By Andrew M. Seaman
NEW YORK (Reuters Health) - Depending on their genes, some Parkinson's patients may be able to slow their deterioration by taking vitamin D supplements, according to a small study from Japan.
Researchers randomly assigned 114 people with Parkinson's disease to take either vitamin D or a placebo every day for a year and found the neurologic condition didn't progress as much in those who took the supplements, compared to those who took placebos. But that was only true for people with certain versions of a gene for the vitamin D receptor.
Dr. Lin Zhang, who was not involved in the work but studies nutritional deficiencies in people with Parkinson's called the findings "very promising," but urged caution in interpreting the results.
"We are just starting to recognize the potential benefit of vitamin D in slowing down the progression of Parkinson's disease, and we have no way of knowing the exact dosage one person should take with or without such genotypes," said Zhang, from the University of California, Davis.
Previous studies have found that people with Parkinson's disease have low levels of vitamin D circulating in their blood, though none have established whether the vitamin deficiency is a cause or effect of the disease.
The body produces vitamin D from sunlight exposure and uses it to help get calcium into bones, among other functions. The vitamin itself activates a receptor protein in cells that triggers the activity of a variety of genes.
For the new study, researchers recruited 114 Parkinson's patients between 45 and 85 years old to see whether taking vitamin D supplements would change how fast the symptoms of Parkinson's disease progressed.
Of those, 56 patients took 1,200 international units of vitamin D per day for 12 months, and 58 took placebos for the same length of time.
At the beginning of the study, about 45 patients in each group scored a 1 or 2 on a five-point scale that measures disability from Parkinson's disease. A score of 1 represents the least disability, while a 5 is bedridden.
Measures of disability include whether or not a person has impaired movement, trouble balancing and can get around on their own.
At the end of the year, the researchers found that 16 people in the group taking the supplements didn't get worse on the five-point scale, compared to 7 people whose symptoms were stable in the group taking the placebo.
But when they looked at the patients' vitamin D receptor genes, the researchers found that people with the gene version known as FokI TT benefited the most from supplements, followed by those with the FokI CT variant, compared to people in the placebo group. People with the FokI CC genotype did not benefit at all.
Similar results were seen for another measure of Parkinson's symptoms, according the report in The American Journal of Clinical Nutrition.
Zhang told Reuters Health the results suggest that people with the FokI TT and FokI CT variants respond to the additional vitamin D better than those with the FokI CC version of the gene.
Just 14 percent of the study participants had the TT gene version, while 52 percent had the CT genotype and 34 percent had the CC version of the gene. Those proportions are in keeping with most populations, where between 8 percent and 18 percent of people have the TT variant, according to the researchers, and between 46 percent and 58 percent of non-Asians have the CT variant.
There were no differences in the starting levels of circulating vitamin D among the study participants, and about half began with levels considered deficient. All the patients who got the supplements more or less doubled the amount of D in their bloodstream by the end of the study while the levels in the placebo group didn't change.
The large number of participants taking vitamin D whose symptoms did not get worse over the course of the year suggests that vitamin D supplementation may stabilize "the severity of Parkinson's disease in patients with FokI CT and TT genotypes for a short period of time," the study authors conclude.
But there are still unanswered questions. Among them, what effect of vitamin D might account for the symptom differences seen at the end of the study.
Past research has found the vitamin can improve muscle strength and balance in elderly people, for example. So the researchers said they cannot be sure whether the patients' Parkinson's did not progress in people who took the D supplements or their balance just improved.
"If we do the same trial by targeting an older generation without Parkinson's disease and get the same results, that suggests the effect we observed in this study was due to just improving balance," said Dr. Mitsuyoshi Urashima, the study's senior author from Jikei University School of Medicine in Tokyo, in an email to Reuters Health.
Until more trials are done, Zhang said there are too many variables to issue a blanket recommendation for all Parkinson's patients to take vitamin D.
"The bottom line is there are so many other factors to take into consideration," he said.
SOURCE: http://bit.ly/16XRHrP The American Journal of Clinical Nutrition, online March 13, 2013.