Mediterranean Diet, Physical Activity Linked With Lower Risk Of Alzheimer Disease

Research regarding the effect physical activity can have on the risk of Alzheimer disease (AD) or dementia has shown mixed results, as has the effect of dietary habits. Their combined association has not been investigated, according to background information in the article.

Nikolaos Scarmeas, M.D., of Columbia University Medical Center, New York, and colleagues examined the association between physical activity and risk of AD and also the effect of physical activity and adherence to a Mediterranean-type diet on AD risk. The study included 2 groups that consisted of 1,880 community-dwelling elderly residents of New York city without dementia at the start of the study, for whom there was both diet and physical activity information available. Standardized neurological and neuropsychological measures were administered approximately every 1.5 years from 1992 through 2006.

The participants received measurements of their adherence to a Mediterranean-type diet (scale of 0-9; categorized as low, middle, or high) and their physical activity (sum of weekly participation in various physical activities, weighted by the type of physical activity [light, moderate, vigorous]; categorized into no physical activity, some, or much, also low or high), separately and combined. A higher score for diet was obtained with higher consumption of fruits, vegetables, legumes, cereals, and fish; lower consumption of meat and dairy products; a higher ratio of monounsaturated fats to saturated fats and mild to moderate alcohol consumption.

Individuals were followed up for an average of 5.4 years, during which a total of 282 developed AD. In considering only physical activity, the researchers found that more physical activity was associated with lower risk for developing AD. "Compared with physically inactive individuals, report of some physical activity was associated with a 29 percent to 41 percent lower risk of developing AD, while report of much physical activity was associated with a 37 percent to 50 percent lower risk," the authors write.

When considered simultaneously, both physical activity and Mediterranean diet adherence were significantly associated with AD incidence. According to the researchers, "Belonging to the middle diet adherence tertile was associated with a 2 percent to 14 percent risk reduction, while belonging to the highest diet adherence tertile was associated with a 32 percent to 40 percent reduced risk. Similarly, compared with individuals with no physical activity, individuals reporting some physical activity had a 25 percent to 38 percent lower risk for AD, while individuals reporting much physical activity had a 33 percent to 48 percent lower risk for AD."

The authors also write, "Compared with individuals with low physical activity plus low adherence to a diet (absolute AD risk, 19 percent), high physical activity plus high diet adherence was associated with a 35 percent to 44 percent relative risk reduction (absolute AD risk, 12 percent). … Absolute AD risks declined from 21 percent in the group with no physical activity plus low diet adherence to 9 percent in the group with much physical activity plus high diet adherence."

"In summary, our results support the potentially independent and important role of both physical activity and dietary habits in relation to AD risk. These findings should be further evaluated in other populations."

Higher Adherence to Mediterranean Diet Associated With Slower Cognitive Decline

In an examination of the association between adherence to a Mediterranean-type diet and cognitive performance and risk of dementia, researchers found that high adherence to the diet was associated with slower decline in some measures of cognitive function but was not associated with decreased risk for dementia, according to a study in the August 12 issue of JAMA.

Higher adherence to a Mediterranean-type diet is linked to lower risk for mortality and chronic diseases, and "might also have protective effects against cognitive decline in older individuals, because it combines several foods and nutrients potentially protective against cognitive dysfunction or dementia, such as fish, monounsaturated fatty acids, vitamins B12 and folate, antioxidants (vitamin E, carotenoids, flavonoids), and moderate amounts of alcohol," the authors write. But its association with cognitive decline has been unclear.

Catherine Féart, Ph.D., of the Université Victor Ségalen Bordeaux 2, Bordeaux, France, and colleagues examined whether adherence to a Mediterranean diet was associated with change in cognitive performance and with lower risk of all-cause dementia or Alzheimer disease. The study included 1,410 individuals (age 65 years or older) from Bordeaux, France, who were part of the Three-City cohort in 2001-2002 (a study of vascular risk factors of dementia) and were re-examined at least once over 5 years. Adherence to a Mediterranean diet (scored as 0 to 9) was computed from a food frequency questionnaire and 24-hour recall.

Cognitive performance was assessed on 4 neuropsychological tests: the Mini-Mental State Examination (MMSE), Isaacs Set Test (IST), Benton Visual Retention Test (BVRT), and Free and Cued Selective Reminding Test (FCSRT). New cases of dementia (n = 99) were validated by an independent expert committee of neurologists.

After adjusting for age, sex, education, marital status, energy intake, physical activity, depressive symptomatology, taking 5 medications/day or more, apolipoprotein E genotype, cardiovascular risk factors, and stroke, the researchers found that higher Mediterranean diet score was associated with fewer MMSE errors. But performance on the IST, BVRT, or FCSRT over time was not significantly associated with Mediterranean diet adherence, especially in those who remained free from dementia over 5 years. Mediterranean diet adherence was not associated with the risk for incident dementia, although the statistical strength of the data to detect a difference was limited.

"The Mediterranean diet pattern probably does not fully explain the better health of persons who adhere to it, but it may contribute directly. A Mediterranean diet also may indirectly constitute an indicator of a complex set of favorable social and lifestyle factors that contribute to better health. Further research is needed to allow the generalization of these results to other populations and to establish whether a Mediterranean diet slows cognitive decline or reduces incident dementia in addition to its cardiovascular benefits," the authors conclude.

Editorial: Mediterranean Diet and Late-Life Cognitive Impairment

In an accompanying editorial, David S. Knopman, M.D., of Mayo Clinic, Rochester, Minn., comments on the studies in this week's JAMA on diet, physical activity and risk of dementia and Alzheimer disease.

"A variety of approaches to mitigating cerebrovascular disease in midlife exist, including diet, exercise, treatment of hypertension, treatment of diabetes, avoidance of obesity, and avoidance of smoking. The findings of Scarmeas et al and Féart et al fit into a larger and potentially optimistic view of prevention of late-life cognitive impairment through application, at least by midlife, of as many healthy behaviors as possible, including diet. Based on these 2 studies, diet may play a supporting role, but following a healthy diet does not occur in isolation."

"The scientific value of these studies cannot be disputed, but whether and how they can or should be translated into recommendations for the public is the question."