By Judith Groch, MedPage Today Senior Writer Reviewed by Robert Jasmer, MD; Assistant Professor of Medicine, University of California, San Francisco April 18, 2006 Also covered by: BBC News MedPage Today Action Points
* When talking with patients, be aware that the Mediterranean diet, which showed a decreased Alzheimer's risk in this study, has also been linked to lower risks for cardiovascular disease, several forms of cancer, and overall mortality.
Review NEW YORK, April 18 - The Mediterranean diet may be brain food, according to a community-based study here.
A group of participants who stuck to elements of the Mediterranean diet -- high in fruits, vegetables, cereals, but low in meat and dairy products -- had a reduced risk for Alzheimer's disease. None was demented at the outset.
Overall, each additional unit of the Mediterranean diet adherence score (a zero to nine-point scale) was associated with a 9% to 10% decreased risk for Alzheimer's, reported Nikolaos Scarmeas, M.D., of Columbia University here, and colleagues, in the April issue of the Annals of Neurology and published online.
Compared with participants who had the lowest adherence to the diet, the risk for those with the highest adherence was 39% to 40% lower, while those in the middle tertile had a decreased Alzheimer's risk of 15% to 21%. This, the investigators said, showing a significant dose response, and sensitivity analysis did not change these findings.
This study suggested that "an overall dietary pattern is likely to have a greater effect on health than a single nutrient," Dr. Scarmeas said.
The Mediterranean diet is characterized by a high intake of vegetables, legumes, fruits, cereals; high intake of unsaturated fatty acids (mostly olive oil), but a low intake of saturated fatty acids; a moderately high intake of fish; a low to moderate intake of dairy products (mostly cheese or yogurt); a low intake of meat and poultry; and a regular but moderate intake of alcohol, primarily wine and with meals.
In the study, 2,258 non-demented community-based individuals from the Washington Heights-Inwood Columbia Aging Project were prospectively evaluated every 18 months for an average of four years. The primary outcome was the rate of decline in cognition as assessed at each study visit, using 12 neuropsychological tests and a semi-quantitative food questionnaire. During the course of the study, 262 individuals were diagnosed with Alzheimer's disease.
Adherence to the diet remained the main predictor even after adjustment for cohort, age, sex, ethnicity, education, apolipoprotein E genotype, caloric intake, smoking, medical comorbidity, and body mass index. Those adhering more to the diet tended to smoke less and had a lower calorie intake, the researchers said.
When individual components used to derive the Mediterranean pattern were examined in unadjusted Cox models, mild to moderate alcohol consumption, (0.61 [0.45-0.62] P=0.001) and higher vegetable intake (0.76 [0.60-0.97] P=0.30) were associated with decreased risk. Nevertheless, Dr. Scarmeas said, in adjusted models considering other confounders, none of the individual components was a significant predictor.
Previous research in Alzheimer's disease had focused on individual dietary components or nutrients, such as vitamins C and E, flavonoids, folate, total fats, and fish, often with conflicting results, the researchers said. There have been few studies of the effect of composite dietary patterns, rather than individual foods.
The results of this study, Dr. Scarmeas said, strengthen the researchers' initial hypothesis that composite dietary patterns can capture dimensions of nutrition that may be missed by individual components. Individuals do not consume foods or nutrients in isolation, but rather as components of their daily diet, he said.
The Mediterranean diet, which has been linked to a lower risk for cardiovascular disease, several forms of cancer, and overall mortality, may play a role in several potential mechanisms. These include oxidative stress and inflammation, both important in the pathogenesis of Alzheimer's, the investigators said.
Furthermore, they said, given the contribution of vascular risk factors to Alzheimer's disease, there is strong evidence linking the Mediterranean diet to lower vascular risks, such as hypertension, dyslipidemia, and diabetes. Vascular variables, the researchers said, are likely to be in the causal pathway between the diet and Alzheimer's.
The study had limitations, including possible inaccurate measurement of the patients' diets, though the researchers used previously tested assessments. There was also the possibility of disease misclassification, though experienced practitioners made the diagnoses. Subtle changes in dietary habits as a result of Alzheimer's symptoms were another potential limitation, although adherence was found to be stable. Finally, Dr. Scarmeas emphasized, the diagnosis of Alzheimer's took place in a university hospital with appropriate expertise in dementia.
This study examined the effect of the diet in a multiethnic community in the U.S. and the results support the notion that the diet's beneficial effects can be generalized to different populations, the researchers concluded.
Primary source: Annals of Neurology Source reference: Nikolaos Scarmeas, et al "Mediterranean Diet and Risk for Alzheimer's Disease," Annals of Neurology, 2006, 59, (6) and online April 18.
