Americans who ate a
Mediterranean diet - lots of
fruits, vegetables, legumes, cereals, some
fish and alcohol, and little dairy and meat
- had a reduced risk for Alzheimer's disease
as they aged. These findings are published
in the April issue of Annals of Neurology, a
journal published by John Wiley & Sons. The
article is also available online via Wiley
Interscience (interscience.wiley.com).
Experts theorize that diet
may play a role in the development of Alzheimer's
disease but epidemiological data on diet and Alzheimer's
is conflicting and while individual foods and nutrients
have been previously studied, general dietary patterns
have not. To address this paucity of data, researchers
led by Nikolaos Scarmeas of Columbia University Medical
Center, designed a prospective community-based study of
2,258 non-demented people in New York City. The study
was funded by the NIH/NIA.
The subjects were part of
the
Washington Heights-Inwood
Columbia Aging project, and for each,
the researchers gathered medical and neurological
history, did a standardized physical and neurological
exam, and conducted an in-person interview to assess
health and neuropsychological function. This information
was used to diagnose a presence or absence of dementia.
Subjects were reassessed approximately every 18 months
for an average of 4 years.
The researchers also
obtained dietary data from each subject using a
semi-quantitative food frequency questionnaire. They
determined a Mediterranean Diet score
(0-9) based on a previously described method. During the
course of the study, 262 members of the study population
were diagnosed with Alzheimer's disease.
"Higher adherence to the
Mediterranean diet
was associated with significantly
lower risk of
developing Alzheimer's disease," the
authors report. For each additional point to
Mediterranean diet scores (indicating increased
adherence to the diet), Alzheimer's risk dropped by 9 to
10 percent. Compared with the subjects in the least
adherent group that adhered to a Mediterranean diet the
least, subjects in the middle tertile had 15 to 21
percent lower risk of developing Alzheimer's disease,
and those in the highest tertile had a 39 to 40 percent
lower risk, suggesting a significant dose response
effect. The association remained significant even after
adjusting for potential confounders such as age, gender,
ethnicity, education, caloric intake, BMI, smoking and
comorbid conditions.
One possible limitation
of this study is the inaccurate measurement of subjects'
diets, though the researchers used a previously
developed and tested dietary assessment, and suggest
that mismeasurements may have actually caused an
underestimation of the association. Also, disease
misclassification is a possible limitation, though the
diagnosis was made by experienced practitioners and was
based on comprehensive assessment and standard criteria.
Subtle changes in dietary habits as a result of early
Alzheimer's symptoms, although another potential
limitation, did not seem to be the case since adherence
to the Mediterranean diet was found to be quite stable.
"We conclude that higher
adherence to the
Mediterranean diet
is associated with a reduction in risk for Alzheimer's
disease," they say. In addition, they say that the
beneficial effects of the Mediterranean diet for
non-neurological conditions have been previously shown
to be generalizable to different populations, and that
the current study provided the opportunity to examine
the effect of this diet for a neurological disease in a
multiethnic community in the U.S.
