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July 27 (UPI) -- Vitamin D supplements, though widely recommended for bone health, don't lower the risk of fractures in healthy older adults, a large study has found. The analysis was prompted by inconsistent data on whether vitamin D supplements reduce broken bones in the general population, researchers at Brigham and Women's Hospital, an affiliate of Harvard Medical School in Boston, said in a news release.
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Their new study was published Wednesday in the New England Journal of Medicine.
The researchers found that, compared to a placebo, supplemental vitamin D3 of 2,000 international units per day did not reduce total, non-vertebral or hip fractures, according to the study.
Their analysis also showed no effects from supplemental vitamin D3 on major osteoporotic, wrist or pelvic fractures -- and no differences in the response to these supplements by men and women.
The results also didn't suggest any differences in the effects of supplemental vitamin D on fracture outcomes according to race or ethnic group, body mass index or age.
Men participating in the study were 50 years and older; women were 55 and older.
"Overall, the results from this large clinical trial do not support the use of vitamin D supplements to reduce fractures in generally healthy U.S. men and women," Dr. Meryl LeBoff, the study's lead author, said in the release.
However, the findings "do not apply to patients with severe vitamin D deficiency or low bone mass and osteoporosis or older adults in residential communities,"LeBoff, chief of the Brigham endocrine division's calcium and bone section, told UPI in an email.
She described the results as "a little surprising" since the investigators hypothesized that supplemental vitamin D actually would reduce total, non-spine and hip fractures.
However, she said, conflicting findings from previous randomized controlled studies "showed supplemental vitamin D resulted in a benefit, no effect or even harm on fracture risk."
To test their own hypothesis, the researchers carried out a large randomized controlled trial as an ancillary study to the VITamin D and OmegA-3 Trial. Known as VITAL, this is a national clinical trial of 25,000-plus men and women also led by investigators from Brigham and Women's.
VITAL has been exploring whether taking daily dietary supplements of vitamin D3 (2000 IU), omega-3 fatty acids or both lowers the risk of developing cancer, heart disease and stroke in people without a prior history of these illnesses.
From VITAL's large pool, the researchers confirmed 1,991 incident fractures in 1,551 participants over a median follow-up period of 5.3 years.
According to LeBoff, most study participants were not found to be deficient in vitamin D and already may have reached the vitamin D level needed for bone health.
The National Institutes of Health's Office of Dietary Supplements says most people meet at least some of their vitamin D needs through exposure to sunlight, but they consume less-than-recommended amounts of vitamin D.
Nationwide, an estimated 53.6 million individuals have osteoporosis, low bone mass or both, according to the study's paper. Two million osteoporotic fractures occur annually, and that number is expected to top 3 million fractures per year by 2040.
Osteoporosis, and ensuing bone fragility, is most often associated with inadequate calcium intake, NIH says, but insufficient vitamin D intake contributes to the condition by reducing calcium absorption.
On the other hand, NIH broadly warns that too much vitamin D from foods, beverages and dietary supplements may be harmful to health and suggests daily upper limits.
The investigators acknowledged their study's limitations, including the fact that they evaluated only one vitamin D dose and that the trial wasn't designed to test the effects of such supplementation in people who are vitamin D deficient.
LeBoff said the Brigham researchers' ongoing studies are "focusing on whether free vitamin D levels that we are measuring, or differences in genetic variation in vitamin D absorption, or metabolism and other factors may identify individuals" who may benefit from vitamin D supplements for musculoskeletal health.
