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Can eating fish reduce the risk of Alzheimer’s disease? Maybe it can.
(November 2004)

Oily fish (for example, mackerel, salmon) have a lot of omega-3 fatty acids. Eating these fish one or two times a week has been shown convincingly to reduce the risk of sudden death from severe abnormal heart rhythms during a heart attack or even in the absence of a heart attack. Other health benefits have been claimed for fish intake, most of them unproved. Now, there is some evidence that a good omega-3 fatty acid intake (from oily fish) can reduce the risk of Alzheimer’s Disease. At first, that might appear far fetched, but, in actuality, it might make sense. One of the omega-3 fatty acids in oily fish is DHA (docosahexaenoic acid). That fatty acid appears to be an important component of neurons in the brain. Several studies show that, in Alzheimer’s Disease, blood levels of omega-3 fatty acids are low, DHA in particular.

In several studies, cognition decline in older people or Alzheimer’s Disease have been associated with lower intake of fish; conversely, eating fish one or two times a week has offered considerable protection.

BUT,

- there are not yet enough studies

- in one of the small number of good studies, the 31 percent reduction in risk was not quite statistically significant

- in one widely quoted study published in 1997 (The Rotterdam Study), there was, based on a two-year followup, a clear reduction in risk of developing Alzheimer’s that appeared due to regular fish intake However, when the same group was followed longer, for six years, there was no relation at all to fish or omega-3 fatty acid intake.

Where does that leave us? It is plausible that omega-3 fatty acids are important in brain function and could protect against cognitive loss and Alzheimer’s in older people. That would be marvelous. Alzheimer’s is a terrible disease affecting about 10 percent of people over age 65 and more than one-third of those over age 85. There are now four million people in the United States afflicted with Alzheimer’s, and that number is expected to grow to 14 to 16 million by the year 2050. Eating oily fish one to two times a week may indeed reduce the risk of Alzheimer’s, but that is not yet adequately documented.

Eating oily fish once or twice a week is good for your heart and is part of a prudent diet. If it does help prevent Alzheimer’s, so much the better.

CLICK HERE for a list of fish with good content of omega-3 fatty acids.

There are two further questions:

1. Would fish oil supplements be just as good? The answer is probably yes, but no study on fish oil supplements on prevention of Alzheimer’s has been done so, at present, we do not know, and the evidence on protection from heart rhythm abnormalities by fish oil supplements is very limited. So, fish oil supplements may work, but we do not yet have enough evidence.

2. What about the plant sources of omega-3 fatty acids? (CLICK HERE for lists of plants with good content of omega-3 fatty acid in the form of alpha linolenic acid; flaxseed and flax and canola oils are the best sources). The plant sources (that is, the alpha linolenic acid) work as well as the fish omega-3 fatty acids in regard to protecting the heart against sudden severe abnormal and dangerous rhythms. Although a small amount of alpha linolenic fatty acid is converted in the body to DHA, we have no evidence that getting the omega-3 fatty acids from plants would be effective in reducing the risk of Alzheimer’s.

The Healthful Life recommendation is clear; include oily fish in your diet at least once a week (pregnant women should not eat any king mackerel or swordfish and limit tuna to no more than three-quarter pound a week because of concerns about mercury content).