A new study, from the Rush-Presbyterian, St. Lukes Medical Center, in Chicago, shows that people who consumed at least one serving of fish a week dramatically reduced their risk of Alzheimer’s disease, compared to those who rarely or never ate fish. Dietary intake of omega-3 fatty acids had a similar risk-lowering effect.1
The prospective study involved 815 Chicago nursing home residents, aged 65 to 94, unaffected by Alzheimer’s disease (AD). Participants completed a dietary frequency questionnaire that included 4 seafood items: Tuna fish sandwich, fish sticks/fish cakes/fish sandwich, fresh fish as a main dish, and shrimp/crab/lobster. Total omega-3 fatty acid (n-3) intake was calculated as the sum of alpha linolenic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).2
After an average follow up of 3.9 years, 131 of the participants were diagnosed as having AD. The incidence of AD was inversely associated with fish consumption. Persons who ate fish once a week or more shaved a 60% lower risk of AD, compared to those who rarely or never ate fish (fresh fish as the main course was the type consumed most frequently). A similar inverse association was found with total n-3 fatty acid intake. Persons who consumed the highest amounts (median 1.75 g/day), had a 70% reduced likelihood of having AD, compared to those with the lowest intake (median 0.9 g/day).3
Of the marine fatty acids (EPA, DHA) only DHA was protective, reducing the risk of AD by 60%, in age- adjusted calculations. DHA is the most abundant fatty acid in brain phospholipids, present in high amounts in the cerebral cortex, mitochondria, and neural connections. EPA had little effect on AD risk, as intake was low, with 40% of participants consuming 0 g/day. (In a 24 hour dietary recall, more than 90% of 234 participants said they ate fish low in fat.) Dr. Martha Claire Morris, the lead investigator, conceded that one cannot rule out a protective effect of EPA, obtained by intake of fatty fish or fish oil supplements. Intake of linolenic acid (found mainly in vegetable oil-based salad dressing and nuts) was protective in persons carrying a gene that has been linked to risk of AD.
The study adds to previous findings on the relationship between fish consumption, n-3 fatty acids and brain health. A Canadian study showed that n-3 fatty acid levels in plasma phospholipids of patients with AD and other cognitive disorders were lower compared to levels in age-matched controls; a large study in France, of people aged 68 and older, showed that “elderly people who eat fish at least once a week are at a lower risk of developing dementia, including AD.” The authors suggested that “in addition to providing vascular protection, the fatty acids contained in fish oils could reduce inflammation in the brain.”
An accompanying editorial to the Chicago report, suggested that a healthy diet containing antioxidant-rich foods and fish is likely to lower the risk of AD and other ailments, and that fish oil supplements can be good sources of omega-3 fatty acids.
—Carmia Borek, Ph.D.