Health and intelligence

Health and intelligence are two closely-related aspects of human well-being. The impact of health on intelligence is one of the most important factors in understanding 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 organochlorides). Comprehensive policy recommendations targeting reduction of cognitive impairment in children have been proposed.Olness, K. " [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&list_uids=12692458&dopt=Citation Effects on brain development leading to cognitive impairment: a worldwide epidemic] ," "Journal of Developmental and Behavioral Pediatrics" 24, no. 2 (2003): 120–30.] cite book |last=Perlmutter |first=David |authorlink=David Perlmutter (neurologist) |coauthors=Carol Colman |title=Raise a Smarter Child By Kindergarten: Raise Iq Points By Up to 30 Points and Turn on Your Child's Smart Genes Points |year=2006 |publisher=Morgan Road Books |isbn=978-0767923019 ]

Improvements in nutrition, and in public policy in general, have been implicated in worldwide IQ increases (the Flynn effect).

Nutrition

Malnutrition may occur during several different periods of growth, such as pregnancy, 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.

Timing

Although some observers have argued that the first six months of life are the most critical in the sense that malnutrition during that time period harms cognitive development more than malnutrition later in life, a study from the Philippines argue that malnutrition in the second year of life may have a larger negative impact than malnutrition in the first year of life. [ [http://wber.oxfordjournals.org/cgi/content/abstract/15/1/81 The Impact of Early Childhood Nutritional Status on Cognitive Development: Does the Timing of Malnutrition Matter?] Paul Glewwe and Elizabeth M. King THE WORLD BANK ECONOMIC REVIEW, VOL. 15, NO. 1, 81-113]

Intrauterine growth retardation

Undernutrition during pregnancy, and other factors, may cause intrauterine growth retardation (IUGR), which is one cause of low birth weight. 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 not 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 SES, whereas after the famine, there was a compensatory increase in births among the those with lower SES. Since SES correlates with IQ, this may have hidden an effect caused by the undernutrition. [ [http://www.unu.edu/unupress/food2/UID03E/uid03e00.htm#Contents Causes and Consequences of Intrauterine Growth Retardation] European Journal of CLINICAL NUTRITION Volume 52, Supplement 1, January 1998.Cite web |url=http://www.lrainc.com/swtaboo/taboos/apa_01.html|title=Intelligence: Knowns and Unknowns|accessmonthday=August 6 |accessyear=2006|date=August 7, 1995|author=Neisser "et al."|publisher=Board of Scientific Affairs of the American Psychological Association]

Breastfeeding

The longstanding belief that breastfeeding correlates with 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. The results of this study argued that prior studies had not allowed 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. [Cite web
url=http://bmj.bmjjournals.com/cgi/rapidpdf/bmj.38978.699583.55v1
title= Effect of breast feeding on intelligence in children: prospective study, sibling pairs analysis, and meta-analysis
accessmonthday= |accessyear=
date=2006
author= Geoff Der, G David Batty, Ian J. Deary
publisher= British Medical Journal
format=Abstract] The study has been subject to various criticisms. [ [http://www.scireview.de/violence/prescott/letters/bmj_Responses.pdf Rapid Responses] ] Another study found a positive effect of breastfeeding also after controlling for parental IQ. [ [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=15494884&query_hl=1&itool=pubmed Influence of breast-feeding and parental intelligence on cognitive development in the 24-month-old child.] Clin Pediatr (Phila). 2004 Oct;43(8):753-61. Influence of breast-feeding and parental intelligence on cognitive development in the 24-month-oldGomez-Sanchiz M, Canete R, Rodero I, Baeza JE, Gonzalez JA.] Another study concluded that breastfeeding increases 8.3 points in IQ on average. [ Masters, R. (1997). Brain biochemistry and social status: The neurotoxicity hypothesis. InE. White (Ed.), Intelligence, political inequality, and public policy (pp. 141–183).Westport, CT: Praeger.]

