WASHINGTON — Greater levels of vitamin D have been linked to a lower risk of Parkinson's disease in a study in Finland where low sunlight leads to a chronic lack of the nutrient, researchers said Monday.

Scientists from the National Institute for Health and Welfare, Helsinki, Finland, first hypothesized that Parkinson's "may be caused by a continuously inadequate vitamin D status leading to a chronic loss of dopaminergic neurons in the brain."

Vitamin D, supplied chiefly by the sun's ultraviolet rays and a small range of foods, is known to play a role in bone health and may also be linked to cancer, heart disease and type 2 diabetes, the researchers said.

The Finnish study, published in the July issue of Archives of Neurology, followed 3,173 Parkinson's-free Finnish men and women aged 50-79 over a 29-year period from 1978-2007.

At the end of the study 50 participants had developed the disease.

After adjusting for potentially related factors, including physical activity and body mass index, those with the highest levels of vitamin D (top 25 percent of the group) were found to have a 67 percent lower risk of developing Parkinson's disease than those with the lowest level of the vitamin (bottom 25 percent), the study said.

The researchers could not explain how vitamin D levels may affect Parkinson's risk, but said the nutrient "has been shown to exert a protective effect on the brain through antioxidant activities, regulation of calcium levels, detoxification, modulation of the immune system and enhanced conduction of electricity through neurons."

"In intervention trials focusing on effects of vitamin D supplements, the incidence of Parkinson disease merits follow up," they added.

"This study was carried out in Finland, an area with restricted sunlight exposure, and is thus based on a population with a continuously low vitamin D status," about half of the suggested optimal level, researchers said.