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Nutrition, Health, Toxins

Nutrition​

Since the human brain attains 60% of its adult weight in the first year after birth and more than triples its weight in the first 24 months, it should not be surprising that prenatal and infant nutrition can have significant effects on brain development1. Severe undernutrition before two or three years of age, especially a lack of proteins and vitamins and minerals essential for their anabolism, results in lowered intelligence. It is crucial to note that a diet may have adequate caloric intake and still be deficient in protein, iron, or further substances important for neural development. However, ultimately, malnutrition to a level that would influence neural development, and hence intelligence, is rare in developed countries.

Stoch and Smythe (1963)2 found that extremely malnourished South African colored children were some 20 points lower in IQ than children of similar parents who had not suffered from malnutrition. The difference between the undernourished group and the control group in DQ (Developmental Quotient) and IQ over the age range from 1 year to 8 years was practically constant. If undernutrition takes a toll, it takes it early, as shown by the lower DQs at 1 year and the absence of any increase in the decrement at the later ages. This study also revealed that the undernourished children had smaller stature and head circumference than the control children. Although there is no correlation between intelligence and head circumference in normally nourished children, there is a positive correlation between these factors in groups whose numbers suffer varying degrees of undernutrition early in life. Undernutrition also increases the correlation between intelligence and physical stature.

Undernutrition occurring for the first time in older children seems to have no permanent effect. Severely malnourished war prisoners, for example, function intellectually at their expected level when they are returned to normal living conditions.

Even as late as 2 years of age, a gain of as much as 18 IQ points was produced by nutritional improvements in a group of extremely undernourished children. After 4 years of age, however, nutritional therapy effected no significant change in IQ3.

Early and Brief Malnutrition​

Brief periods of malnutrition do not appear to leave permanent effects, even when the malnutrition occurs in utero or in infancy. The evidence for this comes from a large, quasi-experimental study4 that occurred during a period of starvation in the northern region of the Netherlands as a by-product of a Nazi blockade during World War II. At one point. the estimated caloric content of rations was down to 640 calories per adult per day. Meanwhile, the southern Dutch cities, under Allied control, received adequate food. The starvation period lasted from September until March, when US troops liberated the northern Dutch cities and supplied food. The war in Europe ended shortly thereafter. In the Netherlands postwar, men register for military service at age nineteen. All registrants complete a progressive matrix test. Zena Stein and her colleagues (1972)[tk] from Columbia University compared the scores of men who were in utero or neonates while living in the northern Dutch cities during the months of the starvation period to the scores of men who had been born at the same time but had lived in the cities under Allied control. Other records of mental ability, such as the frequency of mental disability, were also compared across the two populations. There was no difference in any indicator of mental competence. This study of more than 125,000 men provides striking evidence of the resilience of human cognition. Apparently, any effects of severe short-term malnutrition are not permanent. The key results are shown below. However, chronic, prolonged malnutrition shows different results.

brief malnutrition

Famine, birth weight, and intelligence. (top) Mean birth weight in maternity hospitals selected from famine and control cities by cohort birth. (bottom) Mean scores on Raven’s Progressive Matrices of Netherlands men examined at age nineteen, for manual and nonmanual classes according to father’s occupation, by cohort of birth in famine cities and control cities. Solid vertical lines bracket the period of famine, and dashed vertical lines show the period of births of children conceived during famine (Stein et al., 1972)[tk].

The Malnourished Cognitive Profile​

Malnourished children are described as less attentive, more impulsive, and easily distracted. Researchers primarily interested in nutrition describe this as a confounding variable, saying it is unclear whether the effects of malnutrition are on intelligence or whether they are on attention5. The behaviors that characterize malnourished children are indications of lack of cognitive control, which is a vital part of the working memory system [tk]. From this perspective, malnutrition might directly influence intelligence scores because the act of taking the test requires exercise of the working memory system. The same deficiencies in information processing influence young children's school performance, resulting in a deficiency in the knowledge-based aspects of intelligence. Thus, a physical agent like malnutrition results in an inability to benefit from environmental supports that may contribute to better cognition.

