SACRAMENTO, CA. - Vitamin D supplements, which are often combined with calcium supplements, are associated with a lower risk of bone fracture only when taken at high doses, a new study reports.
The study also helped shed light on why there have been conflicting reports about the benefits of Vitamin D.
Vitamin D has long been known to be essential for bone health, but research on supplements has been conflicting. Some studies have concluded vitamin D supplements can lower the risk of bone fractures, while others suggest the pills provide little to no benefit.
The latest study on the topic, published this week in the New England Journal of Medicine, may settle the questions on whether daily doses are effective for fighting bone loss and may help establish new guidelines for seniors.
Researchers re-analyzed data from 11 clinical trials comprising more than 31,000 people age 65 and older, found that Vitamin D is effective in high doses only.
Overall, 4% of the study participants fractured their hip during the studies, and 12% fractured a bone somewhere else in their body other than the vertebrae.
Taking less than about 800 international units (IU) of vitamin D per day, with or without calcium, had no effect on bone-fracture risk when compared with taking a placebo or a calcium supplement alone, the results indicated. Taking 800 IU or more, by contrast, decreased the risk of hip fracture by 30% and the risk of other bone fractures by 14%.
"A 30% reduction in hip fracture with an inexpensive and safe intervention such as vitamin D has enormous public health implications," says lead author Dr. Heike Bischoff-Ferrari, director of the Center on Aging and Mobility at the University of Zurich, in Switzerland.
The new findings go a long way toward explaining why past studies on vitamin D and fracture risk have produced conflicting results, says Dr. Robert P. Heaney, an osteoporosis researcher and professor of endocrinology at Creighton University, in Omaha, Nebraska.
"All of the problems with previous studies come from a very modest dose of vitamin D," says Heaney, who wrote an editorial that accompanies the study. "If you don't give [study participants] enough of the vitamin D, then you won't see an effect."
Should people over age 65 start taking at least 800 IU of vitamin D each day? Not necessarily. Although Bischoff-Ferrari and her colleagues suggest a daily supplement may be beneficial, other groups have stopped short of making the same recommendation.
The Institute of Medicine, an influential nonprofit organization, recommends that people in their 70s or older consume at least 800 IU of vitamin D per day. But that vitamin D can come from fortified foods - not to mention sunlight, which naturally spurs the body to produce the vitamin.
In June, the U.S. Preventive Services Task Force (USPSTF), a panel of independent experts that advises the federal government on preventive care, issued draft guidelines saying there is too little evidence to recommend vitamin D supplements for the prevention of bone fractures.
To complicate matters further, the dose needed to promote bone health appears to vary from person to person depending on his or her baseline vitamin D levels, Heaney says.
Bischoff-Ferrari says her team's analysis - "the best evidence we have today," she says - may merit a revision to the USPSTF recommendations, which have yet to be finalized and are open to public comment through July 12.
"I do think that our results can support a change in these recommendations for seniors," she says.