VITAMIN D RESOURCE

July 15, 2010 — In the first longitudinal analysis of its kind, investigators have identified a link between vitamin D and Parkinson's disease. Using a cohort of more than 3000 people, researchers found that low vitamin D levels increased the risk for Parkinson's, and high rates appeared to have a protective effect.

The preliminary findings appear in the July issue of the Archives of Neurology.

"This study was carried out in Finland, an area with restricted sunlight exposure," noted researchers led by Paul Knekt, DPH, from the National Institute for Health and Welfare in Helsinki, Finland. It is a population that typically has low vitamin D levels. The mean serum level was about 50% of the suggested optimal level of 75 to 80 nmol/L, the authors explained.

"Vitamin D is no longer considered a vitamin, but rather a hormone that has autocrine and paracrine functions well beyond those of regulating calcium absorption and bone health," Marian Leslie Evatt, MD, from Emory University in Atlanta, Georgia, said in an accompanying editorial.

"The association with and possible causal role of insufficient vitamin D in many chronic diseases is becoming more widely appreciated yet what constitutes an optimal blood concentration of vitamin D for humans, and specifically for the human nervous system, remains unknown," she noted.

Vitamin D is no longer considered a vitamin, but rather a hormone that has autocrine and paracrine functions.

To investigate the possible association between vitamin D and Parkinson's, investigators studied a large cohort from the Mini-Finland Health Survey, drawn from the population register. During the 29-year follow-up period, there were 50 incident cases of Parkinson's disease.

Researchers determined serum 25-hydroxyvitamin D levels using frozen samples stored at baseline. They estimated the relationship between vitamin D concentration and Parkinson's disease using a Cox model.

The investigators found that individuals with a serum vitamin D concentration of at least 50 nmol/L had a 65% lower risk for Parkinson's than those with values less than 25 nmol/L after adjustment for several potential confounders. The relative risk between the highest and lowest vitamin D levels was 0.35 (95% confidence interval, 0.15 - 0.81; P = .006).

Despite the overall low vitamin D levels in the study population, the researchers also identified a dose-response relationship.

Preliminary Findings

The exact mechanisms by which vitamin D may protect against Parkinson's disease are not fully understood. Vitamin D has, however, been shown to exhibit neuroprotective effects through antioxidative mechanisms, neuronal calcium regulation, immunomodulation, enhanced nerve conduction, and detoxification mechanisms.

The investigators acknowledge the finding could be a result of residual confounding, and further studies are needed.

It seems like every time I turn around, I'm reading another association study.

Asked by Medscape Medical News to comment, William Weiner, MD, director of the Maryland Parkinson's Disease and Movement Disorders Center in Baltimore, said he agrees that more study is warranted.

"It seems like every time I turn around, I'm reading another association study in the field of neurology," Dr. Weiner said. "We're being told we need more of this or less of something else. Patients tend to get excited about these findings, but we need to be very cautious because most will not turn out."

Dr. Weiner said he agrees such studies should be conducted and published, but he says the caveats must be emphasized. "It's important we let people know how early these investigations are."

The researchers, Dr. Evatt, and Dr. Weiner have disclosed no relevant financial relationships.