The results of a study conducted in rural Guatemala are particularly informative. Protein supplementation was provided for some children, while a nonprotein supplement was offered to others. Protein supplementation improved various measures of cognitive performance. In addition, there was an important interaction: the greatest gains occurred when protein supplementation was combined with school attendance6. This is consistent with the argument that appropriate nutrition will benefit working memory and related cognitive processes. These effects make it possible to take advantage of an environment that supports the development of cognitive abilities and skills. A policy implication is that, for optimal effect, a supplementation program to help children recover from malnutrition should be combined with an educational program.

Studies in low-income nations have provided evidence that prolonged malnutrition is associated with low cognitive test scores, particularly on nonverbal tests.

Micronutrients & Supplements​

Micronutrients are essential vitamins and minerals needed in small amounts by the body for proper metabolic functioning. Most micronutrients cannot be synthesized in sufficient quantities and therefore must be obtained through the diet. Some important micronutrients include:

  • Vitamins - B12, D, folate
  • Minerals - iron, iodine, zinc
  • Fatty Acids - DHA and EPA
  • Amino Acids - tryptophan, phenylalanine, lysine

Deficiencies in the consumption of micronutrients are a major contributor to poor health in developing countries. For example, in 2005, some 667,000 deaths of children under five (6.3% of all such deaths worldwide) were estimated to be attributable to vitamin A deficiency. The mortality burden of zinc deficiency was roughly two-thirds as large. Anemia, the most important cause of which is inadequate intake of iron, affects 1.6 billion people around the globe7.

Iodine​

World Health Organization estimates that nearly 50 million people suffer some degree of mental impairment due to iodine deficiency, and that this is the leading cause of preventable mental retardation in the world7. Eliminating iodine deficiency around the globe is an ongoing project, largely through the introduction of iodized salt. In the US iodine deficiency was a significant problem in the early part of the 20th century with rates of deficiency similar to those faced by the worst afflicted developing countries today.

Iodine supplementation during pregnancy or infancy can raise average IQs in the worst-off regions by 12 IQ points8; such an increase is of considerable economic value, even in developed countries with iodization programs.

Creatine (Misc)​

Creatine is a naturally occurring compound derived from amino acids. Creatine is synthesized in the liver, kidneys, and pancreas, but also obtained in the diet, especially through red meat and fish. Creatine is considered a conditionally essential nutrient—under certain conditions, endogenous synthesis is inadequate, and dietary creatine becomes essential. These conditions include:

  • Periods of rapid growth (infancy, adolescence)
  • Neurodevelopmental or mitochondrial disorders
  • Vegan or vegetarian diets (low to zero dietary creatine intake)
  • High cognitive or physical demand states

Creatine is used as a supplement by sportsmen to increase athletic performance by improving energy supply to muscle tissues. It is also an important brain compound and some hypothesize that it aids cognition by improving energy supply and neuroprotection. A 2018 meta-analysis9 concluded that oral creatine administration may improve short-term memory and intelligence/reasoning in healthy individuals but its effect on other cognitive domains (long-term memory, attention, executive function, word fluency, etc.) remains unclear. Findings suggest particular benefit for aging, stressed, and sleep-deprived individuals. Vegetarians responded better than meat-eaters in memory tasks but for other cognitive domains no differences were observed.

Toxins and Drugs​

Bruce Lanphear published a perspective article in 2017 with the title "Low-Level Toxicity of Chemicals: No Acceptable Levels?"10. The key message was that societies need to achieve zero exposure to chemicals such as lead, radon, airborne particles, asbestos, and benzene because "the amount of toxic chemical linked with the development of a disease is proportionately greater at the lowest dose or levels of exposure". The next figure [tk] depicts this visually with respect to blood lead levels and IQ scores.

Lead​

Lead is a pollutant that has presented a large problem worldwide and was one of the first metals mined. Analysis of human remains shows that prior to the beginning of metallurgy, about 4000 BCE, the concentration of lead in the human body was 0.0016 micrograms per deciliter (µg/dl). In 1975–1980, the concentration in US children was estimated to be fifteen micrograms per deciliter, more than 1,000 times the natural level. The concentration has fallen markedly since then, due largely to the banning of tetraethyl, lead-added gasoline11.