A study shows that breastmilk can raise IQ by 7 points if the infants had a "C" version of the FADS2 gene. Those with the "G" version have no IQ advantage. [ [http://www.dukenews.duke.edu/2007/11/breastIQ.html Baby's IQ Raised by Breastmilk and Genes ] ] cite journal |author=Caspi A, Williams B, Kim-Cohen J, "et al" |title=Moderation of breastfeeding effects on the IQ by genetic variation in fatty acid metabolism |journal= |volume= |issue= |pages= |year=2007 |pmid=17984066 |doi=10.1073/pnas.0704292104]

Infancy

Two studies in Chile on 18 years old high-school graduates found that nutritional status during the first year of life affected IQ, scholastic achievement, and brain volume. [D.M. Ivanovic et al., " [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11895316&dopt=Citation Nutritional status, brain development and scholastic achievement of Chilean high-school graduates from high and low intellectual quotient and socio-economic status] ," "British Journal of Nutrition" 87, no. 1 (January 2002): 81–92; D.M. Ivanovic et al., " [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=15093150&dopt=Citation Head size and intelligence, learning, nutritional status and brain development. Head, IQ, learning, nutrition and brain] ," "Neuropsychologia" 42, no. 8 (2004): 1118–31.]

Micronutrients and vitamin deficiencies

Micronutrient deficiencies (e.g. in iodine and iron) influence the development of intelligence and remain a problem in the developing world.

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. [Behrman, J.R., Alderman, H., and Hoddinott, J., " [http://www.copenhagenconsensus.com/Files/Filer/CC/Papers/sammendrag/Accepted__Hunger_summary_070504.pdf Hunger and Malnutrition] ," Copenhagen Consensus 2004.]

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." [UNICEF and The Micronutrient Initiative, " [http://www.micronutrient.org/reports/reports/Full_e.html Vitamin & Mineral Deficiency: A Global Progress Report] ," March 2004.]

Overall, studies investigating whether cognitive function in already iron-deficient children can be improved with iron supplements have produced mixed results, possible because deficiency in critical growth periods may cause irreversible damage. However, several studies with better design have shown substantial benefits. In order to prevent iron deficiency an option is giving specific supplementation, 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. [Saloojee, H. and Pettifor, J., [http://bmj.bmjjournals.com/cgi/content/full/323/7326/1377 Iron deficiency and impaired child development] ," "BMJ" 323 (December 2001): 1377–78] Developed nations fortify several foods with various micronutrients. [ [http://www.fao.org/docrep/W2840E/w2840e03.htm FOOD FORTIFICATION TECHNOLOGY] Food Fortification: Technology and Quality Control. (FAO Food And Nutrition Paper - 60)]

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 years old children in the United States for 3 months found an average increase 2 to 3 IQ points. Most of this can explained by the very large increase for 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. [ [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10706232 The effect of vitamin-mineral supplementation on the intelligence of American schoolchildren: a randomized, double-blind placebo-controlled trial] J Altern Complement Med. 2000 Feb;6(1):31-5.]

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. [Helland IB, Smith L, Saarem K, Saugstad OD, Drevon CA. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12509593&dopt=Abstract Maternal supplementation with very-long-chain n-3 fatty acids during pregnancy and lactation augments children's IQ at 4 years of age.] "Pediatrics". 2003 Jan;111(1):e39-44.] Vitamin B12 and folate may be important for cognitive function in old age. [Duthie SJ, Whalley LJ, Collins AR, Leaper S, Berger K, Deary IJ. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11976166&dopt=Citation Homocysteine, B vitamin status, and cognitive function in the elderly.] "Am J Clin Nutr". 2002 May;75(5):908-13. Erratum in: "Am J Clin Nutr". 2003 Feb;77(2):523.]

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. [Lyketsos, Constantine G, "Should pregnant women avoid eating fish? Lessons from the Seychelle," "The Lancet", Volume 361, Issue 9370 , 17 May 2003, Pages 1667-1668 doi|doi:10.1016/S0140-6736(03)13379-X] [ [http://www.msnbc.msn.com/id/17177330/site/newsweek/ Pregnant Women: Eat More Fish or Not? - To Your Health - MSNBC.com ] ] [ [http://www.physorg.com/news90840782.html Fish Diet in Pregnancy May Hone Kids' IQ ] ] [ [http://www.economist.com/science/PrinterFriendly.cfm?story_id=5407595 Diet and the unborn child | The omega point | Economist.com ] ] [ [http://www.medpagetoday.com/OBGYN/Pregnancy/tb1/5075 Medical News: Eating Fish During Pregnancy Provides 'Brain Food' for Child - in OB/GYN, Pregnancy from MedPage Today ] ] [ [http://www.webmd.com/baby/news/20040716/pregnant-omega-3-essential-for-babys-brain Pregnant? Omega-3 Essential for Baby's Brain ] ]

