People who eat a "Mediterranean" diet rich in fruits, vegetables, olive oil, legumes, cereals and fish, have a lower risk of developing Alzheimer's disease, US researchers report.
"We have confirmed the association of a Mediterranean diet with Alzheimer's disease," said lead researcher Dr Nikolaos Scarmeas, an assistant professor of neurology at Columbia University Medical Centre in New York.
This benefit does not appear to be due to the diet's effect on blood vessels, Scarmeas added. "The diet could be helping avoid Alzheimer's disease by protection from oxidative stress or by reducing inflammation in the brain," he said.
Omega-3 slows decline
Another study finds that taking omega-3 fatty acid supplements slows cognitive decline in some patients with very mild Alzheimer's disease. However, supplements do not appear to affect people with more advanced cases of the disease, according to a team of Swedish researchers.
Both reports appear in the online October issue of the Archives of Neurology.
For the diet study, Scarmeas's team collected data on almost 2 000 people averaging 76 years of age. Of these, 194 had developed Alzheimer's. The researchers analysed each person's diet during the previous year. They scored the diet based on how closely it followed what's known as the Mediterranean diet, which also includes mild-to-moderate drinking and little intake of red meat. Scores ranged from zero to nine. Higher scores were given for closely following a Mediterranean diet.
Significant decrease in risk
People who closely followed that regimen had a significantly lower risk for Alzheimer's disease, the researchers found. For each additional point on the diet score, risk for Alzheimer's was reduced by 19 to 24%.
In fact, people in the top one-third of diet scores had 68% lower risk of developing Alzheimer's disease, compared with people in the bottom third. In addition, people in the middle third had a 53% lower risk of developing the disease.
While the jury is still out on whether a Mediterranean diet actually protects people from developing Alzheimer's disease, Scarmeas believes that the other health benefits of the diet are clear.
Various benefits to med diet
"It seems that this diet is [health] protective," Scarmeas said. "Taking into account that this diet is protective for other conditions such as coronary heart disease, heart attack, high blood pressure, obesity and a series of cancers, it seems to make sense to follow this diet anyway, and the diet may also protect from Alzheimer's disease."
In the second report, a team led by Dr Yvonne Freund-Levi from the Karolinska Institutet in Stockholm, looked at the effects of omega-3 fatty acids supplements on 204 patients with Alzheimer's disease.
After six months, among the 174 people who completed the trial, the researchers found no difference in cognitive decline among people taking omega-3 fatty acids supplements at different doses or placebo.
However, for a subgroup of 32 patients with very mild cognitive impairment at the beginning of the study, those taking the supplements experienced less cognitive decline compared with those who took placebo, the researchers found.
And when patients who took placebo during the first six months were given omega-3 fatty acids supplements, their cognitive decline decreased during the second six months of the trial.
Mechanisms still unclear
"The mechanisms by which omega-3 fatty acids could interfere in Alzheimer's disease pathophysiologic features are not clear, but since anti-inflammatory effects are an important part of the profile of fish oils, they are conceivable also for Alzheimer's disease," the researchers write. "It is possible that when the disease is clinically apparent, the neuropathologic involvement is too advanced to be substantially attenuated by anti-inflammatory treatment."
One expert said that, given the other health benefits of fish oil, it certainly can't hurt patients to take supplements.
"I am happy to tell people that if they want to reduce their risk for Alzheimer's, they should reduce their cardiovascular disease risk factors and take fish oil," said Greg M. Cole, a neuroscientist at the Greater Los Angeles VA Healthcare System, and the associate director of the Alzheimer's Disease Research Centre at UCLA's David Geffen School of Medicine.
Diet tied to Alzheimer's
A second expert agreed that diet probably does influence the disease.
"The papers share a focus on the idea that diet plays a role in Alzheimer's, a consensus that has been building for the past five or six years," said Dr Sam Gandy, the chair of the Medical and Scientific Advisory Council at the Alzheimer's Association and director of the Farber Institute for Neurosciences at Thomas Jefferson University.
"The common thread is that both papers point toward intervention at the earliest moment having a greater effect and the suggestion that prevention may have the greatest effect of all," Gandy said.
"Once the gooey amyloid material has accumulated and poisoned nerve cells and the cells have died, it is very hard to think seriously about repairing damage that severe," he added.