Health can affect intelligence in various ways. Conversely, intelligence can affect health. Health effects on intelligence have been described as being among the most important factors in 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 of the child 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.