Lead poisoning, especially during childhood, can have lasting negative effects on personality, leading to individuals being less agreeable, less conscientious, and more neurotic in adulthood. There is substantial evidence linking lead exposure to a heightened risk of criminal behavior, particularly violent crimes. This aligns with earlier research suggesting lead exposure may foster impulsive and aggressive tendencies, potential precursors to violent offenses (see "The lead-crime hypothesis: A meta-analysis")

Today’s concerns are about the cumulative effects of exposures to much lower concentrations of atmospheric lead and, in particular, the effects on children.

Atmospheric Lead and IQ​

In 2005, a consortium of researchers involved in lead-IQ studies published an analysis of the international findings12. They concluded that there is a nonlinear relationship between intelligence test scores and the level of lead in the blood. The decreases are cumulative, so the expected loss for a child with a thirty micrograms per deciliter concentration of lead in the blood was almost half a standard deviation (6.9 IQ points).

The graph below depicts the function relating blood lead levels and IQ scores and the sobering main conclusion of Lanphear's perspective article10: "An increase in blood lead from <1 µ/dL to 30 µ/dL was associated with a 9.2 IQ deficit, but the largest fraction of this deficit (6.2 IQ points) occurred below 10 µ/dL. … Despite the dramatic decline in blood lead levels, lead exposure accounts for a loss of 32 million IQ points in a 6-year birth cohort of US children".

blood lead and iq

Decelerating dose–response curve relating blood lead and IQ score. (Lanphear, 2017)

Both prenatal levels of lead and postnatal increases of lead are associated with decreased intelligence test scores. There is no evidence of threshold effects, [tk] which suggests that the typical recommendation of maintaining a permissible concentration level of ten micrograms per deciliter is inadvisable and dangerous. In a similar vein, the scientific consensus is that no "safe" level of lead in the human bloodstream exists as such; any amount can contribute to neurological problems and other health issues13.

In industrial and postindustrial countries, these findings have an implication on public policy. "Actions to reduce lead concentrations are now recommended by the US Centers for Disease Control and Prevention (CDC), as of 2012, when children’s blood levels exceed five micrograms per deciliter. The 2012 CDC advisory committee report maintained that blood concentrations higher than forty-five micrograms per deciliter require medical treatment (see "Testing for Lead Poisoning in Children").

Alcohol​

Alcohol is the most common and most abused recreational drug in the world. Alcoholism is diagnosed using four criteria:

  1. Craving: A strong compulsion to drink. This goes well beyond thinking it would be nice to have wine with your meal
  2. Loss of control: The inability to cease drinking once drinking has begun
  3. Withdrawal symptoms: Nausea, sweating, shakiness, and anxiety when alcohol use is stopped.
  4. Tolerance: The need to drink ever greater amounts of alcohol to experience symptoms of intoxication, including relaxation and euphoria."

Brain imaging studies of alcohol abusers compared to age-matched controls have suggested that prolonged alcoholism damages the frontal lobes14. This damage is accompanied by decrements in abstract reasoning and in visuospatial reasoning. Both are sorts of behaviors that one associates with decreased working memory, loss of the ability to plan actions, and diminished cognitive control. Extremely heavy, prolonged drinking also can produce damage to the limbic system with an associated loss of the ability to store new memories (Korsakoff’s syndrome). Korsakoff’s syndrome patients are unable to function in society and require hospitalization.

Social Drinking​

The effects of social drinking are less clear. Surveys of social drinkers indicate a small negative association between moderate social drinking and intelligence scores15. Not surprisingly, the effect is strongest among those who consume alcohol more than four times a week and who regularly consume more than forty to fifty milliliters of alcohol per occasion. This is roughly equivalent to three or four drinks of hard liquor, glasses of wine, or bottles of beer.

