I stared at the the man.A century ago, the evidence that fish is brain food was virtually nonexistent. Researchers have been looking at this question ever since, and the evidence has been mixed. Even if fish is good for the brain, the mercury content in some fish might have the opposite effect.
'How many tins of sardines did you eat, Jeeves?'
'None, sir. I am not fond of sardines.'
'You mean, you thought of this great, this ripe, this amazing scheme entirely without the impetus given to the brain by fish?'
'Yes, sir.' [From Very Good, Jeeves, (c) 1930 by P.G. Wodehouse]
A new study that appeared last week in JAMA answers this question: fish is indeed good for the brain. More precisely, eating fish regularly was associated with a reduced risk of Alzheimer's disease. This benefit occurred despite the fact that people who ate more fish did have higher levels of mercury in the brain. Apparently, the levels of mercury were too low to cause harm, and the benefits of eating fish easily outweighed any risks.
The new study, by Martha Clare Morris and colleagues at Rush Medical Center in Chicago, looked at 554 Chicago residents, all part of a long-term aging study, who died over a ten-year period. The scientists conducted autopsies to look directly in the brain for physiological changes such as neuritic plaques, which are signs of Alzheimer's or other disease. They used questionnaire data, which they collected for everyone in the study, to measure how much fish people had been eating–an imperfect way to measure eating habits, but it's often the only realistic way to gather this information.
Here's what they found: people who ate seafood at least once per week had lower levels of three different physiological signs of Alzheimer's, but only in people with a genetic marker known as APOE ε4, which itself carries an increased risk of Alzheimer's. (None of the people in the study had dementia when they first enrolled, starting in 1997.) Somehow, then, eating fish seems to counteract the effects of this harmful genetic mutation.
Bad news for fish oil supplement makers: the study found that "fish oil supplementation had no statistically significant correlation with any neuropathologic marker." In other words, people who took supplements got no benefit. You just have to eat fish.
This isn't the first study to show a positive benefit to brain health from eating fish. The authors cite 13 previous studies that reported "protective relations between seafood consumption and n-3 fatty acids with cognitive decline and incident dementia." The JAMA study is the first to include mercury levels, brain changes associated with Alzheimer's, and diet all in the same study. It's reassuring to learn that despite the increased mercury caused (probably) by eating more fish, the overall effect is beneficial.
The authors also pointed out that as we age, our brains lose DHA, a critical lipid in the brain, and that therefore "fish consumption may be more beneficial with older age." The FDA already recommends that pregnant women and young children eat more fish for its nutritional benefits. Now there's evidence that older people should eat fish regularly too.
So it seems that Wodehouse's character Bertie Wooster might have been right: fish really is brain food.