead concentration.
, parasites, and cerebral malaria, prenatal drug and alcohol exposure, newborn asphyxia
, low birth weight, head injuries, and endocrine disorders. A direct policy focus on determinants of childhood cognitive ability has been urged.
, and standardized tests, including IQ tests. The study reported that exposure to violence
and trauma-related distress
in young children were associated with substantial decrements in IQ and reading achievement. Exposure to Violence or Trauma lead to a 7.5-point (SD, 0.5) decrement in IQ and a 9.8-point (SD, 0.66) decrement in reading achievement.
Violence may have a negative impact on IQ, or IQ may be protective against violence. The causal mechanism and direction of causation is unknown. Neighborhood risk has been related to lower school grades for African-American adolescents in another study from 2006. Violence may also be more prevalent in the homes of parents with lower IQ's. These parents could have genetically produced children with lower IQ's.
, the rise in intelligence noted in rich countries. Scientific American noted that the study did not show that parasite load
caused low IQ, and Geraint Rees
pointed out that a third factor linked to both IQ scores and infectious disease prevalence could explain the correlation.
affects 300–500 million persons each year, mostly children under age five in Africa
, causing widespread anemia
during a period of rapid brain development and also direct brain damage from cerebral malaria to which children are more vulnerable. A 2006 systematic review found that Plasmodium falciparum
infection causes cognitive deficits in both the short- and long-term. Policies aimed at malaria reduction may have cognitive benefits. It has been suggested that the future economic and educational development of Africa critically depends on the eradication of malaria.
Roundworms infect hundreds of millions of people. There is evidence that high intensities of worms in the intestines can affect mental performance, but a systematic review in 2000 and a 2009 update found that there was insufficient evidence to show that deworming treatments improve cognitive performance or school performance in children.
HIV
infection in children in sub-Saharan Africa affects their motor development, but there is insufficient evidence to show a slowing of language development.
which can cause cognitive impairment. Many of these are associated with aging. Some common examples include Alzheimer's disease
and Multi-infarct dementia
. Many diseases may be neurological or psychiatric and may primarily affect the brain. Others may affect many other organs, like HIV
, Hashimoto's thyroiditis
causing hypothyroidism
, or cancer
.
Major depression, affecting about 16% of the population on at least one occasion in their lives and the leading cause of disability in North America, may give symptoms similar to dementia. Patients treated for depression score higher on IQ tests than before treatment.
and higher IQ and between myopia and school achievement. Several, but not all, studies have found hyperopia
to be associated with lower IQ and school achievements. A common explanation for myopia is near-work. Regarding the relationship to IQ, several explanations have been proposed. One is that the myopic child is better adapted at reading, and reads and studies more, which increases intelligence. The reverse explanation is that the intelligent and studious child reads more which causes myopia. Another is that the myopic child have an advantage at IQ testing which is near work because of less eye strain. Still another explanation is that pleiotropic gene(s) affect the size of both brain and eyes simultaneously. A study of Chinese schoolchildren found that after controlling for age, gender, school, parental myopia, father’s education, and books read per week, myopia was still associated with high nonverbal IQ. Nonverbal IQ was a more important explanation than books read per week.
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...
can affect intelligence
Intelligence
Intelligence has been defined in different ways, including the abilities for abstract thought, understanding, communication, reasoning, learning, planning, emotional intelligence and problem solving....
in various ways. This is one of the most important factors in understanding the origins of human group differences in IQ test scores and other measures of cognitive ability. Several factors can lead to significant cognitive impairment, particularly if they occur during pregnancy and childhood when the brain is growing and the blood-brain barrier
Blood-brain barrier
The blood–brain barrier is a separation of circulating blood and the brain extracellular fluid in the central nervous system . It occurs along all capillaries and consists of tight junctions around the capillaries that do not exist in normal circulation. Endothelial cells restrict the diffusion...
is less effective. Such impairment may sometimes be permanent, sometimes be partially or wholly compensated for by later growth.
