Editing Intelligence quotient (section)

==Health==
{{Main|Impact of health on intelligence|Cognitive epidemiology}}
Health is important in understanding 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, or sometimes be partially or wholly compensated for by later growth.<ref>{{Cite journal |last1=Buss |first1=Claudia |last2=Entringer |first2=Sonja |last3=Swanson |first3=James M. |last4=D. Wadhwa |first4=Pathik |date=2012 |title=The Role of Stress in Brain Development: The Gestational Environment's Long-Term Effects on the Brain |journal=Cerebrum |volume=4 |page=4 |pmid=23447790 |pmc=3574809 }}</ref>

Since about 2010, researchers such as Eppig, Hassel, and MacKenzie have found a very close and consistent link between IQ scores and infectious diseases, especially in the infant and preschool populations and the mothers of these children.<ref name=":7">Eppig. Christopher. Scientific American."Why is average IQ higher in some places?" 2011.</ref> They have postulated that fighting infectious diseases strains the child's metabolism and prevents full brain development. Hassel postulated that it is by far the most important factor in determining population IQ. However, they also found that subsequent factors such as good nutrition and regular quality schooling can offset early negative effects to some extent.

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<ref>{{Cite journal |last1=Olson |first1=Rebecca |last2=Gavin-Smith |first2=Breda |last3=Ferraboschi |first3=Chiara |last4=Kraemer |first4=Klaus |date=April 2021 |title=Food Fortification: The Advantages, Disadvantages and Lessons from Sight and Life Programs |journal=Nutrients |volume=13 |issue=4 |pages=1118 |doi=10.3390/nu13041118 |pmid=33805305 |pmc=8066912 |doi-access=free }}</ref> and laws establishing safe levels of pollutants (e.g. [[lead]], [[Mercury (element)|mercury]], and organochlorides). Improvements in nutrition, and in public policy in general, have been implicated in IQ increases.<ref>{{Cite news |last=Nisen |first=Max |date=July 22, 2013 |title=How Adding Iodine To Salt Resulted In A Decade's Worth Of IQ Gains For The United States |work=Business Insider |url=https://www.businessinsider.com/iodization-effect-on-iq-2013-7#ixzz2ZuFjmyY7 |access-date=December 16, 2023}}</ref>

[[Cognitive epidemiology]] is a field of research that examines the associations between intelligence test scores and health. Researchers in the field argue that intelligence measured at an early age is an important predictor of later health and mortality differences.{{sfn|Deary|Batty|2007}}