Eating nuts, leafy green vegetables and other foods rich in antioxidants such as vitamin E may reduce the risk of Alzheimer's, two studies suggest.
The findings build on growing research into the effects of antioxidants on dementia.
The latest studies seem to suggest that vitamin-rich foods, but not vitamin supplements, have beneficial effects. The researchers, however, said more definitive studies are needed.
The connection, at least, is considered plausible: Antioxidant vitamins have been shown to block the effects of oxygen molecules called free radicals, which can damage cells and are thought to contribute to cancer and heart disease. And lesions typically associated with exposure to free radicals have been found in the brains of Alzheimer's patients.
One of the studies found strong effects from vitamins E and C. In the other, results from vitamin E foods were more conclusive, but researchers said there was a suggestion vitamin C also provided benefits.
Previous research suggested that vitamin E pills could slow disease progression in people already diagnosed with Alzheimer's. The new studies examined people who had not developed the mind-robbing ailment at the outset and suggested no effect from pills. But pill use was somewhat uncommon and of comparatively short duration in both studies.
The studies appear in Wednesday's Journal of the American Medical Association.
One study, funded by the National Institute on Aging, involved 815 Chicago residents 65 and older who had no initial symptoms of mental decline. They were questioned about their eating habits and followed for an average of about four years.
Alzheimer's developed in 131 participants. It was diagnosed in 14.3 percent of those with the lowest intake of vitamin E foods, compared with 5.9 percent of those with the highest intake. When factors such as age and education were taken into account, the highest-intake group faced a 70 percent lower risk of developing the disease.
Intake of vitamin C, found in foods such as citrus fruits, also appeared to have offer some protection, but those results were not statistically significant, said lead researcher Martha Clare Morris of Rush-Presbyterian-St. Luke's Medical Center in Chicago.
Morris said participants with the highest vitamin E intake ate amounts that could be obtained from a diet that includes whole-grain cereal for breakfast, a sandwich with whole-grain bread for lunch and a dinner including a green leafy salad sprinkled with nuts.
There was no protective effect in participants with a gene variation called apoplipoprotein E-4, which has been linked to the development of Alzheimer's.
The other study, from Erasmus Medical Center in Rotterdam, involved 5,395 people in the Netherlands 55 and older who were followed for an average of about six years.
Alzheimer's developed in 146 participants. Those with high intakes of vitamins E and C were less likely to become afflicted, regardless of whether they had the gene variation.
"The idea that vitamin E and vitamin C might have beneficial effects on the underlying Alzheimer's disease process makes sense, and it seems unlikely that antioxidant-rich foods would negatively affect brain aging," Daniel Foley of the National Institute on Aging and Dr. Lon White of Pacific Health Research Institute in Honolulu said in an accompanying editorial.
Still, they noted several limitations in both studies, including relying on participants' memories of their eating habits and not following them longer.
National Institute on Aging scientist Neil Buckholtz said several NIA-funded studies are attempting to help answer whether antioxidants in food or pills affect mental decline.