Developed nations have implemented several health policies regarding nutrients and toxins known to influence cognitive function. These include laws requiring fortification
Food fortification
Food fortification or enrichment is the process of adding micronutrients to food. It can be purely a commercial choice to provide extra nutrients in a food, or sometimes it is a public health policy which aims to reduce numbers of people with dietary deficiencies in a population.Diets that lack...
of certain food products and laws establishing safe levels of pollutants (e.g. lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
, mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
, and organochloride
Organochloride
An organochloride, organochlorine, chlorocarbon, chlorinated hydrocarbon, or chlorinated solvent is an organic compound containing at least one covalently bonded chlorine atom. Their wide structural variety and divergent chemical properties lead to a broad range of applications...
s). Comprehensive policy recommendations targeting reduction of cognitive impairment in children have been proposed.
Improvements in nutrition
Nutrition
Nutrition is the provision, to cells and organisms, of the materials necessary to support life. Many common health problems can be prevented or alleviated with a healthy diet....
, and in public policy in general, have been implicated in worldwide IQ increases (the Flynn effect
Flynn effect
The Flynn effect is the name given to a substantial and long-sustained increase in intelligence test scores measured in many parts of the world. When intelligence quotient tests are initially standardized using a sample of test-takers, by convention the average of the test results is set to 100...
) .
Nutrition
Malnutrition may occur during several periods of growth, such as pregnancyPregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
, during breastfeeding
Breastfeeding
Breastfeeding is the feeding of an infant or young child with breast milk directly from female human breasts rather than from a baby bottle or other container. Babies have a sucking reflex that enables them to suck and swallow milk. It is recommended that mothers breastfeed for six months or...
, infancy, or childhood. It may also happen due to deficiencies of different nutrients, such as micronutrients, protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
or energy. This may cause different effects.
Timing
Some observers have argued that malnutritionMalnutrition
Malnutrition is the condition that results from taking an unbalanced diet in which certain nutrients are lacking, in excess , or in the wrong proportions....
during the first six months of life harms cognitive development much more than malnutrition later in life. However, a study from the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
argues that malnutrition in the second year of life may have a larger negative impact than malnutrition in the first year of life.
Intrauterine growth retardation
Undernutrition during pregnancy, and other factors, may cause intrauterine growth retardation (IUGR), which is one cause of low birth weightLow birth weight
Low birth weight is defined as a birth weight of a liveborn infant of less than 2,500 g. regardless of gestational age-Causes:LBW is either the result of preterm birth or of the infant being small for gestational age , or a combination of...
. However, it has been suggested that in IUGR the brain
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,...
may be selectively spared. Brain growth is usually less affected than whole body weight or length. Several studies from developed nations have found that with the exception of extreme intrauterine growth retardation also affecting brain growth, and hypoxic
Hypoxia (medical)
Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
injury, IUGR seems to have little or no measurable effect on mental performance and behavior in adolescence
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...
or adulthood. For example, acute undernutrition for a few months during the Dutch famine of 1944
Dutch famine of 1944
The Dutch famine of 1944, known as the Hongerwinter in Dutch, was a famine that took place in the German-occupied part of the Netherlands, especially in the densely populated western provinces above the great rivers, during the winter of 1944-1945, near the end of World War II. A German blockade...
caused a decrease in mean birthweight in certain areas. This was later associated with a change in performance on IQ tests for 18–19 years old Dutch males draftees from these areas compared to control areas. The subjects were exposed to famine prenatally but not after birth. During the famine
Famine
A famine is a widespread scarcity of food, caused by several factors including crop failure, overpopulation, or government policies. This phenomenon is usually accompanied or followed by regional malnutrition, starvation, epidemic, and increased mortality. Every continent in the world has...
, births decreased more among those with lower 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...
(SES), whereas after the famine, there was a compensatory increase in births among those with lower SES. Since SES correlates with IQ, this may have hidden an effect caused by the undernutrition.
Breastfeeding
Studies often find higher IQ in children and adults who were breastfed. It has also been proposed that the omega-3 fatty acids that are found in high doses in breast milk, and that are known to be essential constituents of brain tissues, could at least partially account for an increase in IQ.Recently, however, the longstanding belief that breastfeeding
Breastfeeding
Breastfeeding is the feeding of an infant or young child with breast milk directly from female human breasts rather than from a baby bottle or other container. Babies have a sucking reflex that enables them to suck and swallow milk. It is recommended that mothers breastfeed for six months or...
causes an increase in the IQ of offspring was challenged in a 2006 paper published in the British Medical Journal
British Medical Journal
BMJ is a partially open-access peer-reviewed medical journal. Originally called the British Medical Journal, the title was officially shortened to BMJ in 1988. The journal is published by the BMJ Group, a wholly owned subsidiary of the British Medical Association...
