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Omega-3 fatty acids in the prevention of Alzheimer’s - more encouraging evidence
(March 2007)

There are now multiple studies suggesting that eating oily fish that provides good amounts of omega-3 fatty acids can significantly reduce the mental function and thinking loss that accompanies the aging process and lower the risk of Alzheimer’s Disease.  However, there are inconsistencies in the data and uncertainties about the amount of oily fish intake required.  More supportive data comes from the renowned Framingham Heart Study.  They enrolled 899 men and women, average age about 76 years, and followed them for an average of nine years.  At enrollment, blood was obtained for fatty acid determination, in particular for the omega-3 fatty acid, docosahexaenoic acid (DHA).  DHA is found in considerable content in the brain and appears to be critical for brain development and function.  Blood DHA levels were divided into four groups (quartiles) and the highest DHA quartile was compared with the three lower quartiles.  The likelihood of developing dementia specifically of the Alzheimer's type in the top DHA quartile.  The risk of developing dementia, specifically of the Alzheimer’s type, in the top DHA quartile was reduced by 38 percent, but that reduction was not statistically significant.  The top DHA blood level quartile that reduced dementia risk correlated with a fish intake of three servings per week.  Of note, there was no evidence that the other major omega-3 fatty acid in oily fish, eicosapentaenoic acid (EPA), provided any protection against dementia.

Commentary: This is an interesting study and it does add some new encouraging data.  But, it is hardly definitive.  The following are the major issues.

- The blood DHA level was measured only once, at enrollment.

- Most of the findings of a reduced dementia or Alzheimer’s risk were not statistically significant.

- The reduced risk in the top DHA quartile did not take into account (adjust for) either dietary patterns or physical activity in dementia patients and controls.  Potentially, on the basis of other studies, either greater physical activity or a Mediterranean type diet could have produced the reduced risk of dementia, rather than DHA levels or fish intake.

Additionally, the type of fish in the diet was not analyzed.  Three servings of fish a week appeared to be somewhat protective, but it is not clear how many of those servings were oily fish.  It seems quite likely that the high DHA quartile would be achieved by eating oily fish twice a week (CLICK HERE for a table of fish with good content of omega-3 fatty acids).  Indeed, an average portion of mackerel once a week would seem to provide enough DHA to attain the highest quartile and that may also be true for salmon.  A previously reviewed study (see Archives under Alzheimer’s “Eat oily fish once a week and reduce your risk of Alzheimer’s by 60 percent”) found that one serving a week of oily fish reduced Alzheimer risk by 60 percent.

Schaefer, E.J., et al.  Plasma phosphatidylcholine docosahexaenoic acid content and risk of dementia and Alzheimer Disease.  Archives of Neurology.  Vol 63 (November) Pgs 1545-1550.  2006.

More studies are needed, but this is encouraging.  There is a very good argument for obtaining adequate omega-3 fatty acids in your diet; it will be good for your heart and perhaps for your mind.  Oily fish (but not lean fish) once or, better still, twice a week (depending on which type of oily fish you choose) will provide the needed amount of the omega-3 fatty acids.  DHA can also be obtained from plant sources high in alpha linolenic acid which is converted in the body to DHA (CLICK HERE for a list of plants high in alpha linolenic acid).  However, plant alpha linolenic acid is readily converted to EPA, but provides much less DHA, and it is not certain that enough DHA will be produced to affect mental function.  Supplements containing omega-3 fatty acids probably are effective for the heart, but, thus far, there are few studies; consequently, their effectiveness is presumed, not documented.  There are virtually no studies on the effectiveness of omega-3 supplements on brain function.