Protein and energy malnutrition

One study from developing country, Guatemala, found that poor growth during infancy, rather than low birth weight, was negatively related to adolescent performance on cognitive and achievement tests. [Pollitt E, Gorman KS, Engle P, Martorell R and Rivera JA, 1993. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8272081&dopt=Citation Early Supplementary Feeding and Cognition: Effects Over Two Decades] Monographs of the Society for Research in Child Development, Serial No. 235, 58(7): 122 pages.] A later related very long term study looked at the effect of giving 6-24 months 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. [ Schooling, educational achievement, and cognitive functioning among young Guatemalan adults. Food Nutr Bull. 2005 Jun;26(2 Suppl 1):S46-54. Stein AD, Behrman JR, DiGirolamo A, Grajeda R, Martorell R, Quisumbing A, Ramakrishnan U.]

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). [ [http://earthtrends.wri.org/searchable_db/results.php?years=1996-2004&variable_ID=2128&theme=4&cID=&ccID=0,1,6,3,5,7,4,10,13,12 Children's Health: Stunting in children under 5-moderate and severe ] ] The prevalence was even higher previously since the worldwide prevalence of stunting is declining by about half of a percentage point each year. [ [http://www.news.cornell.edu/releases/May98/stunting.ssl.html Stunted growth affects almost 40 percent of the developing world's infants, Cornell study reports] ] A study on stunted children aged 9-24 months in Jamaica 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. [ [http://www.cababstractsplus.org/google/abstract.asp?AcNo=20053208746 Effects of early childhood psychosocial stimulation and nutritional supplementation on cognition and education in growth-stunted Jamaican children: prospective cohort study] Lancet (British edition), 2005 (Vol. 966) (No. 9499) 1804-1807. Walker, S. P., Chang, S. M., Powell, C. A., Grantham-McGregor, S. M.] [ [http://www.bmj.com/cgi/content/abstract/333/7566/472 Effects of psychosocial stimulation and dietary supplementation in early childhood on psychosocial functioning in late adolescence: follow-up of randomised controlled trial] Susan P Walker, professor1, Susan M Chang, lecturer1, Christine A Powell, senior lecturer1, Emily Simonoff, professor2, Sally M Grantham-McGregor, professor3. BMJ 2006;333:472 (2 September), doi:10.1136/bmj.38897.555208.2F (published 28 July 2006)]

Toxins

Industrial chemicals

Certain toxins, such as lead, mercury, 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. [ [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Abstract&list_uids=17174709 Developmental neurotoxicity of industrial chemicals] . Lancet. 2006 Dec 16;368(9553):2167-78. Grandjean P, Landrigan PJ.]

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.Meyer, P.A., McGeehin, M.A., and Falk, H. " [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12971691&dopt=Citation A global approach to childhood lead poisoning prevention] ," "International Journal of Hygiene and Environmental Health" 206, nos. 4–5 (August 2003): 363–69.] Even slightly elevated lead levels around the age of 24 months are associated with intellectual and academic performance deficits at age 10 years. [ [http://pediatrics.aappublications.org/cgi/content/abstract/90/6/855 Low-Level Lead Exposure, Intelligence and Academic Achievement: A Long-term Follow-up Study] David C. Bellinger PhD, MSc1, Karen M. Stiles PhD, MN1, and Herbert L. Needleman MD1. PEDIATRICS Vol. 90 No. 6 December 1992, pp. 855-861 ]

Certain, at least previously, widely used organochlorides, such as dioxins, DDT, and PCB, have been associated with cognitive deficits. [ [http://aje.oxfordjournals.org/cgi/content/abstract/164/10/955 In Utero Exposure to Background Concentrations of DDT and Cognitive Functioning among Preschoolers] Núria Ribas-Fitó1, Maties Torrent2, Daniel Carrizo3, Laura Muñoz-Ortiz1, Jordi Júlvez1, Joan O. Grimalt3 and Jordi Sunyer1 American Journal of Epidemiology 2006 164(10):955-962]