. The results indicated that mother's IQ, not breastfeeding, explained the differences in the IQ scores of offspring measured between ages 5 and 14. The results of this study argued that prior studies had not controlled for the mother's IQ. Since mother's IQ was predictive of whether a child was breastfed, the study concluded that "breast feeding [itself] has little or no effect on intelligence in children." Instead, it was the mother's IQ that had a significant correlation with the IQ of her offspring, whether the offspring was breastfed or was not breastfed. Another study found that breastfeeding had a positive effect on cognitive development at 24 months of age even after controlling for parental IQ.
A potential resolution to these different interpretations was proposed in a study showing that breastfeeding was linked to raised IQ (as much as 7 points when not controlling for maternal IQ) if the infants had an SNP coding for a "C" rather than G base within the FADS2
FADS2
Fatty acid desaturase 2 also known as delta fatty acid desaturase is an enzyme that in humans is encoded by the FADS2 gene.- Function :Fatty acid desaturase 2 is a member of the fatty acid desaturase gene family...
gene. Those with the "G" version showed no IQ advantage, suggesting a biochemical interaction of child's genes on the effect of breast feeding. Other studies have failed to replicate any correlation between the FADS2 gene, breastfeeding and IQ, while others show a negative effect on IQ when combining bottledfeeding, and the "G" version of FADS2 .
Infancy
Two studies in ChileChile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
on 18-year-old high-school graduates found that nutritional status during the first year of life affected IQ, scholastic achievement, and brain volume.
Micronutrients and vitamin deficiencies
MicronutrientMicronutrient
Micronutrients are nutrients required by humans and other living things throughout life in small quantities to orchestrate a whole range of physiological functions, but which the organism itself cannot produce. For people, they include dietary trace minerals in amounts generally less than 100...
deficiencies (e.g. in iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
and iron) influence the development of intelligence and remain a problem in the developing world. For example, iodine deficiency
Iodine deficiency
Iodine is an essential trace element; the thyroid hormones thyroxine and triiodotyronine contain iodine. In areas where there is little iodine in the diet—typically remote inlandareas where no marine foods are eaten—iodine deficiency gives rise to...
causes a fall, in average, of 12 IQ points.
Policy recommendations to increase availability of micronutrient supplements have been made and justified in part by the potential to counteract intelligence-related developmental problems. For example, the Copenhagen consensus
Copenhagen Consensus
Copenhagen Consensus is a project that seeks to establish priorities for advancing global welfare using methodologies based on the theory of welfare economics. It was conceived and organized by Bjørn Lomborg, the author of The Skeptical Environmentalist and the then director of the Danish...
, states that lack of both iodine and iron has been implicated in impaired brain development, and this can affect enormous numbers of people: it is estimated that 2 billion people (one-third of the total global population) are affected by iodine deficiency, including 285 million 6- to 12-year-old children. In developing countries, it is estimated that 40% of children aged four and under suffer from anaemia because of insufficient iron in their diets.
A joint statement on vitamin
Vitamin
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...
and mineral deficiencies says that the severity of such deficiencies "means the impairment of hundreds of millions of growing minds and the lowering of national IQs."
Overall, studies investigating whether cognitive function in already iron-deficient children can be improved with iron supplements have produced mixed results, possibly because deficiency in critical growth periods may cause irreversible damage. However, several studies with better design have shown substantial benefits. One way to prevent iron deficiency is to give specific supplementation to children, for example as tablets. However, this is costly, distribution mechanisms are often ineffective, and compliance
Compliance (regulation)
In general, compliance means conforming to a rule, such as a specification, policy, standard or law. Regulatory compliance describes the goal that corporations or public agencies aspire to in their efforts to ensure that personnel are aware of and take steps to comply with relevant laws and...
is low. Fortification of staple foods (cereals, flour
Flour
Flour is a powder which is made by grinding cereal grains, other seeds or roots . It is the main ingredient of bread, which is a staple food for many cultures, making the availability of adequate supplies of flour a major economic and political issue at various times throughout history...
, sugar
Sugar
Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...
, salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
) to deliver micronutrients to children on a large scale is probably the most sustainable and affordable option, even though commitment from governments and the food industry is needed. Developed nations fortify several foods with various micronutrients.
Additional vitamin-mineral supplementation may have an effect also in the developed world. A study giving such supplementation to "working class," primarily Hispanic
Hispanic
Hispanic is a term that originally denoted a relationship to Hispania, which is to say the Iberian Peninsula: Andorra, Gibraltar, Portugal and Spain. During the Modern Era, Hispanic sometimes takes on a more limited meaning, particularly in the United States, where the term means a person of ...
, 6–12-year-old children in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
for 3 months found an average increase of 2 to 3 IQ points. Most of this can be explained by the very large increase of a subgroup of the children, presumably because these were not adequately nourished unlike the majority. The study suggests that parents of schoolchildren whose academic performance is substandard would be well advised to seek a nutritionally oriented physician
Physician
A physician is a health care provider who practices the profession of medicine, which is concerned with promoting, maintaining or restoring human health through the study, diagnosis, and treatment of disease, injury and other physical and mental impairments...
for assessment of their children's nutritional status as a possible etiology
Etiology
Etiology is the study of causation, or origination. The word is derived from the Greek , aitiologia, "giving a reason for" ....
.
More speculatively, other nutrients may prove important in the future. Fish oil supplement to pregnant and lactating mothers has been linked to increased cognitive ability in one study. Vitamin B12
Vitamin B12
Vitamin B12, vitamin B12 or vitamin B-12, also called cobalamin, is a water-soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins...
and folate may be important for cognitive function in old age.
Another study found that pregnant women who consumed 340 grams of low-mercury containing fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
with fatty acids per week have benefits that outweigh the risks for mercury poisoning
Mercury poisoning
Mercury poisoning is a disease caused by exposure to mercury or its compounds. Mercury is a heavy metal occurring in several forms, all of which can produce toxic effects in high enough doses...
. They were less likely to have children with low verbal IQ, motor coordination
Motor coordination
thumb|right|Motor coordination is shown in this animated sequence by [[Eadweard Muybridge]] of himself throwing a diskMotor coordination is the combination of body movements created with the kinematic and kinetic parameters that result in intended actions. Such movements usually smoothly and...
and behavioral problems. However, foods containing high amounts of mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
, such as shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
, swordfish
Swordfish
Swordfish , also known as broadbill in some countries, are large, highly migratory, predatory fish characterized by a long, flat bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood...
, king mackerel
King mackerel
The king mackerel is a migratory species of mackerel of the western Atlantic Ocean and Gulf of Mexico. It is an important species to both the commercial and recreational fishing industries.-Description:...
and tilefish
Tilefish
Tilefishes, also known as blanquillo, are mostly small perciform marine fish comprising the family Malacanthidae.They are usually found in sandy areas, especially near coral reefs....
, might cause mental retardation
Mental retardation
Mental retardation is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors...
.
Protein and energy malnutrition
One study from a developing country, GuatemalaGuatemala
Guatemala is a country in Central America bordered by Mexico to the north and west, the Pacific Ocean to the southwest, Belize to the northeast, the Caribbean to the east, and Honduras and El Salvador to the southeast...
, found that poor growth during infancy, rather than low birth weight, was negatively related to adolescent performance on cognitive and achievement tests. A later related very long term study looked at the effect of giving 6–24-month-old children in Guatemala a high protein-energy drink as a dietary supplement. A significantly positive and fairly substantial effects was found on increasing the probability of attending school and of passing the first grade, increasing the grade attained by age 13, increasing completed schooling attainment, and for adults aged 25–40 increasing IQ test scores.
Stunting
31% of children under the age of 5 in the developing world are moderately (height-for-age is below minus 2 standard deviations) or severely stunted (below minus 3 standard deviations). The prevalence was even higher previously since the worldwide prevalence of stunting is declining by about half of a percentage point each year. A study on stunted children aged 9–24 months in JamaicaJamaica
Jamaica is an island nation of the Greater Antilles, in length, up to in width and 10,990 square kilometres in area. It is situated in the Caribbean Sea, about south of Cuba, and west of Hispaniola, the island harbouring the nation-states Haiti and the Dominican Republic...
found that when aged 17–18 years they had significantly poorer scores than a non-stunted group on cognitive and educational tests and psychosocial functioning. Giving a nutritional supplementation (1 kg milk based formula each week) to these already stunted children had no significant effect on later scores, but psychosocial stimulation (weekly play sessions with mother and child) had a positive effect.
