Millions of adults who collectively spend vast sums on vitamin D supplements to prevent osteoporosis would do well to save their money, according to a new study.
Despite vitamin D’s reputation as an essential nutrient for bone health, recent studies haven’t consistently shown that levels of the nutrient affect bone mineral density or that taking vitamin D supplements may prevent fractures. So researchers at the University of Auckland in New Zealand analyzed data from 23 randomized controlled trials that examined the effects of taking vitamin D supplements on bone mineral density, which is used to diagnose osteoporosis and predict fracture risk.
Their analysis, published online today in The Lancet, included 4082 healthy adults who took the supplements for an average of 2 years. The average age of participants in the studies was 59 years and 92% were women. In about half of the studies, participants took 800 IU or more of vitamin D daily.
The results showed that vitamin D supplements did not improve bone mineral density, with the exception of a small but significant increase at the femoral neck, the upper part of the thigh bone. However, the investigators said the increase likely wouldn’t aid in preventing fractures. “Most healthy adults do not need vitamin D supplements,” lead author Ian Reid, MD, said in a statement.
In fact, the investigators noted that research in recent years bucks the conventional wisdom that vitamin D works directly on bone cells to boost mineralization. Instead, they wrote that newer findings show vitamin D is more important for maintaining circulating calcium levels in the body than for sustaining the calcium content in bones.
In an accompanying editorial, Clifford Rosen, MD, of the Maine Medical Research Institute in Scarborough, said Reid and his colleagues’ analysis “is consistent with our understanding of vitamin D: supplementation to prevent osteoporosis in healthy adults is not warranted.” The exception, he added, is people with severe vitamin D deficiency, insufficient calcium levels, or both.
Reid and his coauthors noted that testing for vitamin D levels and taking supplements is costly. “The targeting of low-dose vitamin D supplements only to individuals who are likely to be deficient could free up substantial resources that could be better used elsewhere in health care,” they wrote.