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. [ [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Abstract&list_uids=17174709 Developmental neurotoxicity of industrial chemicals] . Lancet. 2006 Dec 16;368(9553):2167-78. Grandjean P, Landrigan PJ. ] An appendix listed furher industrial chemicals considered to be neurotoxic. [ [http://www.hsph.harvard.edu/neurotoxicant/appendix.doc Potentials for exposure to industrial chemicals suspected of causing developmental neurotoxicity] Philippe Grandjean, MD, PhD, Adjunct Professor Marian Perez, MPH, Project Coordinator Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA ]

Recreational drugs

Current cannabis 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 foetal development are minimal when compared with the well-documented adverse effects of tobacco or alcohol use. [ [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=15661628&dopt=Citation Long-term effects of exposure to cannabis.] Iversen L. Curr Opin Pharmacol. 2005 Feb;5(1):69-72.]

Fetal alcohol exposure, causing Fetal alcohol syndrome, is one of the leading known causes of mental retardation in the Western world. [Abel, E.L., & Sokel, R.J. (1987). Incidence of fetal alcohol syndrome and economic impact of FAS-related anomalies: Drug alcohol syndrome and economic impact of FAS-related anomalies. "Drug and Alcohol Dependency", "19(1)", 51-70.]

Maternal tobacco smoking during pregnancy is associated with increased activity, decreased attention, and diminished intellectual abilities. [ [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12009494&dopt=Abstract The effects of tobacco exposure on children's behavioral and cognitive functioning: implications for clinical and public health policy and future research.] Weitzman M, Byrd RS, Aligne CA, Moss M. Neurotoxicol Teratol. 2002 May-Jun;24(3):397-406.] 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. [ [http://ije.oxfordjournals.org/cgi/content/abstract/34/5/1047 Maternal smoking during pregnancy and offspring IQ] Naomi Breslau1,*, Nigel Paneth1, Victoria C Lucia1 and Rachel Paneth-Pollak2 International Journal of Epidemiology 2005 34(5):1047-1053 ] 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. [ [http://www.pubmedcentral.nih.gov/botrender.fcgi?blobtype=html&artid=1253717 Exposure to Environmental Tobacco Smoke and Cognitive Abilities among U.S. Children and Adolescents] Kimberly Yolton, Kim Dietrich, Peggy Auinger, Bruce P. Lanphear, and Richard Hornung1. Environ Health Perspect. 2005 January; 113(1): 98–103.]