Industrial chemicals
Certain toxins, such as lead, mercuryMercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
, arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
, toluene
Toluene
Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. It is a mono-substituted benzene derivative, i.e., one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3.It is an aromatic...
, and PCB
Polychlorinated biphenyl
Polychlorinated biphenyls are a class of organic compounds with 2 to 10 chlorine atoms attached to biphenyl, which is a molecule composed of two benzene rings. The chemical formula for PCBs is C12H10-xClx...
are well-known causes of neuro-developmental disorders. Recognition of these risks has led to evidence-based programmes of prevention, such as elimination of lead additives in petrol. Although these prevention campaigns are highly successful, most were initiated only after substantial delays.
Policies to manage lead differ between nations, particularly between the developed and developing world. Use of leaded gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...
has been reduced or eliminated in most developed nations, and lead levels in US children have been substantially reduced by policies relating to lead reduction. Even slightly elevated lead levels around the age of 24 months are associated with intellectual and academic performance deficits at age 10 years.
Certain, at least previously, widely used organochloride
Organochloride
An organochloride, organochlorine, chlorocarbon, chlorinated hydrocarbon, or chlorinated solvent is an organic compound containing at least one covalently bonded chlorine atom. Their wide structural variety and divergent chemical properties lead to a broad range of applications...
s, such as dioxins, DDT, and PCB
Polychlorinated biphenyl
Polychlorinated biphenyls are a class of organic compounds with 2 to 10 chlorine atoms attached to biphenyl, which is a molecule composed of two benzene rings. The chemical formula for PCBs is C12H10-xClx...
, have been associated with cognitive deficits.
A Lancet review identified 201 chemicals with the ability to cause clinical neurotoxic effects in human adults, as described in the peer-reviewed scientific literature. Most of them are commonly used. Many additional chemicals have been shown to be neurotoxic in laboratory models. The article notes that children are more vulnerable and argues that new, precautionary approaches that recognise the unique vulnerability of the developing brain are needed for testing and control of chemicals in order to avoid the previous substantial before starting restrictions on usage. An appendix listed further industrial chemicals considered to be neurotoxic.
Recreational drugs
Current cannabisCannabis
Cannabis is a genus of flowering plants that includes three putative species, Cannabis sativa, Cannabis indica, and Cannabis ruderalis. These three taxa are indigenous to Central Asia, and South Asia. Cannabis has long been used for fibre , for seed and seed oils, for medicinal purposes, and as a...
use was found to be significantly correlated in a dose-dependent manner with a decline in IQ scores, during the effect of the use. However, no such decline was seen in subjects who had formerly been heavy cannabis users and had stopped taking the drug. The authors concluded that cannabis does not have a long-term effect on intelligence. Effects on fetal development are minimal when compared with the well-documented adverse effects of tobacco
Tobacco
Tobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as a pesticide and, in the form of nicotine tartrate, used in some medicines...
or alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
use.
Fetal alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
exposure, causing Fetal alcohol syndrome
Fetal alcohol syndrome
Fetal alcohol syndrome is a pattern of mental and physical defects that can develop in a fetus in association with high levels of alcohol consumption during pregnancy. Current research also implicates other lifestyle choices made by the prospective mother...
, is one of the leading known causes of mental retardation in the Western world.
Maternal tobacco
Tobacco
Tobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as a pesticide and, in the form of nicotine tartrate, used in some medicines...
smoking during pregnancy
Smoking and pregnancy
Tobacco smoking and pregnancy is related to many effects on health and reproduction, in addition to the general health effects of tobacco. A number of studies have shown that tobacco use is a significant factor in miscarriages among pregnant smokers, and that it contributes to a number of other...
is associated with increased activity, decreased attention, and diminished intellectual abilities. However, a recent study finds that maternal tobacco smoking has no direct causal effect on the child's IQ. Adjusting for maternal cognitive ability as measured by IQ and education
Education
Education in its broadest, general sense is the means through which the aims and habits of a group of people lives on from one generation to the next. Generally, it occurs through any experience that has a formative effect on the way one thinks, feels, or acts...
eliminated the association between lower IQ and tobacco smoking. But another study instead looking at the relationship between environmental tobacco smoke exposure, measured with a blood biomarker, and cognitive abilities among U.S. children and adolescents 6–16 years of age, found an inverse association between exposure and cognitive deficits among children even at extremely low levels of exposure. The study controlled for sex
Sex
In biology, sex is a process of combining and mixing genetic traits, often resulting in the specialization of organisms into a male or female variety . Sexual reproduction involves combining specialized cells to form offspring that inherit traits from both parents...
