Food supplement use is widely promoted, but little is known about the cognitive effects of food supplements.

We examined the effects of food supplement use on cognitive aging.

This was an observational study of subjects born in 1936 whose mental ability was tested in 1947 and who were followed up in 2000-2001, at which time cognition, diet, food supplement use, and risk factors for vascular disease were assessed.
In a nested case-control study, fish-oil users were matched with nonusers, and cognitive function was related to erythrocyte n-3 fatty acid composition.

Childhood intelligence quotient (IQ) did not differ significantly by category of food supplement use (ie, none, fish oil, vitamins, and other).

At the age of 64 y, cognitive function was higher in food supplement users than in nonusers before adjustment for childhood IQ. After adjustment for childhood IQ, digit symbol (mental speed) test scores were higher in food supplement users.

Fish-oil supplement users consumed more vitamin C and vegetable and cereal fiber than did non-supplement-users. In a nested case-control study, erythrocyte membrane n-3 content was higher in fish-oil supplement users than in nonusers, but cognitive function did not differ significantly between groups.

Total erythrocyte n-3 fatty acids and the ratio of docosahexaenoic acid to arachidonic acid was associated with better cognitive function in late life before and after adjustment for childhood IQ.

Food supplement use and erythrocyte n-3 content are associated with better cognitive aging.
If associations with n-3 content are causal, optimization of n-3 and n-6 fatty acid intakes could improve retention of cognitive function in old age.