Healthy adults who take vitamin D supplements for osteoporosis prevention could spend their money more wisely on other healthcare needs, according to an article published online October 11 in the Lancet. The researchers contend that vitamin D supplements do not improve bone mineral density.
Ian R. Reid, MD, from the Faculty of Medical and Health Sciences, University of Auckland, New Zealand, and colleagues conducted a systematic review and meta-analysis of randomized controlled clinical trials in which the intervention was use of vitamin D supplements.
The researchers included 23 trials involving 4082 people, 92% of whom were women, with an average age of 59 years. In 19 of the trials, study populations were mainly white. The mean baseline serum concentration of 25-hydroxyvitamin D ranged from 16 (among Pakistanis living in Denmark) to 82 nmol/L, with the mean in 8 studies lower than 50 nmol/L.
Researchers in the trials measured bone mineral density at 1 to 5 body sites, including lumbar spine, femoral neck, total hip, trochanter, total body, or forearm. The supplement dose varied between studies, with 10 studies (n = 2294) using a daily dose of 800 IU or less.
The reviewers found that out of 70 statistical tests performed in the original studies, 6 tests showed significant benefit, 2 showed significant detriment, and the others showed no significant differences.
When Dr. Reid and colleagues performed a meta-analysis of the results, they found a small benefit at the femoral neck (weighted mean difference, 0.8%; 95% confidence interval, 0.2% - 1.4%) but no effect at other body sites. The meta-analysis also uncovered a bias toward positive results at the femoral neck and hip.
"Our data suggest that 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," the researchers write.
These new findings conflict with some reviews showing a benefit of vitamin D on fracture risk, the authors note. However, those reviews include studies in which the intervention is a combination of vitamin D and calcium, and fracture risk cannot be distinguished for vitamin D alone, they write. Research has shown that "vitamin D is not a compound mainly responsible for maintenance of bone calcium content, but rather for maintenance of circulating calcium concentrations, which are crucial for cardiac and neuronal function. Bone is merely a reservoir that can be drawn on for this purpose," the researchers write.
The new findings also contrast with the general perception that vitamin D works directly on bone cells, which is probably incorrect, the researchers add. Another recent clinical trend is to recommend high doses (more than 1000 IU) of vitamin D, although studies comparing high- and low-dose (400 - 800 IU) vitamin D suggest low dose is more beneficial, they conclude.
Dr. Reid and colleagues note that their findings are in agreement with the 2010 report from the Institute of Medicine. The authors of that report conclude that 40 nmol/L serum concentration was sufficient and that most American adults do not need supplements.
In an accompanying comment, Clifford J. Rosen, MD, from the Maine Medical Research Institute in Scarborough, writes, "Reid and colleagues' meta-analysis is consistent with our understanding of vitamin D: supplementation to prevent osteoporosis in healthy adults is not warranted. However, maintenance of vitamin D stores in the elderly combined with sufficient dietary calcium intake (800–1200 mg per day) remains an effective approach for prevention of hip fractures."
This research was funded by the Health Research Council of New Zealand. The authors and the commentator have disclosed no relevant financial relationships.
Lancet. Published online October 11, 2013. Article abstract, Comment extract
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