, race, region
Region
Region is most commonly found as a term used in terrestrial and astrophysics sciences also an area, notably among the different sub-disciplines of geography, studied by regional geographers. Regions consist of subregions that contain clusters of like areas that are distinctive by their uniformity...
, poverty
Poverty
Poverty is the lack of a certain amount of material possessions or money. Absolute poverty or destitution is inability to afford basic human needs, which commonly includes clean and fresh water, nutrition, health care, education, clothing and shelter. About 1.7 billion people are estimated to live...
, parent education
Education
Education in its broadest, general sense is the means through which the aims and habits of a group of people lives on from one generation to the next. Generally, it occurs through any experience that has a formative effect on the way one thinks, feels, or acts...
and marital status, ferritin
Ferritin
Ferritin is a ubiquitous intracellular protein that stores iron and releases it in a controlled fashion. The amount of ferritin stored reflects the amount of iron stored. The protein is produced by almost all living organisms, including bacteria, algae and higher plants, and animals...
, and blood lead concentration.
Healthcare during pregnancy and childbirth
Healthcare during pregnancy and childbirth, access to which is often governed by policy, also influences cognitive development. Preventable causes of low intelligence in children include infectious diseases such as meningitisMeningitis
Meningitis is inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. The inflammation may be caused by infection with viruses, bacteria, or other microorganisms, and less commonly by certain drugs...
, parasites, and cerebral malaria, prenatal drug and alcohol exposure, newborn asphyxia
Asphyxia
Asphyxia or asphyxiation is a condition of severely deficient supply of oxygen to the body that arises from being unable to breathe normally. An example of asphyxia is choking. Asphyxia causes generalized hypoxia, which primarily affects the tissues and organs...
, low birth weight, head injuries, and endocrine disorders. A direct policy focus on determinants of childhood cognitive ability has been urged.
Stress
A recent theory suggests that early childhood stress may affect the developing brain and cause negative effects. Exposure to violence in childhood has been associated with lower school grades and lower IQ in children of all races. A group of largely African American urban first-grade children and their caregivers were evaluated using self-report, interviewInterview
An interview is a conversation between two people where questions are asked by the interviewer to obtain information from the interviewee.- Interview as a Method for Qualitative Research:"Definition" -...
, and standardized tests, including IQ tests. The study reported that exposure to violence
Violence
Violence is the use of physical force to apply a state to others contrary to their wishes. violence, while often a stand-alone issue, is often the culmination of other kinds of conflict, e.g...
and trauma-related distress
Psychological trauma
Psychological trauma is a type of damage to the psyche that occurs as a result of a traumatic event...
in young children were associated with substantial decrements in IQ and reading achievement. Exposure to Violence or Trauma lead to a 7.5-point (SD, 0.5) decrement in IQ and a 9.8-point (SD, 0.66) decrement in reading achievement.
Violence may have a negative impact on IQ, or IQ may be protective against violence. The causal mechanism and direction of causation is unknown. Neighborhood risk has been related to lower school grades for African-American adolescents in another study from 2006. Violence may also be more prevalent in the homes of parents with lower IQ's. These parents could have genetically produced children with lower IQ's.
Infectious diseases
A 2010 study by Eppig, Fincher and Thornhill found a close correlation between the infectious disease burden in a country and the average IQ of its population. The researchers found that when disease was controlled for, IQ showed no correlation with other variables such as educational and nutritional levels. Since brain development requires a very high proportion of all the body's energy in newborns and children, the researchers argue that fighting infection reduces children's IQ potential. The Eppig research may help to explain the Flynn effectFlynn effect
The Flynn effect is the name given to a substantial and long-sustained increase in intelligence test scores measured in many parts of the world. When intelligence quotient tests are initially standardized using a sample of test-takers, by convention the average of the test results is set to 100...
