Fish Really Is Brain Food!

Summarized by Robert W. Griffith, MD
November 7, 2005

Introduction

Mother knows best - she told you that the fish you eat makes brains, and it looks as if she was right. Previous studies have shown that eating fish is associated with a decreased likelihood of dementia and stroke. It's been assumed this is due to the omega-3 content of fish. Now researchers from the Rush Institute for Healthy Aging have published results of a study if the possible protective effect of eating fish on the age-related 'cognitive decline' ¹ that occurs in just about everyone.

This study has been published in the Archives of Neurology; we provide a summary of the findings here.

What was done

Participants in the Chicago Health and Aging Project (CHAP) volunteered for this study. There were 6,100-plus residents 65 years of age and older - 62% black and 38% white. Baseline testing of mental functioning was done between 1993 and 1997, and repeated in two follow-ups every three years. There were 4 standardized tests: immediate and delayed recall, the Mini-Mental State Exam (often used to help diagnose Alzheimer's), and the Symbol Digit Modalities Test (an early screen for cerebral dysfunction, or disturbed mental functioning).

The participants completed a food-frequency questionnaire once, about 15 months after their baseline assessment. Four seafood items were included in the questions. Weekly fish consumption was estimated from the responses.

It was planned to calculate changes in the total cognitive scores over the study period, and compare these with the fish intake levels.

What was found

Fish consumption was low to moderate, with one in five participants eating 2 or more fish meals a week. About two in five ate fish less than once a week. The cognitive scores showed a decline from an average of 0.18 units at baseline at a rate of 0.04 units per year.

Those people who ate fish at least twice a week reduced their rate of decline by 13%, compared with those who rarely or never ate fish. If they ate fish 1 to 2 times a week, their decline was 10% less than that of the rare- or never-eaters. These calculations were made after adjusting for age, gender, race, educational level, mental and physical activities, alcohol use, and total calorie intake.

There was no evidence that people who ate more fish had important differences in their intake of fruit or vegetables, or that they had any cardiovascular conditions. However, the group who ate fish twice a week or more had a slightly increased intake of unsaturated fats, and a decreased intake of saturated and trans fats, compared with the others.

Analyses showed that the intake of total omega-3 fatty acids (long thought to be relevant for most of the benefits provided by eating fish) didn't affect the rate of cognitive decline in these subjects.

What this means

The conclusions to be drawn are fairly simple. Eat more fish! But is this safe? Recently, the mercury content of fish has caused concern, and there's a risk that people may shun this excellent source of nourishment. Researchers at the Harvard Center for Risk Analysis have weighed the evidence for and against eating fish, and find that the mercury risk is only relevant for pregnant women. Eating too much mercury-containing fish in pregnancy can harm the unborn child. But not eating enough fish, for the rest of us, means we lose the demonstrated benefits on the cardiovascular and cognitive systems.

Doubtless efforts will be made to reduce the mercury content of fish. In the meantime, pregnant women (or those who might become pregnant) should avoid eating shark, swordfish, king mackerel, and tile fish, which are known to have lots of mercury. The rest of us should go ahead, and eat more fish!

Source

• Morris MC, Evans DA, Tangney CC, et al. Fish consumption and cognitive decline with age in a large community study. Arch Neurol 2005;62:1-5 Cohen JT, Bellinger DC, Connor WC, Shawitz BA. A quantitative risk-benefit analysis of changes in population fis

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