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NASHVILLE, Tenn. -- A glass of fruit or vegetable juice every other day may help fend off Alzheimer's disease, a prospective study of older Japanese-Americans suggested.
NASHVILLE, Tenn., Aug. 31 -- A glass of fruit or vegetable juice every other day may help fend off Alzheimer's disease, a prospective study of older Japanese-Americans suggested.
Compared with those who averaged less than one glass of juice per week, those who drank three or more were 76% less likely to develop Alzheimer's disease, reported Qi Dai, M.D., Ph.D., of the Vanderbilt School of Medicine here.
"These findings are new and suggest that fruit and vegetable juices may play an important role in delaying the onset of Alzheimer's disease," Dr. Dai and colleagues said in the September issue of The American Journal of Medicine.
Recent studies of antioxidant vitamins for preventing Alzheimer's have been disappointing, despite the initial promise of these vitamins, the investigators said. Therefore, the current study explored fruit and vegetable juices, which are an abundant source of polyphenols, they said.
Polyphenols are usually found in the skin and peel of fruits and vegetables. Previous research has shown that when fruits and vegetables are mechanically squeezed to make juice, high concentrations of polyphenols from the peel and pulp get into the juice, the investigators said.
Although the current study did not identify the kinds of juices participants consumed, previous studies have shown that apple, grape, and citrus fruit juices are high in polyphenols, they added.
The current study, part of the Kame Project, included nearly 2,000 dementia-free Japanese-Americans living in the Seattle area. Their average age was nearly 72, and they were roughly half men and half women. Alzheimer's is relatively uncommon in Japan, but its prevalence has been rising in Japanese-Americans, suggesting environmental and lifestyle factors may be at play, the investigators said.
Participants completed a food frequency questionnaire and underwent clinical evaluation at baseline in 1992-1994. They then underwent clinical evaluation for Alzheimer's every two years through 2001.
After adjusting for potential confounders such as age, gender, BMI, education, vitamin intake, smoking, and more, those who drank three or more serving of juice weekly were at significantly reduced risk for Alzheimer's (hazard ratio=0.24; 95% confidence interval=0.09 to 0.61; P<.01), the study found.
Even those who drank only one or two serving weekly had some protection compared with those who consumed less juice (HR=0.84; 95% CI=0.31 to 2.29).
The study results were actually stronger, not weaker, after adjusting for the potential confounders. Before adjustment, the hazard ratio for those drinking three or more juice servings per week was only 0.49 (95% CI=0.28 to 0.86; P<.01).
Dietary consumption of vitamins E, C, and beta-carotene were not related to Alzheimer's risk, the investigators said. These data were not presented.
The association tended to be stronger among those who were former or current smokers, drank tea less often, were less physically active, and were positive for the e-4 allele of apolipoprotein E. Previous research has suggested that all of these factors may be linked to Alzheimer's risk.
The oxidative damage to brain tissue in Alzheimer's may be mediated by hydrogen peroxide, and polyphenols may offer stronger neuroprotection against hydrogen peroxide than antioxidant vitamins, the investigators speculated.
Despite the promising results, the public should not jump to the conclusion that fruit and vegetable juice will prevent Alzheimer's, Dr. Dai said. "A few years ago, hormone replacement therapy, NSAIDs, and antioxidant vitamins showed promise, but recent clinical trials indicate that they do not," he said. "More study, I think, is needed."
Future studies will attempt to confirm these results by measuring blood levels of polyphenols in juice drinkers and examining the relation between these levels and Alzheimer's risk, the authors said.
The study was supported by a grant from the National Institute on Aging.