However, it is difficult to disentangle the effects of social drinking from inherited intellectual potential, health practices, and other lifestyle variables. There is the chicken-and-egg problem: does heavy social drinking reduce intelligence, or is it the case that the intelligent person is less likely to drink heavily on a regular basis? This question is hard to answer because there are data indicating that childhood intelligence scores (measures of cognitive ability taken before people begin to drink) predict drinking patterns. People with higher intelligence scores are less likely to drink to the point of having a hangover and are more likely to consume wine16, which is generally drunk more slowly and with meals, than whiskey or beer; this effectively mitigates the toxic effects of alcohol. Although the issue is not clear, the current evidence favors the hypothesis that repeated heavy drinking (to the point of feeling high but not necessarily to the point of losing consciousness or motor control) leads to some cognitive deficit. The effects of alcohol on intelligence are important on a population basis for similar reasons to those of air pollutants and changes to the frequency of individuals at both ends of the IQ distribution.

Head Trauma​

Traumatic brain injury (TBI) is a particularly poignant condition, since it is largely a disease of young people. Concussion (mild TBI) is of special interest because of its prevalence (mostly from car accidents and sports); there are more than a million cases annually just in the United States. In the European Union, the overall incidence rate is 262 per 100,000 for TBI17. TBI lacks the drama of diseases like Alzheimer's, AIDS, or schizophrenia, but it is an epidemic of similar proportions. As a consequence, TBI is sometimes referred to as the "silent epidemic."

In the majority of cases, mild head injury is followed by a period of disorientation, but by a few weeks of the injury, a seemingly complete recovery occurs. There is no lasting loss of movement, language, or perception. Deficit of memory and attention may persist longer, but eventually they also disappear. Moreover, when conventional intelligence tests are given, a year or more later, major effects are often not found. When effects are found, they are usually on abstract, nonverbal reasoning tests. Tests that emphasize verbal ability appear to be much less sensitive to the aftermath of severe concussions (for important neurological reasons that should elaborated upon elsewhere[tk]). These patients are pronounced "fully recovered" and sent off to enjoy life. However, owing to the sometimes-subtle nature of neurological dysfunction, this is an instance where scores on broad intelligence tests simply fail to tell the whole story.

The Silent Epidemic​

In subtle ways, these young people are no longer their own selves. Drive, initiative, and competitive edge are often gone. They become passive and indifferent. Frequently they become inappropriately jocular, emotionally volatile, irritable, fractious, and impulsive. To an ordinary observer, these changes usually do not signal neurological impairment. However, these changes reflect subtle impairment of the executive functions, subtle dysfunction of the frontal lobes. In accordance with this notion, SPECT (functional neuroimaging) studies found that mild head trauma patients invariably have abnormal blood flow patterns—notably, blood flow in the frontal lobes is often reduced, even though CAT and MRI (structural neuroimaging) scans report normalcy. In healthy people the frontal lobes are usually more physiologically active than the rest of the cortex—neuroscientists refer to this pattern as "hyperfrontality". In certain disorders (e.g., schizophrenia) the pattern of hyperfrontality disappears and frontal lobe activity deteriorates relative to other parts of the cortex—a sure sign of severe frontal lobe dysfunction. As the seat of intentionality, foresight, and planning, the frontal lobes are the most uniquely “human” of all the components of the human brain. Being a conductor in the orchestra that is the brain requires many connections to myriad distinct components. The crucial consequences of this are illustrated in the following excerpt18:

...the frontal lobes are more vulnerable and are affected in a broader range of brain disorders—neurodevelopmental, neuropsychiatric, neurogeriatric, and so on—than any other part of the brain. The frontal lobes have an exceptionally low "functional breakdown threshold." This led me many years ago to conclude that frontal lobe dysfunction is to brain disease what fever is to bacterial infection; it is both highly predictable and often nonspecific. The frontal lobes’ unique vulnerability is the price they pay for the exceptional richness of their connections.

This has vast implications on the etiology and epidemiology of ADHD[tk], a particular interest among users of r/cognitivetesting. More information about the role of the frontal lobes in cognition can be found in the [tk] section.

