ARTICLE IN BRIEF
Investigators reported in one study that people who followed a Mediterranean-type diet and who were also physically active had a 60 percent lower risk for AD during a 5.5-year period. In another study, the diet did not seem to lower the risk for progression to AD.
Older people who consume a diet high in fruits, vegetables, legumes, cereal, and fish — the Mediterranean way of eating — and who are physically active have a reduced risk for Alzheimer disease (AD), according to an analysis of results from the longitudinal Northern Manhattan study of 1,880 elderly people living in that New York city neighborhood.
Both the Mediterranean diet and moderate exercise have an independent benefit, said Nikolaos Scarmeas, MD, assistant professor of neurology at the Columbia University Taub Institute Division of Aging and Dementia and lead author of the study published in the August 12 JAMA.
Dr. Scarmeas and colleagues have been monitoring the physical and cognitive health — collecting lifestyle, health, and disease information — from 1,880 people from Northern Manhattan every 18 months since 1992. At the study onset, the average age was 77 years and participants were cognitively fit with no symptoms of dementia and within normal range on neuropsychological testing. The epidemiological study was designed to track how lifestyle and environmental factors factor into a subsequent diagnosis of AD.
Since 2006, the investigators have reported that the Mediterranean diet reduced the risk for mild cognitive impairment and AD. The Mediterranean diet combines several foods and nutrients such as fish oil, monounsaturated fatty acids, vitamins B12 and folate, antioxidants (vitamin E, carotenoids, flavonoids), and moderate amounts of alcohol.
This latest study adds physical activity to the mix in an attempt to show independent protective factors.
STUDY PROTOCOLS, RESULTS
The researchers obtained information about dietary and exercise habits at the initial visit and then looked back to determine if these lifestyle factors had any impact on the 282 individuals who developed AD five and a half years later.
As a prospective study, they created many different groups based on their dietary and exercise habits over the time period studied. They included people who had a poor diet — high in meat and dairy and low in fruits, vegetables, legumes, cereal, olive oil, and fish — and who did not exercise at all and those who ate diets rich in Mediterranean fare and who spent on average approximately four hours a week on light exercises (or 2.5 hours on moderate or 1.5 hours on vigorous activity). Then they broke it down into eaters who consumed small and moderate amounts of a food consistent with a Mediterranean diet and those who spent modest time exercising.
Those who reported following a Mediterranean-type diet and who were also physically active had a 60 percent lower risk for AD during a 5.5-year period. Twenty-one percent of those who had a poor diet and were physically inactive developed AD over a 5.5-year period compared to 9 percent of those who followed a Mediterranean-type diet and reported good exercise habits.
Individuals who said that they were moderately physically active, rated with a weekly activity scale, had a 25- to 38-percent lower risk of developing AD than those who were physically inactive.
The independent benefits of diet and exercise were still present when they adjusted for age, gender, ethnicity, genetic risk factors (for example, the apolipoprotein genotype), caloric intake, body mass index, other diseases, smoking, depression, and cognitive and social activities.
DIFFERENT FINDINGS: FRENCH STUDY
In the same issue of JAMA, a team of French scientists looked at the benefits of the Mediterranean diet in 1,420 people over 65 living in Bordeaux who were part of a larger three-city study to identify risk factors of dementia. The scientists, led by Catherine Féart, PhD, of the Universite Victor Segalen, used a food frequency questionnaire to measure a person's food choices.
The people in France were given a battery of four neuropsychological tests. At the end of five years, the scientists compared adherence to a diet rich in plant foods and olive oil, a healthy source of monounsaturated fats, against changes in the neuropsychological tests taken during the study. Those who kept to a Mediterranean diet had higher Mini-Mental State Examination scores over five years than those who chose the fattier foods that are common in a Western diet. Their dietary choices had no effect on the other three neuropsychological tests.
During the five-year period, 99 people developed AD. Their diet did not seem to affect the development of the AD, contrary to a 2006 report from the Columbia group, led by Dr. Scarmeas. The scientists said their study did not include enough AD patients to enable them to adequately study the effects of diet and exercise.
“The Mediterranean diet pattern probably does not fully explain the better health of persons who adhere to it, but it may contribute directly,” Dr. Féart and her colleagues wrote. “A Mediterranean diet may indirectly constitute an indicator of a complex set of favorable social and lifestyle factors that contribute to better health.”
APPLICATIONS FOR PRACTICE?
“These results are interesting but they need to be looked at cautiously,” said David S. Knopman, MD, professor of neurology and an Alzheimer disease researcher at the Mayo Clinic in Rochester, MN, who wrote an accompanying editorial in the same issue of JAMA. “The scientific value of the studies cannot be disputed, but whether and how they can or should be translated into recommendations for the public is the question.”
Dr. Knopman said that there are many possible alternative explanations for these results. For example, it could be that it is not just the diet or the exercise per se but a “healthy person effect.” People who eat a healthy diet and exercise may have other characteristics that help to lower their risk for all sorts of illnesses. “Therefore,” said Dr. Knopman, “to make sweeping public health recommendations about changes in diet such as avoiding meat, for example, or encouraging olive oil, have huge financial, economic, social, and political implications. The certainty of the results of the Scarmeas and Féart studies is sufficiently low that it would be premature to recommend dietary changes to the public at large.”
Dr. Scarmeas agrees that more and different type of studies should be conducted to confirm these results. Still, he said: “It may well be worth doing both. Each adds something unique.”
As a neurologist, he recommends a healthy diet and exercise because of its known health benefits for many non-neurological conditions, including cardiovascular disease and certain cancers.
No one knows why a Mediterranean diet would potentially protect the brain from dementia or slow cognitive decline. Walter Willett, PhD, chairman of the department of nutrition at Harvard School of Public Health, said that many of the diet risk factors that protect the heart are also emerging as protection for the brain. “There is strong evidence that Alzheimer disease is related to vascular disease,” said Dr. Willett, co-author with food writer Mollie Katzen of Eat, Drink and Weigh Less: The Harvard Medical School Guide to Healthy Eating (Hyperion). “The types of fats that we eat, and the wine we drink, could benefit our health.”