Vitamin D doesn't protect against bone loss in older women, study finds

Vitamin D is no better than placebo for boosting bone mineral density, muscle function, and muscle mass, or reducing falls in postmenopausal women, according a study published August 3 in JAMA Internal Medicine.

“We did this study because there is a worldwide debate on the impact of vitamin D on musculoskeletal health. It’s all over the map. Some groups say you don’t need any vitamin D, while other groups say you need high dosages,” said lead author Karen Hansen, MD, MS, associate professor of medicine at the University of Wisconsin of School of Medicine and Public Health, in Madison, WI. “We found no data to support the need for high doses of vitamin D in postmenopausal women with baseline serum vitamin D levels around 20 ng/mL. We found that low and high doses had no impact on the bone and muscle outcomes compared to placebo.”

For this double-blind study, Dr. Hansen and colleagues recruited 230 postmenopausal (75 years or younger) women, between May 2010 until mid-2014, who had low vitamin D levels and no osteoporosis. They randomly assigned the women to one of three treatment groups: low-dose vitamin D (800 IU daily), high-dose vitamin D (50,000 IU twice monthly), or placebo.

After one year of therapy, the researchers measured subjects’ calcium absorption, bone-mineral density, muscle mass and function, and number of falls.

Results showed that calcium absorption increased 1% in the high-dose group, but decreased 2% in the low-dose group and 1.3% in the placebo group. Also, the high-dose vitamin D group achieved and maintained 25-hydroxyvitamin D levels at greater than or equal to 30 ng/mL.

But the small increase in calcium absorption in the high-dose group didn’t translate into beneficial effects, the authors found. The three treatment groups had no differences in measurements of bone density, strength, or muscle mass. Nor did the groups show any difference in numbers of falls, number of fallers, physical activity, or functional status.

“Our study shows that in postmenopausal women whose vitamin D levels are about 20 ng at baseline, pushing levels higher did not translate into clinical benefits,” Dr. Hansen said. “Instead, the study supports the Institute of Medicine conclusion that vitamin D repletion is a serum 25(OH)D level of ≥20 ng/mL.”

The researchers acknowledged that few African-American women participated in the study, which limits its ability to detect differential responses to vitamin D supplementation based on race. In addition, subjects participated for only 1 year, and perhaps longer exposure to high-dose vitamin D might yield greater effects on bone mineral density, the authors noted.

But for now, these results don’t justify the common and frequently touted practice of administering high-dose vitamin D, they concluded.

“Vitamins and supplements are always hot topics in science, and this study gives a more reasonable approach to vitamin D,” Dr. Hansen said. “Our health care dollars could be better spent on other preventive measures.”