Furthermore, when patients are tested using laboratory tasks or neuropsychology tests that evaluate working memory functions, effects are often found. These tasks are considerably more sensitive than the memory evaluations included in most intelligence tests. Injured people often do not report problems in everyday life, even if they have trouble with the laboratory tasks. It would be wrong to conclude on the basis of intelligence tests alone that the residual effects of concussion are not serious enough to be of concern.

A study showed how concussion can act as a distal influence that increases the risk of incurring a condition that acts as a proximal influence on intelligence. The people studied were elderly pairs of twins (over sixty years), where one twin suffered from Parkinson’s disease, which can result in a loss of intelligence in the latter stages, and the other did not (discordant twins). The risk of incurring Parkinson’s disease tripled for those who had experienced head injuries, even though the head injuries had occurred, on average, thirty-seven years before the study was conducted19.

The news emanating from this understanding is both good and bad. The bad news is that the prevalence of lasting impairment following even "mild" head trauma is higher than had been thought. Almost invariably, the impairment affects frontal lobe functions. The good news is that identifying the cause is the first step toward developing effective therapies and pharmacology is ever-evolving.

Key points​

  • Undernutrition occurring for the first time in older children seems to have no permanent effect on intelligence.
  • In terms of IQ improvement, vitamin and mineral supplements are only beneficial when they remedy an existing deficiency.
  • Iodine supplementation during pregnancy or infancy can raise average IQs in the worst-off regions by 12 IQ points
  • Creatine administration may improve short-term memory and intelligence/reasoning in healthy individuals. Administration benefits are surefire in aging and sleep-deprived individuals.
  • The current evidence favors the hypothesis that repeated heavy drinking (to the point of feeling high but not necessarily to the point of losing consciousness or motor control) leads to some cognitive deficit.
  • If we were to restrict ourselves to the intelligence test data and superficial observation alone, we erronously conclude that a knock on the head is not all that serious. The fact of the matter is, losses of cognitive functions and executive function can occur when the brain is subjected to apparently minor physical damage.

Citations​

Footnotes​

  1. https://pmc.ncbi.nlm.nih.gov/articles/PMC5987539/ ↩

  2. Stoch, M. B., & Smythe, P. M. Does undernutrition during infancy inhibit brain growth and subsequent intellectual development? Arch. Dis. Childh., 1963, 38, 546-552. ↩

  3. Nelson, G. K., & Dean, R. F. A. Bull. World Health Organ., 1959, 21, 779. Cited by G . Cravioto, Malnutrition and behavioral development in the preschool child. Pre-school child malnutrition. National H ealth Science, 1966, Public. No. 1282. ↩

  4. Stein, Z., Susser, M., Saenger, G., & Marolla, F. 1972. Nutrition and mental performance. Science, 178, 708–713. ↩

  5. https://psycnet.apa.org/record/1998-04015-005 ↩

  6. https://slatestarcodex.com/Stuff/guatemala.pdf ↩

  7. https://pmc.ncbi.nlm.nih.gov/articles/PMC6919660/ ↩ ↩2

  8. https://gwern.net/doc/iodine/2005-qian.pdf ↩

  9. https://pmc.ncbi.nlm.nih.gov/articles/PMC6093191/ ↩

  10. https://pmc.ncbi.nlm.nih.gov/articles/PMC5736171/ ↩ ↩2

  11. https://journals.sagepub.com/doi/10.1111/j.1529-1006.2005.00024.x ↩

  12. https://pmc.ncbi.nlm.nih.gov/articles/PMC1257652/ ↩

  13. https://linkinghub.elsevier.com/retrieve/pii/S0065310114000164 ↩

  14. https://pubmed.ncbi.nlm.nih.gov/11524299/ ↩

  15. https://pubmed.ncbi.nlm.nih.gov/1875711/ ↩

  16. https://pubmed.ncbi.nlm.nih.gov/16185206/ ↩

  17. https://pubmed.ncbi.nlm.nih.gov/26269030/ ↩

  18. Elkhonon Goldberg. The New Executive Brain: Frontal Lobes in a Complex World, NY: Oxford University Press, 2009. ISBN 978-0-19-532940-7 ↩

  19. https://pubmed.ncbi.nlm.nih.gov/16718702/ ↩

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