A growing body of evidence points to damage from free radicals as the cause of Alzheimer's disease. Free radicals -- byproducts of our bodies' normal functions -- can cause damage to cells, leading to cancer, heart disease, and other illnesses.
Antioxidant nutrients such as vitamin E, vitamin C, and beta carotene are among the body's natural defense mechanisms against this damage. Important sources of vitamin E are grains, nuts, milk, and egg yolk. Vitamin C is mainly found in citrus fruits, kiwi, sprouts, broccoli, and cabbage. Beta carotene is found in kale, carrots, broccoli, and spinach.
The first study followed more than 5,000 men and women -- all at least 55 years old -- for an average of six years. None had any signs of dementia at the beginning of the study. Six years later, 197 had developed dementia; 146 of them had Alzheimer's disease.
"High intake of vitamin C and vitamin E was associated with lower risk of Alzheimer's disease," writes researcher Marianne J. Engelbert, MD, MSc, epidemiologist at Erasmus Medical Center in Rotterdam, Netherlands.
Among smokers, this relationship was most pronounced; for them, beta carotene and flavonoids -- another type of antioxidant -- also seemed to have a protective effect. Those with genetic predisposition for Alzheimer's did not get any more or less protection from the vitamins.
The second study followed 815 Chicago area residents, all 65 and over, for about four years. That study suggests that vitamin E from food -- but not other antioxidants -- reduces risk of Alzheimer's.
However, the protective effect was only found among people who did not have the apoE4gene -- a genetic predisposition for Alzheimer's; a total of 131 persons developed Alzheimer's during the four-year study period.
"Surprisingly, neither study identified an association between [Alzheimer's disease] and use of vitamin E and vitamin C supplements," writes Daniel J. Foley, MS, an epidemiologist with the National Institute on Aging, in an accompanying editorial.
But one potential problem with the study is that a person with declining memory might not accurately report their diet or supplement use, he says. Also, someone who recognizes hints of memory decline might start taking supplements or eating better. Better studies are needed to look at these issues, writes Foley.
As to why no association between vitamin E and those with a genetic predisposition was found, Foley suggests that it may be because this group of people is more commonly diagnosed at an age younger than 55. Thus, they would not have been eligible for the study.
Though the two studies have similar findings, they do not provide the final answer to whether antioxidant vitamins are truly protective against Alzheimer's, Foley writes. "Nonetheless, the idea that vitamin E and vitamin C might have beneficial effects on the underlying [disease] process makes sense, and it seems unlikely that antioxidant-rich foods would negatively affect brain aging."