The role of vitamin E supplements is not clear, but at least one study suggests that synthetic supplements do not confer the same benefit as dietary sources, such as almonds and broccoli.

However, confirmation is needed from a large randomized trial before any suggestions to changes in routine clinical practice can be made, state the authors.

No Benefit from Vitamin C, Carotene

Parkinson's disease is a progressive neurodegenerative disease with unknown cause. PD is likely to result from the combined effects of multiple factors, including aging, genetic predisposition and environmental exposures.

Some studies suggest that diets rich in vitamin E are protective against PD; other studies show no such benefit.

Mayhar Etminan of the Royal Victoria Hospital, Quebec, Canada, and Center for Clinical Epidemiology and Evaluation, Vancouver, Canada, and colleagues performed a meta-analysis to try to establish whether vitamin C, vitamin E and carotene can lower the risk of PD.

The investigators searched for relevant studies from 1966 to March 2005. They combined the data from eight studies and found that moderate dietary intake of vitamin E decreased the risk of developing PD.

However, dietary vitamin C and carotene did not seem to confer any protective effects.

Synthetic Supplements May Not Be Beneficial

The role of vitamin E supplements is not clear, but at least one study suggests that synthetic supplements do not confer the same benefit as dietary sources, state the authors.

"Our data suggest that diets rich in vitamin E protect against the development of PD," said Dr. Etminan.

"No definite conclusions regarding the benefits of supplemental vitamin E can be made," he added. "Neither vitamin C nor carotene seems to have a neuroprotective effect.

"Given that these data are observational, confirmation from well-designed randomized controlled trials is necessary before suggesting changes in routine clinical practice," Dr. Etminan concluded.