24 April 2006. For those of us tinkering with diet to achieve better health and stave off Alzheimer disease, new research in the April Annals of Neurology provides a possible recipe for success—namely, the Mediterranean diet. The diet—lots of fruits, vegetables, legumes and grains, favoring fish over red meat, cooked with olive oil and consumed with a moderate amount of wine—has been previously shown to reduce the risk of heart disease, and the new study shows a dose-dependent decrease in risk for AD with increasing adherence to the diet.
The study, from Nikolaos Scarmeas, Richard Mayeux, Jose Luchsinger and colleagues at Columbia University in New York City, provides important new data on the effects of a composite dietary pattern on brain health. Such studies may help bring clarity to the conflicting data from analyses focusing on one or two nutrients or supplements rather than the full dietary context.
Among the lifestyle factors that affect AD, diet ranks among the top. A wealth of epidemiological data and animal models shows that what we eat, and even what we don’t eat—think calorie restriction—can influence the risk of developing AD (see ARF related Live Discussion and ARF Forum Discussion). But the epidemiological data on the role of particular dietary components or additions, for example, antioxidants like Vitamin E and C, and omega-3 fats, are inconsistent. As the Mediterranean diet is rich in nutrients suspected of preventing AD, and low in trouble-causing cholesterol and saturated fats, Scarmeas and colleagues hypothesized that higher adherence to the diet as a whole would lower the risk of AD. By studying an eating pattern, rather than a single component, they hoped to find effects that might be attributed to dietary complexity and interactions among nutrients.
The study, part of their ongoing, community-based aging project, tracked 2,258 nondemented people in New York City for an average of 4 years, with some followed up to 13 years. For each subject, the researchers took a medical and neurological history, did a standardized physical and neurological exam, and conducted an in-person interview to assess health and neuropsychological function. The researchers also obtained dietary data at the first visit, and determined a Mediterranean Diet (MeDi) score from 0 to 9 by comparing consumption of fruits, vegetables, dairy, meat, legumes, cereals, fish, fats, and ethanol to previously defined levels. They then compared the score with cognitive decline as measured at successive follow-ups. Subjects were reassessed approximately every 18 months, resulting in 262 new diagnoses of AD over the course of the study.
Higher adherence to the Mediterranean diet was associated with a lower risk of AD across MeDi scores, although the effect was modest (hazard ratio 0.91, with a 95 percent confidence interval of 0.83-0.98). But separating out the highest and lowest adherence tertiles revealed a dose-response effect, with the most reduction in risk among people with the highest MeDi scores. Compared with subjects in the lowest tertile (MeDi scores of 0-3), subjects in the highest tertile (scores of 6-9) had a 40 percent lower risk, while subjects in the middle tertile (scores of 4-5) had 15-21 percent less risk of AD. The authors also observed a significant interaction between higher adherence to MeDi and a slower rate of cognitive decline. The risk reduction remained similar and statistically significant after adjustment for common confounding factors of age, sex, ethnicity, education, apolipoprotein E4 status, caloric intake, and body mass index. (Luchsinger and Mayeux’s previous study in the same demographic showed a higher risk of AD with higher caloric intake; (see ARF related news story).
“We conclude that higher adherence to the Mediterranean diet is associated with a reduction in risk for Alzheimer’s disease,” the authors write. Interestingly, none of the nine individual components that made up the MeDi score was associated with reduced risk for AD in adjusted models. “These results strengthen even further our initial hypothesis that composite dietary patterns can capture dimensions of nutrition that may be missed by individual components, and that an overall dietary pattern is likely to have a greater effect on health than a single nutrient,” they conclude.
The potential to draw inaccurate conclusions in dietary studies is large, based on the difficulty in accurately measuring diet, the veracity of clinical diagnoses, and the presence of numerous confounding variables. Keeping the caveats in mind, the study is consistent with previous work showing that health benefits of similar diets on cardiovascular disease and cancer. Studies have shown that the Mediterranean diet, much lower in saturated fat than the American diet, is associated with lower inflammatory markers. Thus, eating the Greek way reduces oxidative stress and inflammatory damage, both implicated in the pathogenesis of AD. The diet’s effects could also be due to its benefits to the vascular system, since vascular risk factors contribute to the risk of AD. Whatever the reason, the results suggest that the health effects of the Mediterranean diet go beyond the heart, and that the benefits translate well to multi-ethnic populations, in this case a group of Manhattanites. On that note, please pass the olives (and vino).—Pat McCaffrey.
Scarmeas N, Stern Y, Tang MX, Mayeux R, Luchsinger JA. Mediterranean diet and risk for Alzheimer's disease.
Ann Neurol. 2006 Apr 18; [Epub ahead of print]