After combining data from 81 randomized controlled trials, researchers found no bone benefits from supplementing the vitamin, according to the report in The Lancet Diabetes & Endocrinology.
“Our results show that there is little reason for adults to take vitamin D supplements for their bones to protect against fractures, except people from high risk groups, such as those who have a prolonged lack of exposure to sunshine,” said study coauthor Dr. Alison Avenell of the University of Aberdeen in the UK.
Vitamin D supplements have long been recommended to seniors for treating and preventing the bone-thinning disease osteoporosis.
For the new study, Avenell and her colleagues scoured the medical literature for studies that examined the impact of vitamin D supplementation on bone health.
Ultimately they settled on 81 trials with a total of 53,537 participants. The length of time participants were studied varied widely, ranging from four weeks to as long as five years. More than three quarters of the trials included women over age 65.
Although most of the trials lasted a year or less.
“There were eight trials with over 33,000 participants that followed people up for three to five years. So the majority of the data comes from large, long-term trials.”
Most of the trials did not focus on participants with bone issues.
But, Avenell said, “one trial recruited people with low bone density, one with osteoporosis, six with people who had previous fractures – including one of the biggest with over 5,000 participants – 17 others were in older people from falls clinics, nursing homes or hospitals where increased risk of fracture was likely. Very few trials were in healthy younger populations.”
When the researchers pooled the data from all 81 trials, they found that vitamin D supplementation had no effect on the number of fractures and falls. Nor did the dosage of vitamin D seem to make any difference. Supplements also didn’t appear to increase bone density.
One big issue in studying vitamin D is there is no consensus on what’s a healthy level of the nutrient, Avenell said.
“The main reason older women begin to lose bone mass and to have fractures is loss of estrogen at menopause,” Siris said.
Siris said she’s concerned that news about the new research will convince people who already have brittle bones to stop taking their vitamin D supplements.