MONDAY, July 12 (HealthDay News) -- Three new studies suggest that vitamins D and E might help keep our minds sharper, aid in warding off dementia, and even offer some protection against Parkinson's disease, although much more research is needed to confirm the findings.

In one trial, British researchers tied low levels of vitamin D to higher odds of developing dementia, while a Dutch study found that people with diets rich in vitamin E had a lower risk of developing dementia, including Alzheimer's disease.

Finally, a study released by Finnish researchers linked high blood levels of vitamin D to a lower risk of Parkinson's disease.

In the first report, published in the July 12 issue of the Archives of Internal Medicine, a research team led by David J. Llewellyn of the University of Exeter in the United Kingdom found that among 858 older adults, those with low levels of vitamin D were more likely to develop dementia.

In fact, people who had blood levels of vitamin D lower than 25 nanomoles per liter were 60 percent more likely to develop substantial declines overall in thinking, learning and memory over the six years of the study.

In addition, they were 31 percent more likely to have lower scores in the test measuring "executive function" than those with sufficient vitamin D levels, while levels of attention remained unaffected, the researchers found. ("Executive function" is a set of high-level cognitive abilities that help people organize, prioritize, adapt to change and plan for the future.)

"The association remained significant after adjustment for a wide range of potential [factors], and when analyses were restricted to elderly subjects who were non-demented at baseline," Llewellyn's team wrote.

The possible role of vitamin D in preventing other illnesses has been investigated by other researchers, but one expert cautioned that the evidence for taking vitamin D supplements is still unproven.

"There is currently quite a lot of enthusiasm for vitamin D supplementation, of both individuals and populations, in the belief that it will reduce the burden of many diseases," said Dr. Andrew Grey, an associate professor of medicine at the University of Auckland in New Zealand and co-author of an editorial in the July 12 issue of the Archives of Internal Medicine.

"This enthusiasm is predicated upon data from observational studies -- which are subject to confounding, and are hypothesis-generating rather than hypothesis-testing -- rather than randomized controlled trials," Grey said. "Calls for widespread vitamin D supplementation are premature on the basis of current evidence."

In another report involving vitamin D and brain health, researchers led by Paul Knekt and colleagues at the National Institute for Health and Welfare in Helsinki, Finland, found that people with higher serum levels of vitamin D appear to have a lower risk of developing Parkinson's disease.

Their report was published in the July issue of the Archives of Neurology.

For the study, Knekt and his team collected data on almost 3,200 Finnish men and women aged 50 to 79 who did not have Parkinson's disease when the study began.

Over 29 years of follow-up, 50 people developed Parkinson's disease. The researchers calculated that people with the highest levels of vitamin D had a 67 percent lower risk of developing Parkinson's disease compared with those with the lowest levels of vitamin D.

"In conclusion, our results are in line with the hypothesis that low vitamin D status predicts the development of Parkinson's disease," the researchers wrote.

"Because of the small number of cases and the possibility of residual [factors that might influence the results], large cohort studies are needed. In intervention trials focusing on effects of vitamin D supplements, the incidence of Parkinson's disease merits follow up," Knekt and colleagues added.

Dr. Marian Evatt, an assistant professor of neurology at Emory University and author of an accompanying editorial, said that "vitamin D regulates a tremendous number of physiologic processes critical for normal growth, development and survival of human cells, and animal data suggests that this includes development, growth and survival of cells in the nervous system."

However, the animal data also suggests that there may be a range of vitamin D levels that are optimal and if cells are exposed to levels above or below that level, life is not so good, she said.

This study is the first study examining vitamin D levels in a population, then looking at whether there is subsequent associated risk of developing Parkinson's disease, Evatt added.

"Further studies are warranted to see if these findings can be duplicated in other populations," Evatt concluded.

Still another report, published in the July issue of the Archives of Neurology, found that eating foods rich in vitamin E might help stave off dementia and Alzheimer's disease. These foods included margarine, sunflower oil, butter, cooking fat and soybean oil.

For the study, researchers led by Elizabeth E. Devore, from Erasmus Medical Center in Rotterdam, the Netherlands, collected data on the diets of almost 5,400 people 55 years and older who did not have dementia between 1990 and 1993. Over an average of 9.6 years of follow-up, 465 of these individuals developed dementia, and 365 of these were diagnosed with Alzheimer's disease, the researchers reported.

Devore's team found that those who consumed the most vitamin E (one-third of the participants) were 25 percent less likely to develop dementia, compared with the third who consumed the least.

"The brain is a site of high metabolic activity, which makes it vulnerable to oxidative damage, and slow accumulation of such damage over a lifetime may contribute to the development of dementia," Devore and colleagues wrote.

"In particular, when beta-amyloid (a hallmark of pathologic Alzheimer's disease) accumulates in the brain, an inflammatory response is likely evoked that produces nitric oxide radicals and downstream neurodegenerative effects. Vitamin E is a powerful fat-soluble antioxidant that may help to inhibit the pathogenesis of dementia," the authors added.

The researchers concluded that further studies are needed to evaluate the possible benefits of dietary intake of antioxidants.

Dr. Michael Holick, a professor of medicine, physiology and biophysics and director of the General Clinical Research Center at Boston University Medical Center said that "these finding are consistent with what we have been believing for a long time, that the brain has receptors for vitamin D, so to maximize brain function you probably need adequate vitamin D."

Holick also believes that vitamin E is probably important for brain health. "It may be that vitamin E improves the health of the brain cell," he said.

More information

For more information on vitamin D, visit the U.S. National Institutes of Health.