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Can the Mediterranean diet help prevent Alzheimer’s?
(June 2007)

Healthful Life has been very skeptical about the myriad of articles on preventing Alzheimer’s with various diets, vitamins, physical exercise, and mental exercise.  We have also been skeptical of a preliminary study from Columbia University Medical Center about the ability of the “Mediterranean diet” to reduced the risk of Alzheimer’s in a group of older New York City residents (see Archives under “Alzheimers”, ‘Can the Mediterranean diet prevent Alzheimers?’).  Now, the same group has studied two other New York City groups, average age about 76 years, comparing the diet in 1,790 persons without dementia and 194 with relatively early stage Alzheimer’s.  The investigators made up a “Mediterranean diet” score for each individual and then divided those without Alzheimer’s and those with Alzheimer’s into three categories - low, medium, and high adherence to the “Mediterranean diet”.  The diet score was created by giving positive points for a good intake of vegetables, fruits, legumes (peas, beans), cereals, fish, and for moderate use of alcohol.  Negative points were given for good intake of dairy products and meat.  Those in the middle “Mediterranean diet” scores had about a 50 percent reduced risk of Alzheimer’s; those in the highest “Mediterranean diet” intake had almost a 70 percent reduced risk.

Alzheimer’s may be related, in part, to vascular variables such as high blood pressure, elevated cholesterol and low-density lipoprotein cholesterol (LDL, bad cholesterol) levels or to diabetes.  The investigators then adjusted for these variables, but that did not change the results, suggesting that the diet did not act by lowering blood pressure, cholesterol, or LDL levels.

Commentary: This seems to be an impressive report.  It does look as if the diet may have reduced risk of Alzheimer’s.  But, there are two issues.

First, this is not a Mediterranean population and it is not strictly a Mediterranean diet.  That diet is also high in fruits, vegetables, fish, legumes, cereals, and breads, but critical components are olive oil, wine, and nuts and seeds which are not apparently a significant part of the diets of this study group.  Furthermore, the Mediterranean diet is low in red meat and eggs, but it includes moderate amounts of poultry and dairy products.  It is not clear why negative points would be given for being in the upper half of dairy product intake.  The dietary score does reflect a prudent diet, but it is not really a Mediterranean diet score.

Second, it is a crude dietary measurement; each food category was given a rating of 0 or 1.  That is hardly a good quantitative measurement.  And, we need much more information about the type of vegetables and type of fish.

Additionally, this study started with Alzheimer cases and compared them to controls.  That type of study is less likely to be confirmed than studies that place people on a specific diet and then follow them, together with controls, for subsequent development of dementia.

If the diet did reduce risk of Alzheimer’s as is suggested by the dose-response (greater reduction in risk as adherence to the diet increases), reduction in blood pressure or lowering cholesterol or LDL levels does not appear to be the mechanism.  The authors suggest it may be due to antioxidant or anti-inflammatory effects of the diet.  A recent article shows reasonably persuasively that the Mediterranean diet does lower blood pressure, cholesterol levels, and blood sugar levels (see Archives under “Diet”, ‘More evidence on the Mediterranean diet - and it’s pretty positive’).  This emphasizes that this should be called a prudent diet score, not a Mediterranean diet score.

Interesting, but it is not really a true Mediterranean diet and the dietary score is too crude.  If the diet is effective, there is no hint as to which components(s) of the diet is (are) responsible for the benefit.  Other studies would suggest that it might be omega-3 fatty acids in oily fish in the diet - but, in this study, we are not told whether the fish consumed were high in omega-3 fatty acid content.

More studies are needed, but this and other recent studies do offer hope that certain dietary patterns will be found that reduce the memory impairment that often accompanies aging and might even reduce the risk of Alzheimer’s – and, of course, adhering to the prudent diet is a good idea and is good for your health.

Scarmeas, N., et al.  Mediterranean diet, Alzheimer Disease and vascular mediation.  Archives of Neurology.  Vol 63 (December)  Pgs 1709-1717.  2006.