Cosmetics

The use of some skin whitening products, unusually popular amongst Asian women,In a survey, 28% of Koreans and 50% of Philippians say that they use skin whitening products. Citation
title=Skin lightening in Asia? A bright future?
url=http://www.synovate.com/knowledge/infact/issues/200406/] has detrimental effects toward IQ.Skin whitening products, often contain toxic chemicals, such as mercury and hydroquinone, as the active ingredient.Citation
title=Whitening skin can be deadly
last=Counter
first=S. Allen
publisher=The Boston Globe
url=http://www.boston.com/news/globe/health_science/articles/2003/12/16/whitening_skin_can_be_deadly/
date=December 16, 2003] Citation
title=New York City Warns: Some Skin Creams Are Poisonous
last=Heyward
first=Georgia
publisher=The Epoch Times
url=http://en.epochtimes.com/news/5-2-5/26302.html
date=February 5, 2005] Citation
title=Mercury in Cosmetic Skin Whitening Creams
url=http://www.hgtech.com/Data/Other/Hg%20Cream.htm] A major portion skin whitening products, especially popular sold in stores around Asia, have been criticized by many, such as the FDA, for the presence of these toxic chemicals.Citation
title=FDA Proposes Hydroquinone Ban
url=http://www.medicinenet.com/script/main/art.asp?articlekey=64167 FDA bans hydroquinone in skin whitening products] Citation
title=Skin-lightening creams face FDA ban: Dermatologists defend treatment
url=http://findarticles.com/p/articles/mi_qn4155/is_20070128/ai_n17159064 FDA bans hydroquinone in skin whitening products] Citation
title=NYC HEALTH DEPT. WARNS AGAINST USE OF "SKIN-LIGHTENING" CREAMS CONTAINING MERCURY OR SIMILAR PRODUCTS WHICH DO NOT LIST INGREDIENTS
date=January 27, 2005
url=http://www.nyc.gov/html/doh/html/pr/pr008-05.shtml] When applied, mercury and hydroquinone absorbs through the skin into bloodstream. Studies shown that an increase in 100 micrograms of mercury in blood decreases IQ by an average of 14 points in children. The effects of mercury poisoning and hydroquinone poisoning, such severe mental and physical disorders have resulted from the use of mercury-containing and hydroquinone-containing cosmetic products, including skin-whitening products.Citation
title=Skin Lightening
url=http://www.cosmeticscop.com/learn/art.asp?ID=157 Article that links skin whitening products to mercury and hydroquinone] cite journal
title=Mercury exposure in children: a review
last=Countera
first=S. Allen
coauthors=Leo H. Buchanan
url=http://www.state.nj.us/health/eoh/cehsweb/kiddiekollege/documents/counter04_mercuryexpochildren.pdf] cite journal
title=The Toxicology of Mercury and Its Chemical Compounds
author=Clarkson
coauthors=Thomas, Magos, Laszlo
url=http://www.ingentaconnect.com/content/tandf/btxc/2006/00000036/00000008/art00001?crawler=true] Citation
title=Dynamics of Mercury Pollution on Regional and Global Scales
last=Mahaffey
first=Kathryn R.
url=http://www.springerlink.com/content/w245027uu23r4381/] The use of skin whitening products is especially popular in Hong Kong.Citation
title=SKIN DEEP: Dying to be white
last=Bray
first=Marianne
publisher=CNN
url=http://edition.cnn.com/2002/WORLD/asiapcf/east/05/13/asia.whitening/] However, a majority of products sold there are cited by Hong Kong officials to contain mercury as its active ingredient, often 27,000 to 60,000 times the "acceptable" dose. Skin whitening products, which a majority sold in Asian nations contain mercury or hydroquinone, are also very harmful to the brain development of fetuses in pregnant women.Citation
title=Asian Skin Tanning Article
url=http://www.chinatownconnection.com/asian_skin_tanning.htm An argument that links skin whitening products to the development of the brain of a fetus of pregnant Asian women, both mercury and hydroquinone. Therefore it is not ] Citation
title=Mercury Fact Sheet
url=http://www.zeromercury.org/fact_sheet/index.htm Another argument that links skin whitening products to the development of the brain of a fetus of pregnant Asian women. Therefore it is not ] Citation
title=DOES LOW MERCURY CONTAINING IN-LIGHTENING CREAM (FAIR & LOVELY) EFFECT THE KIDNEY, LIVER, AND BRAIN OF FEMALE MICE?
url=http://www.informaworld.com/smpp/content~content=a713930964~db=all Another argument that links skin whitening products to the development of the brain of a fetus of pregnant Asian women, both mercury and hydroquinone. Therefore it is not ] cite journal | author = Yang MG, Krawford KS, Garcia JD, Wang JH, Lei KY | title = Deposition of mercury in fetal and maternal brain | journal = Proc. Soc. Exp. Biol. Med. | volume = 141 | issue = 3 | pages = 1004–7 | year = 1972 | pmid = 4645746 | doi = ] cite journal |author=Shafiq-ur-Rehman, Rehman S, Chandra O, Abdulla M |title=Evaluation of malondialdehyde as an index of lead damage in rat brain homogenates |journal=Biometals |volume=8 |issue=4 |pages=275–9 |year=1995 |pmid=7580048 |doi=]

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 meningitis, 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.

