A vitamin D shortage is more likely to show up in people with Parkinson’s disease than in healthy people or those with Alzheimer’s disease, scientists report in the October Archives of Neurology. The study is the most recent contribution to a torrent of findings linking vitamin D deficiency with health risks.
It’s well documented that such a deficiency can cause osteoporosis. Studies in recent years have also implicated a shortage of vitamin D in heart disease, stroke, multiple sclerosis, cancer and even respiratory problems.
In the new study, researchers measured vitamin D levels in blood samples obtained between 1992 and 2007 from 100 randomly selected Parkinson’s patients. The scientists also analyzed blood samples from 97 Alzheimer’s patients and 99 healthy people from that same time frame.
The team sampled Alzheimer’s patients to assess vitamin D deficiency in another neurodegenerative disorder other than Parkinson’s disease. The groups were similar in race, geographical residence (in the southeastern United States) and age (mid-60s on average).
People with less than 30 nanograms of vitamin D per milliliter of blood were deemed deficient. The analysis showed that 55 percent of the Parkinson’s patients fell into this category, compared with 41 percent of the Alzheimer’s patients and 36 percent of the healthy control group.
People make vitamin D when exposed to sunshine. The differences in the participants’ blood levels could be because Parkinson’s patients get outdoors less often than others, says study coauthor Marian Evatt, a neurologist at EmoryUniversity in Atlanta. Further studies will clarify that question, she says.
But previous research has hinted that a shortage of vitamin D could affect brain areas associated with Parkinson’s disease, the study’s authors note. Parkinson’s disease results when a person loses neurons that make dopamine in a part of the brain called the substantia nigra. Dopamine is a neurotransmitter that orchestrates motor activity and other processes. Lack of dopamine is a central trait of Parkinson’s.
Vitamin D exerts its effects throughout the body by attaching to vitamin D receptors on cells. Neurons in the substantia nigra display vitamin D receptors in abundance, Evatt says. “If you’ve got tissues or cells with high concentrations of … vitamin D receptors, that indicates there’s a local function that vitamin D is providing in that area,” she says.
When it binds to a receptor protein on a cell, vitamin D activates or turns off as many as 800 genes, depending on the challenge the cell is facing, says endocrinologist Robert Heaney of CreightonUniversity in Omaha, Neb. These challenges range from fending off bacteria to rebuilding tissues.
“This helps to explain why we’re finding vitamin D having effects in such diverse tissues,” he says. It’s not clear what the vitamin’s precise role in the substantia nigra is, he says. “But if vitamin D is part of a cell’s ability to respond to a signal, that response will be blunted in the absence of vitamin D,” he reasons.
Meanwhile, in a separate study, the researchers are checking vitamin D levels at the very first signs of Parkinson’s disease, says study coauthor Vin Tangpricha, an endocrinologist at Emory.
Evatt ML et al. Prevalence of Vitamin D Insufficiency in Patients With Parkinson Disease and Alzheimer Disease. 2008. Archives of Neurology, October, Vol. 65. p. 1348-1352.
Holick MF. Vitamin D deficiency. 2007. New England Journal of Medicine, Vol. 357, p. 266-281.
Sato Y, et al. High prevalence of vitamin D deficiency and reduced bone mass in Parkinson’s disease. 1997. Neurology, Vol. 49, p. 1273-1278.