When I was young I was told that eating fish made you clever, in the same way that eating carrots made you see in the dark. Luckily I always liked fish, though whether it had the desired effect upon my intellect it is not for me to say.
At any rate, the connection between eating fish and brain function has long been part of common folklore, and it is probably for this reason that large numbers of people approaching old age take fish oil capsules in the hope of warding off Alzheimer’s disease. This, no doubt, is an example of the belief or superstition that, if only we got our diet right, we should never fall ill. Immortality is but a diet away.
A meta-analysis of trials of fish oil capsules or margarine in the prevention of cognitive decline has just been published in, or on, the Cochrane Library, a website devoted to examining the evidence for (or of course against) the use of drugs and medical procedures in the prevention and treatment of illnesses. The quality of the analyses published in, or on, the Cochrane Library is generally accepted as the best possible.
The authors aggregated the results of three trials that met their methodological criteria. The trials had to be double-blind and placebo-controlled, and involved 3,536 participants who were cognitively unimpaired and over the age of 60. Subjects took fish oil capsules or margarine (or placebo) for 6, 20 or 40 months.
There was no evidence that fish oils prevented cognitive decline as measured by the Mini-Mental State Examination, the measuring instrument usually used in such trials, and other simple tests. The only significant side-effect of taking fish oil was mild gastrointestinal disturbance; overall levels of side-effects were as great among those taking placebo as those taking fish-oil.