No Definitive Answers on Vitamin D
Supplement Benefits for the Healthy
San Francisco, CA—Vitamin D formulations are taking up more and more space on drug store shelves, and pharmacists are getting a lot of questions these days about the health benefits of the fat-soluble secosteroids. Two recent reviews of how supplementation with the vitamin affects fractures and overall health add new information but don't really provide any unequivocal answers.
New draft findings
by the United States Preventive Services Task Force conclude that, for healthy, postmenopausal women, there is no clear-cut evidence that daily supplementation with low levels of vitamin D, defined as up to 400 international units, combined with 1,000 milligrams of calcium, reduces fracture risk. The task force also noted that supplementation at this level is associated with a small but significantly increased likelihood of developing kidney stones.
Because of the lack of high-quality studies, the task force was unable to draw conclusions about whether supplementation helps prevent bone fractures in healthy men and in premenopausal women or the vitamin's role, if any, in cancer prevention. Supplementation with higher doses also could not be evaluated because of insufficient evidence.
The group did not look at the effect of vitamin D supplementation on patients already diagnosed with osteoporosis or vitamin D deficiencies. Previously, the task force has recommended augmenting nutrition with vitamin D
to prevent falls
among men and women age 65 and older.
"We know that vitamin D and calcium are essential for a healthy diet," said task force member
, MD, PhD, a University of California San Francisco epidemiologist and internist. "We're not making recommendations about the treatment of osteoporosis or of vitamin deficiency. We're making recommendations that apply to generally healthy women who are seeking to supplement their diets to prevent fractures."
The public comment period for the new draft recommendations runs through July 10.
The recommendations were based on reviews of 16 studies, including the Women's Health Initiative, in which participants took supplements of vitamin D and calcium in varying combinations and amounts.
"Many women are taking higher doses of vitamin D already, and that is where there is not sufficient evidence for us to make a recommendation one way or another," Bibbins-Domingo said.
published recently in the Endocrine Society's Journal of Clinical Endocrinology and Metabolism
suggests, meanwhile, that vitamin D, when taken with calcium, can reduce the rate of mortality in older people.
In the review of previous studies, which assessed mortality among patients randomized to either vitamin D alone or vitamin D with calcium, the authors suggest that any beneficial effect went beyond reduced fracture risks.
"This is the largest study ever performed on effects of calcium and vitamin D on mortality," said
, PhD, of Aarhus University Hospital in Denmark, and lead author of the study which looked at more than 70,000 patients. "Our results showed reduced mortality in elderly patients using vitamin D supplements in combination with calcium, but these results were not found in patients on vitamin D alone."
For the study, researchers used pooled data from eight randomized controlled trials with more than 1,000 participants each. The patient data set was comprised of nearly 90% women, with a median age of 70 years. During the 3-year study, death rates were 9% lower in those treated with vitamin D with calcium.
"Some studies have suggested calcium (with or without vitamin D) supplements can have adverse effects on cardiovascular health," said Rejnmark. "Although our study does not rule out such effects, we found that calcium with vitamin D supplementation to elderly participants is overall not harmful to survival, and may have beneficial effects on general health."