Diets that are rich in vitamin E may help to protect against Parkinson's, the neurodegenerative disease that afflicted

People who had moderate to high amounts of vitamin E in their diets were less likely to develop Parkinson's, while vitamin C and beta carotene seemed to have no effect, it says.

But pills and other supplements of vitamin E -- as opposed to vitamin E that occurs naturally in food -- may not have this protective effect, it says.

The paper is a so-called meta-analysis, in other words, an overview of previous studies that have been carried out into Parkinson's and nutrition.

Its authors trawled through two big databases to find eight research projects in this area, spanning 1966 to March 2005.

People who had a pronounced intake of vitamin E in their diets were 19 percent less likely to develop Parkinson's.

Vitamin E is found in vegetable oils, nuts and green leafy vegetables, such as spinach and broccoli, as well as peanut butter and fruit such as kiwi and mangoes, according to the US

The study is published online by The Lancet Neurology, a specialist journal that is a stablemate of the British medical weekly The Lancet.

Its authors, led by Mahyar Etminan, of the Royal Victoria Hospital and McGill University in Montreal, Canada, are cautious about drawing firm conclusions given that only a small number of studies into the impact of vitamins on Parkinson's have been assessed.

They warn that, before doctors recommend any shift in diets, the results would have to be confirmed by a large trial to compare the outcome of matched people who have different levels of dietary vitamin E and are then monitored to see whether they develop the disease.

Parkinson's is a currently incurable, degenerative disease of the nervous system, affecting more than one percent of people over the age of 65.

It occurs when there is a loss of cells in a part of the brain that produces dopamine, a neurotransmitter that communicates with other brain cells which regulate motor functions. Symptoms range from tremors and awkwardness and muscular stiffness to a distinctive shuffling gait.

The cause of the cell loss is unknown.

The current speculation is that a basket of factors -- ageing, genetic predisposition and environmental exposure -- may be to blame.

One area of research is into oxidative stress: the creation of rogue molecules called free radicals that are associated with cell damage. Vitamins are called antioxidants for their ability to combat these dangerous agents.

The authors suggest that vitamin E may be more effective in naturally-occurring form rather than as a supplement because it is a slightly different molecule that is more "bioactive" than its synthetic counterpart.

As to why vitamin C -- a highly powerful antioxidant -- does not appear to combat the risk of Parkinson's, the authors suggest that the molecule may get filtered out by barriers to the brain, thus diminishing its "neuroprotective potential."