THURSDAY, Aug. 31 (HealthDay News) -- The risk of developing Alzheimer's disease was dramatically reduced for older people who drank fruit or vegetable juices regularly in a 10-year study, researchers report.
The incidence of Alzheimer's was 76 percent lower for those who drank juice three or more times a week than for those who drank juice less than once a week. It was 16 percent lower for those drinking juice once or twice a week, according to the report.
It's not the general kind of antioxidants in fruit juices that produce the benefit, said Dr. Qi Dai, assistant professor of medicine at Vanderbilt University School of Medicine and lead author of the report. Rather, he attributed the effect to polyphenols, a particularly strong antioxidant.
"That is why we chose to look at fruit and vegetable juice," Dai said. "They [polyphenols] are found in the outer sections of fruits and vegetables, only in the peel or skin. When you process the whole fruit, they go into the juice."
Studies of the biochemistry of Alzheimer's disease have focused on deposits of beta-amyloid proteins that form in the brain and the potential for antioxidants in the diet to prevent those deposits, Dai said. But studies looking at antioxidants such as beta-carotene have been disappointing, "so we thought maybe some other components in fruits and vegetables account for the reduced risk," he said.
The study followed more than 1,800 participants in the Kame Project, a research project of Japanese people and their health who live in Hiroshima, Japan; Oahu, Hawaii; and Seattle. They reported on their consumption of fruit and vegetable juice starting in 1992, and their mental function was tested every two years thereafter.
The reduction in incidence of Alzheimer's disease in those who regularly consumed juice "was stronger after adjustments for potential confounding factors, and the association was evident in all strata of selected variables," the report said.
The findings were published in the September issue of the American Journal of Medicine.
More research needs to be done to determine whether specific juices or specific polyphenols produce the most benefit, Dai said. "We are applying for a National Institutes of Health grant for further study to see which juices play a more important role," he said. "We have blood samples and can do additional studies to see blood markers of polyphenols and which polyphenol is most important."
Bill Thies, vice president for medical and scientific relations at the Alzheimer's Association, called Dai's research "a reasonable theory that has some fundamental chemistry to back it up. But there is a lot more work to be done in humans."
Thies pointed to one possible weak point in the study. "There were only a little more than 80 cases of dementia, so how precise the relationship is may be adjusted over time," he said.
Summing up, Thies said: "If you like juice, this is a good reason to drink it. But we'd be a little careful not to drive people down the road, saying, 'If I drink orange juice in the morning, I don't have to do anything else.' "