, the rise in intelligence noted in rich countries. Scientific American noted that the study did not show that parasite load
Parasite load
Parasite load is a measure of the number and virulence of the parasites that a host organism harbours. Quantitative parasitology deals with measures to quantify parasite loads in samples of hosts and to make statistical comparisons of parasitism across host samples.In evolutionary biology, parasite...
caused low IQ, and Geraint Rees
Geraint Rees
Geraint Rees FMedSci is Director of the UCL Institute of Cognitive Neuroscience and a Professor of Cognitive Neurology and Wellcome Trust Senior Clinical Fellow at University College London.-Biography:...
pointed out that a third factor linked to both IQ scores and infectious disease prevalence could explain the correlation.
Tropical infectious diseases
MalariaMalaria
Malaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. The disease results from the multiplication of Plasmodium parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases...
affects 300–500 million persons each year, mostly children under age five in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, causing widespread anemia
Anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
during a period of rapid brain development and also direct brain damage from cerebral malaria to which children are more vulnerable. A 2006 systematic review found that Plasmodium falciparum
Plasmodium falciparum
Plasmodium falciparum is a protozoan parasite, one of the species of Plasmodium that cause malaria in humans. It is transmitted by the female Anopheles mosquito. Malaria caused by this species is the most dangerous form of malaria, with the highest rates of complications and mortality...
infection causes cognitive deficits in both the short- and long-term. Policies aimed at malaria reduction may have cognitive benefits. It has been suggested that the future economic and educational development of Africa critically depends on the eradication of malaria.
Roundworms infect hundreds of millions of people. There is evidence that high intensities of worms in the intestines can affect mental performance, but a systematic review in 2000 and a 2009 update found that there was insufficient evidence to show that deworming treatments improve cognitive performance or school performance in children.
HIV
HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
infection in children in sub-Saharan Africa affects their motor development, but there is insufficient evidence to show a slowing of language development.
Effects of other diseases
There are numerous diseases affecting the central nervous systemCentral nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
which can cause cognitive impairment. Many of these are associated with aging. Some common examples include Alzheimer's disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...
and Multi-infarct dementia
Multi-infarct dementia
Multi-infarct dementia is one type of vascular dementia. Vascular dementia is the second most common form of dementia after Alzheimer's disease in older adults. Multi-infarct dementia is thought to be an irreversible form of dementia, and its onset is caused by a number of small strokes or...
. Many diseases may be neurological or psychiatric and may primarily affect the brain. Others may affect many other organs, like HIV
HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
, 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...
causing hypothyroidism
Hypothyroidism
Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or...
, or cancer
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...
.
Major depression, affecting about 16% of the population on at least one occasion in their lives and the leading cause of disability in North America, may give symptoms similar to dementia. Patients treated for depression score higher on IQ tests than before treatment.
Myopia and hyperopia
A 2008 literature review writes that studies in several nations have found a relationship between myopiaMyopia
Myopia , "shortsightedness" ) is a refractive defect of the eye in which collimated light produces image focus in front of the retina under conditions of accommodation. In simpler terms, myopia is a condition of the eye where the light that comes in does not directly focus on the retina but in...
and higher IQ and between myopia and school achievement. Several, but not all, studies have found hyperopia
Hyperopia
Hyperopia, also known as farsightedness, longsightedness or hypermetropia, is a defect of vision caused by an imperfection in the eye , causing difficulty focusing on near objects, and in extreme cases causing a sufferer to be unable to focus on objects at any distance...
to be associated with lower IQ and school achievements. A common explanation for myopia is near-work. Regarding the relationship to IQ, several explanations have been proposed. One is that the myopic child is better adapted at reading, and reads and studies more, which increases intelligence. The reverse explanation is that the intelligent and studious child reads more which causes myopia. Another is that the myopic child have an advantage at IQ testing which is near work because of less eye strain. Still another explanation is that pleiotropic gene(s) affect the size of both brain and eyes simultaneously. A study of Chinese schoolchildren found that after controlling for age, gender, school, parental myopia, father’s education, and books read per week, myopia was still associated with high nonverbal IQ. Nonverbal IQ was a more important explanation than books read per week.