ARTICLE IN BRIEF
- ✓ Compared with those with the lowest adherence to the Mediterranean diet, participants with moderate adherence were up to 35 percent less likely to die, while those with the highest adherence to the diet were up to 73 percent less likely to die.
A Mediterranean-style diet may not only protect against Alzheimer disease (AD), but may also help patients who have the disease live longer, according to a new study published in the Sept. 11 Neurology (69:1084–1093).
The study tracked the diets of 192 elderly residents of northern Manhattan who had been diagnosed with early Alzheimer disease. The subjects who followed a Mediterranean-style diet most closely lived an average of 3.9 years longer than subjects who adhered to the diet the least.
The Mediterranean diet is characterized by high intake of vegetables, legumes, fruits, cereals, fish, and unsaturated fats such as olive oil, along with a low intake of meat and poultry, a moderate intake of dairy products, and regular but moderate amounts of ethanol, typically wine with meals.
The study was led by Nikolaos Scarmeas, MD, assistant professor of neurology at Columbia University Medical Center.
Investigators visited participants in their homes every 18 months for an average of 4.4 years. They were examined neurologically, given neuropsychological tests to determine progression of dementia, and questioned about their dietary habits. Participants' diets were ranked 0–9, with higher scores indicating higher adherence to the Mediterranean diet.
Compared with those with the lowest adherence to the diet, participants with moderate adherence were up to 35 percent less likely to die, while those with the highest adherence to the diet were up to 73 percent less likely to die. The data suggest a possible dose-response effect. “This study indicates that the more you adhere to the diet, the bigger the benefit will be,” said Dr. Scarmeas.
The study comes on the heels of a 2006 study led by Dr. Scarmeas, which found that people who followed a Mediterranean diet were up to 40 percent less likely to develop AD than people who did not (Ann Neurol 2006;67:998–1005).
The new research lets AD patients and their families know that “there are things they can do to help even after Alzheimer disease has started,” Dr. Scarmeas said. “There is a point to being careful about diet because we may be able to affect the duration of the time we live.”
Dr. Scarmeas said the study addressed the possibility that AD patients may have trouble recollecting their diet by querying family members and caretakers about what the participants ate. The study also included only subjects with early-stage Alzheimer disease. “Their cognitive function was impaired, but not very impaired,” he said. The study also adjusted for cognitive performance. Researchers performed additional analysis on a separate group of subjects who reported dietary information before being diagnosed with AD. “Even with those people, higher adherence to the diet related to improved survival,” Dr. Scarmeas said.
David S. Knopman, MD, professor of neurology at the Mayo Clinic College of Medicine in Rochester, MN, said it was particularly important that researchers could analyze data on incident cases — subjects who developed dementia during the course of the study — as well as prevalent cases, those already demented at the start of the study.
“The diagnosis is more reliable in incident cases, as is the dietary history,” he said. “Taking a dietary history from someone who is already impaired may not be as reliable as from someone who is cognitively intact.”
Dr. Knopman pointed out the limits of epidemiological research: the findings of the study simply show an association between adherence to a Mediterranean diet and lower mortality rates for people with AD, so the diet doesn't necessary cause the decreased risk of death.
He said there could be other explanations for the reduced mortality. One is that following the diet boosts general health and has nothing specifically to do with AD. The other is that adherence to the Mediterranean diet is not the cause of the reduced mortality, but a marker for some other health behavior that is, such as staying physically active.
“That's the problem with epidemiology,” Dr. Knopman said. “It can only show associations. It can't prove a cause, nor can it prove you've got the right fish on the line.”
Dr. Scarmeas said that though there is a wealth of information showing the Mediterranean diet is associated with lower risk of cardiovascular disease, diabetes, obesity, certain cancers, and overall mortality, he agrees the epidemiological nature of the study leaves unanswered questions. “There is a good biological background suggesting cause and effect, but on the other side, people who follow healthier diets generally have better lifestyles their whole lives. So it's not easy to say it's the diet itself,” he said.
James E. Galvin, MD, MPH, associate professor of neurology, psychiatry, and neurobiology and the director of the Memory Diagnostic Center and Alzheimer Treatment Unit at the Washington University School of Medicine in St. Louis, MO, said the study gives yet another reason for people to follow a Mediterranean-style diet, which also may help prevent cardiovascular disease and cancer.
Dr. Galvin, who authored an editorial published along with the study, said there are limits to the reliability of the study's findings, which are based on diet questionnaires. “People are likely to report they eat healthy food, even when they're eating Fritos and Twinkies every day,” he said. “They say what they think interviewers want to hear.”
Dr. Galvin also pointed out that even as the evidence mounts that diet is key to preventing a variety of medical problems, the challenge of actually getting people to eat healthier foods remains a difficult one.
Inner city populations don't always have easy access to grocery stories with fresh, affordable produce, he said. He has also observed that senior citizens increasingly rely on fast food restaurants for social gathering places.
“They don't want to prepare food at home alone, and so the most reasonable place seems to be a fast food restaurant, where they'll consume refined sugars and saturated fats,” he said. “For those who have Alzheimer disease, this could be taking time off their life span.”
The study results also prompt a tricky ethical question: Is it worth it to try to prolong survival in AD patients, whose quality of life may be in rapid decline? “Some would prefer to do everything possible to prolong life, while others consider life not worth living unless they are operating at a high functional level,” Dr. Scarmeas said.
He said one way to address that question is further research into the impact of the Mediterranean diet on the progression of AD symptoms. “We have not yet looked in detail about whether higher adherence to the Mediterranean diet affects the rate of decline in cognitive skills and other quality of life measures,” he said.