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EAT OILY FISH ONCE A WEEK AND REDUCE YOUR RISK OF ALZHEIMER’S BY 60 PERCENT. MAYBE.
(January 2004)

There is a huge amount of interest in the possibility of preventing Alzheimer’s disease through dietary approaches. It is said that saturated fats, overweight, trans-fatty acids all increase risk, whereas unsaturated fats are protective, but all of these factors are inadequately documented. To the potential protective factors add oily fish with their high content of omega 3 fatty acids. The investigators followed 813 persons, ages 65 to 94. Over a four-year followup period, 131 developed Alzheimer’s disease. The participants were divided into five groups (quintiles) from lowest to highest consumption of fish and omega 3 fatty acids. The main findings were as follows:

- Eating fish (type unspecified) one to three times a month reduced risk of Alzheimer’s by 40 percent. Eating fish weekly reduced risk by 60 percent with no additional benefit from eating fish two or more times a week.

- Total omega 3 fatty acids (found especially in oily fish) reduced risk by 60 percent in the highest intake group.

- The top three quintiles in the intake of a critical omega 3 fatty acid, docosahexaenoic acid, showed a 60 to 80 percent reduction in risk.

- Increasing consumption of alpha linolenic acid, an omega 3 fatty acid found in certain salad oils (particularly flax seed and canola oils), nuts, and some vegetables, showed no overall reduction in risk, but a significant reduction in a subgroup who had a certain genetic make up.

The authors concluded “our findings suggest that consumption of fish at least once weekly, oil-based salad dressings, and nuts may reduce risk of Alzheimer’s disease”.

Commentary: This is an interesting study, but there are some problems:

- There was only one question asked on the baseline questionnaire about fish consumption as a main dish. The type of fish and portion size were not determined. That makes any conclusion about an individual’s omega 3 fatty acid consumption somewhat uncertain.

- When the 131 cases are divided into five groups (quintiles) by fish or omega 3 fatty acids intake, the numbers in each group are small (about 25). That makes it critical to be cautious in regard to making dogmatic conclusions.

There is an additional problem. The authors quote two supporting studies. One of the two, the Rotterdam Study, did indeed show that good fish intake reduced risk of developing Alzheimer’s, but that was with a two-year followup. When the same group was followed for a longer period, six years, total fat, omega 3 fatty acid, and fish intake made no difference at all in Alzheimer risk. So, one of the two “supportive” studies was, in point of fact, a contradictory study.




At present, there is no persuasive evidence indicating eating oily fish protects against Alzheimer's, but eating oily fish once or twice a week does help reduce risk of heart attack and death from severe abnormal heart rhythms (CLICK HERE for a list of oily fish; CLICK HERE for a list of plant sources of omega 3 fatty acids) and should be part of a prudent, healthy diet.

Morris, M.G., et al. Fish consumption and the risk of Alzheimer Disease. Archives of Neurology. Vol 60 (July) Pgs 940-946. 2003.

New studies on the topic are being published. We will revisit the possible protective action of fish and omega-3 fatty acids against Alzheimer’s about six months from now.