Stress

A recent theory suggests that early childhood stress may affect the developing brain and cause negative effects. ["How similar are fluid cognition and general intelligence? A developmental neuroscience perspective on fluid cognition as an aspect of human cognitive ability", Behavioral and Brain Sciences (2006), 29: 109-125 Cambridge University Press, Clancy Blair. Multiple comments can be seen on [http://scholar.google.se/scholar?as_q=&num=10&btnG=S%C3%B6k+Scholar&as_epq=How+similar+are+fluid+cognition+and+general+intelligence&as_oq=&as_eq=&as_occt=any&as_sauthors=&as_publication=Behavioral+and+Brain+Sciences&as_ylo=&as_yhi=&as_allsubj=all&hl=sv&lr= Google Scholar.] ] Exposure to violence in childhood has been associated with lower school grades" [http://archpedi.ama-assn.org/cgi/content/abstract/156/3/280 Violence Exposure, Trauma, and IQ and/or Reading Deficits Among Urban Children] " Virginia Delaney-Black, MD, MPH; Chandice Covington, PhD, RN, CPNP; Steven J. Ondersma, PhD; Beth Nordstrom-Klee, PhD; Thomas Templin, PhD; Joel Ager, PhD; James Janisse, PhD; Robert J. Sokol, MD Vol. 156 No. 3, March 2002] and lower IQ in children of all races. [http://www.springerlink.com/content/p56w670331216805/ IQ and Posttraumatic Stress Symptoms in Children Exposed to Interpersonal Violence] ] A group of largely African American urban first-grade children and their caregivers were evaluated using self-report, interview, 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. [ [http://www.springerlink.com/content/9387678780625375/ Family, peer, and neighborhood influences on academic achievement among African-American adolescents: One-year prospective effects] ]

Tropical infectious diseases

On the disease front, malaria 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. [Boivin, M.J., " [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12394524&dopt=Citation Effects of early cerebral malaria on cognitive ability in Senegalese children] ," "Journal of Developmental and Behavioral Pediatrics" 23, no. 5 (October 2002): 353–64. Holding, P.A. and Snow, R.W., " [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11425179&dopt=Citation Impact of Plasmodium falciparum malaria on performance and learning: review of the evidence] ," "American Journal of Tropical Medicine and Hygiene" 64, suppl. nos. 1–2 (January–February 2001): 68–75.] 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. [ [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9100486&dopt=Citation "Stupidity or worms": do intestinal worms impair mental performance?] Watkins WE, Pollitt E. Psychol Bull. 1997 Mar;121(2):171-91]

Association with other diseases

There are numerous diseases affecting the central nervous system 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 brain. Others may affect many other organs, like HIV, Hashimoto's thyroiditis causing hypothyroidism, or cancer.

Persons with a higher IQ have generally lower adult morbidity and mortality. This may be because they better avoid injury and take better care of their own health, or alternatively may be due to a slight increased propensity for material wealth. Post-Traumatic Stress Disorder, severe depression, and schizophrenia are less prevalent in higher IQ bands. The "Archive of General Psychiatry" published a longitudinal study of a randomly selected sample of 713 study participants (336 boys and 377 girls), from both urban and suburban settings. Of that group, nearly 76 percent had suffered through at least one traumatic event. Those participants were assessed at age 6 years and followed up to age 17 years. In that group of children, those with an IQ above 115 were significantly less likely to have Post-Traumatic Stress Disorder as a result of the trauma, less likely to display behavioral problems, and less likely to experience a trauma. The low incidence of Post-Traumatic Stress Disorder among children with higher IQs was true even if the child grew up in an urban environment (where trauma averaged three times the rate of the suburb), or had behavioral problems. [Cite web
url=http://archpsyc.ama-assn.org/cgi/content/abstract/63/11/1238
title= Intelligence and Other Predisposing Factors in Exposure to Trauma and Posttraumatic Stress Disorder. A Follow-up Study at Age 17 Years
accessmonthday=August 6 |accessyear=2006
date=11, November 2006
author= Naomi Breslau, PhD; Victoria C. Lucia, PhD; German F. Alvarado, MD, MPH
publisher= Arch Gen Psychiatry. 2006;63:1238-1245] On the other hand, higher IQ shows a higher prevalence of those conditioned with Obsessive Compulsive Disorder. [Cite web
url=http://www.loni.ucla.edu/~thompson/PDF/GT_DM_5b.pdf
title=GT_DM_5b.pdf
accessmonthday= |accessyear=
date=
author=
publisher=
format=PDF]

