Two new studies offer preliminary evidence that dietary choices could help prevent age-related mental decline or slow its progression.
In one, people who followed the so-called Mediterranean diet, which includes plenty of fruits and vegetables but little red meat, had a lower risk of developing Alzheimer's than people who did not follow the diet. In the other, taking omega-3 fatty acid supplements seemed to slow disease progression in people with very early Alzheimer's disease.
Population-based studies and trials in animals have long suggested that Alzheimer's risk may be influenced by diet. But there have been few direct studies in humans examining whether diet and other lifestyle factors play a role in the disease.
"We have identified genes that may be responsible for 2% to 3% of Alzheimer's cases, but in the vast majority of cases we don't know what causes this disease," Nikolaos Scarmeas, MD, of Columbia University, tells WebMD.
"Certainly, there may be genetic predispositions that we haven't discovered yet. But there is plenty of room for environmental influences, like diet, to play a role."
Lowering Risk With Olive Oil
Scarmeas and colleagues first reported a link between the Mediterranean diet and Alzheimer's risk in a study involving 2,258 New Yorkers published in June in the Annals of Neurology.
In an effort to confirm the findings, the Columbia University researchers repeated the trial in roughly 2,000 people who either had the disease or were at risk for developing it. The average age of the participants was 76, and roughly one in 10 had a diagnosis of Alzheimer's disease.
The researchers reviewed the diets of all study participants over the course of a year to determine how closely the subjects adhered to the principles of the Mediterranean diet.
Long suspected of lowering the risk of heart disease and diabetes, the Mediterranean diet consists of large amounts of fruits, vegetables, beans, grains, and nuts. Red meats are eaten only rarely and poultry, eggs, and dairy products are eaten in moderation. Olive oil and fatty fish are the main sources of fat in the diet.
Just as with their previous study, Scarmeas and colleagues found that people who most closely followed the Mediterranean model had the lowest Alzheimer's risk.
People who most closely adhered to the diet had an Alzheimer's risk that was 40% to 65% lower than people who were least likely to follow the diet, Scarmeas tells WebMD.
The study was published today in an advance online issue of the journal Archives of Neurology.
Fatty Fish and Alzheimer's
In a separate study, published in the October issue of Archives of Neurology, researchers from Sweden's Karolinska Institute and Uppsala University Hospital investigated the potential benefits of treating Alzheimer's patients with omega-3 supplements.
The overall results were disappointing, with no difference seen in the rate of mental decline between 204 patients with mild to moderate Alzheimer's disease who did and did not take the supplements for six months.
But a positive benefit was seen among the 32 patients in the study with very mild mental decline identified at the beginning of the study. These patients experienced less rate of decline in mental function than similarly functioning patients who took placebo capsules that did not contain omega-3 fatty acid.
Patients who took the placebo capsules during the first six months of the trial were switched to the omega-3 supplements for another six months. During this second phase of the trial, patients with mild disease seemed to experience a slowing of disease progression.
Tommy Cederholm, MD, PhD, of Uppsala University Hospital characterizes the effect as "clinically relevant, but not dramatic," in an interview with WebMD.
"This could ba chance finding," he says. "We need larger studies to answer this question."
Several larger studies are under way, prompted by promising animal research and research showing a lower incidence of Alzheimer's disease in populations that regularly eat omega-3-rich fish.
In the meantime, Cederholm says it is far too early to recommend fish oil supplements for people with Alzheimer's or those at risk for developing the disease. But he adds that eating fatty fish such as salmon, trout, and tuna regularly may help lower Alzheimer's risk and the risk of other chronic diseases.
SOURCES: Levi-Freund, Y. Archives of Neurology, October 2006; vol 63: pp 1402-1408. Scarmeas, N. Archives of Neurology, Oct. 9, 2006; advanced online edition. Tommy Cederholm, MD, PhD, department of public health and caring sciences, clinical Nutrition and metabolism, Uppsala University Hospital, Uppsala, Sweden. Nikolaos Scarmeas, MD, Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Columbia University Medical Center, New York.
By Salynn Boyles
Reviewed by Louise Chang