Sex differences in the relationship of dietary fatty acids to cognitive measures in American children

Because the first neurons evolved in an environment high in the n3 (omega 3) fatty acid docosahexaenoic acid (DHA), this fatty acid became a major component of neural structure and function and makes up 10% of the dry weight of the human brain. Since n3 fatty acids must come from the diet, this suggests a possible positive role for dietary n3 fatty acids in cognition and a possible negative role for n6 fatty acids, which compete with n3 for access to critical enzymes. Because human females must provide DHA for the growth of the unusually large brains of their offspring from maternal fat stored  during childhood, their need for DHA is especially great. We used stepwise regression to determine whether particular dietary fatty acids and other nutrients were related to cognitive performance in over 4000American children aged 6 to 16 from the Third National Health and Nutrition Examination Survey; a variety of possible biological, social, and environmental risk factors were statistically controlled. In this context the only dietary factors related to cognitive performance were n3 and n6 fatty acids. Dietary n3 fatty acids were positively related to cognitive test scores in male and female children, while n6 showed the reverse relationship, significantly so in females. In female children the positive effects of n3 intake were twice as strong as in males and exceeded the negative effects of lead exposure. This suggests that increasing dietary intake of n3 and decreasing n6 fatty acids may have cognitive benefits in children, especially in females.  (Authors abstract)
DHA plays a critical positive role in all aspects of neuronal growth, synaptic connections, and functioning. Animal studies show that a deficiency of dietary n3 fatty acids leads to a decrease in neuronal size and synapse number and impaired learning ability. Many studies in human infants have shown that levels of DHA in the maternal diet or blood during pregnancy and in maternal milk or formula are positively related to cognitive and visual development in infants. Using a large sample drawn from NHANES III, dietary n3 fatty acids were shown to be positively related to cognitive performance in children 6 to 16 years of age, while n6 fatty acids are negatively related to cognitive performance in females in the same sample. As predicted, the contribution of dietary n3 to cognitive performance is much greater (two-fold) in females, and females also show a significant negative effect for n6 fatty acids which compete with n3 for enzymes needed in the biosynthesis of DHA. The stronger effect of n3 and significantly negative effect of n−6 in girls may reflect their greater need for n3 fatty acids to sustain future pregnancy and lactation, as explained above. Because stored maternal fat is selectively used to support the development of the fetal and infant brain via the placenta and breast milk, females must prepare for these demands by storing DHA in fat at a much higher rate than males during their childhood and adolescence, while their own brains and bodies are still growing. This competition between growth and reproductive goals, absent in boys, may make girls more subject to the antagonism between the n6 and n3 fatty acid families in commandeering necessary synthetic enzymes. These findings on the relationship between dietary fatty acids and cognitive performance are of particular interest in relation to current American food consumption patterns. The cognitive effects of dietary fatty acids in American children may be greater than in other populations because of the limited amount of n3 fatty acids in the American diet combined with unusually high levels of n6. (Editors Comments)