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. [ [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1572949&dopt=Citation Effects of major depression on estimates of intelligence] Sackeim HA, Freeman J, McElhiney M, Coleman E, Prudic J, Devanand DP. J Clin Exp Neuropsychol. 1992 Mar;14(2):268-88.] [ [http://www.blackwell-synergy.com/doi/abs/10.1111/j.1440-1819.2006.01564.x Improvement of cognitive functioning in mood disorder patients with depressive symptomatic recovery during treatment: An exploratory analysis] LAURA MANDELLI, Psy. D, ALESSANDRO SERRETTI, md,1 CRISTINA COLOMBO, md, MARCELLO FLORITA, Psy. D, ALESSIA SANTORO, Psy. D, DAVID ROSSINI, MD, RAFFAELLA ZANARDI, MD AND ENRICO SMERALDI, MD. Psychiatry and Clinical Neurosciences Volume 60 Issue 5 Page 598 - October 2006]

Research in Scotland has shown that a 15-point lower IQ meant people had a fifth less chance of seeing their 76th birthday, while those with a 30-point disadvantage were 37% less likely than those with a higher IQ to live that long. [Cite web
url=http://www.bmj.com/cgi/content/abstract/322/7290/819
title=Longitudinal cohort study of childhood IQ and survival up to age 76
accessmonthday=August 6 |accessyear=2006
date=2001
author=Whalley and Deary
publisher=British Medical Journal 2001, 322:819-819] In addition, a study of 11,282 individuals in Scotland who took intelligence tests at ages 7, 9 and 11 in the 1950s and 1960s, found an "inverse linear association" between childhood intelligence and hospital admissions for injuries in adulthood. The association between childhood IQ and the risk of later injury remained even after accounting for factors such as the child's socioeconomic background. [Cite web
url=http://www.ajph.org/cgi/content/abstract/AJPH.2005.080168v1
title=Associations Between Childhood Intelligence and Hospital Admissions for Unintentional Injuries in Adulthood: The Aberdeen Children of the 1950s Cohort Study
accessmonthday=January 10 |accessyear=2007
date=2006
author= Debbie A. Lawlor, University of Bristol, Heather Clark, University of Aberdeen, David A. Leon, London School of Hygiene & Tropical Medicine
publisher=American Journal of Public Health, December 2006]

A decrease in IQ has also been shown as an early predictor of late-onset Alzheimer's Disease and other forms of dementia. In a 2004 study, Cervilla and colleagues showed that tests of cognitive ability provide useful predictive information up to a decade before the onset of dementia. [Cite web
url=http://www.jnnp.com/cgi/content/abstract/75/8/1100
title= Premorbid cognitive testing predicts the onset of dementia and Alzheimer's disease better than and independently of APOE genotype
accessmonthday=August 6 |accessyear=2006
date=2004
author=Cervilla et al
publisher=Psychiatry 2004;75:1100-1106.]

However, when diagnosing individuals with a higher level of cognitive ability, in this study those with IQ's of 120 or more, [Cite web
url=http://laboratory-manager.advanceweb.com/common/editorial/editorial.aspx?CC=27318
title= More Sensitive Test Norms Better Predict Who Might Develop Alzheimer's Disease
accessmonthday=August 6 |accessyear=2006
date=
author= Dorene Rentz, Brigham and Women's Hospital's Department of Neurology and Harvard Medical School
publisher= Neuropsychology, published by the American Psychological Association ] patients should not be diagnosed from the standard norm but from an adjusted high-IQ norm that measured changes against the individual's higher ability level.

In 2000, Whalley and colleagues published a paper in the journal "Neurology", which examined links between childhood mental ability and late-onset dementia. The study showed that mental ability scores were significantly lower in children who eventually developed late-onset dementia when compared with other children tested. [Cite web
url=http://www.neurology.org/cgi/content/abstract/55/10/1455
title= Childhood mental ability and dementia
accessmonthday=August 6 |accessyear=2006
date=2000
author=Whalley "et al."
publisher=Neurology 2000;55:1455-1459.]

ee also

* Health and race
* Race and height
* Intelligence quotient
* Neuroscience and intelligence

References