There is little justification for the use of vitamin D supplementation for the prevention of fractures or falls or for increasing bone density, according to the authors of a meta-analysis that found no benefits from supplementation.
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A systematic review and meta-analysis, published in the Oct. 4 edition of Lancet Diabetes & Endocrinology, examined 81 randomized controlled trials – involving 53,537 participants – of the effects of vitamin D supplementation on fractures, falls, or bone mineral density.
In the pooled analyses, researchers found that vitamin D supplementation did not reduce total fracture, hip fracture, or falls, even in trials in which participants took doses greater than 800 IU/day. Their results were similar when researchers compared high doses and low doses in their trials.
Similarly, vitamin D supplementation was not associated with any clinically relevant improvements in bone mineral density at any site; lumbar spine, total hip, femoral neck, forearm, or total body.
Even a post hoc analysis of randomized, controlled trials that compared daily high doses with daily low doses, as well as trials that compared intermittent high doses with intermittent low doses found no significant interactions for any outcome.
The paper also explored whether baseline vitamin D levels might influence outcomes. Eighteen trials in the analysis reported the results of subgroup analyses using baseline serum 25-hydroxyvitamin D (25[OH]D); three found no effects of vitamin D supplements in different subgroups of baseline, five studies found no effects of subgroups or interaction with baseline serum 25[OH]D, and one found mixed effects with respect to falls.
The outcomes for bone mineral density, as related to baseline serum 25[OH]D, were slightly more mixed. One trial found a positive effect of vitamin D supplements a bone mineral density for different subgroups of baseline serum, five trials reported mixed effects, and eight trials found no effects.
“The strengths of the current analyses are that they are comprehensive, include all available data from a large number of new trials, and concomitantly assess the major clinical and surrogate endpoints for musculoskeletal health,” wrote Mark J. Bolland, MD, of the department of medicine at the University of Auckland (New Zealand), and his coauthors. “Therefore, there is little justification for the use of vitamin D supplements to maintain or improve musculoskeletal health, and clinical guidelines should reflect these findings.”
They also conducted trial sequential analyses, which is a type of cumulative meta-analysis. For each outcome, they set a relative risk reduction threshold, then progressively reduced that threshold until the optimum sample size for that threshold exceeded the actual sample size.
“The trial sequential analyses are important because they provide estimates about the reliability of current evidence and the likelihood of future trials to change current conclusions,” the authors wrote.
Using this approach, they once again found clear evidence that vitamin D supplementation did not reduce fractures or falls for any measure of relative risk reduction. For hip fracture, the trial sequential analysis even found some uncertainty as to whether vitamin D supplementation might increase the risk of hip fractures.
Given the results of the trial sequential analyses, the authors argued that further similar trials were unlikely to alter their conclusion.
“If a large future trial has markedly different results to the current trials, adding its results will substantially increase the heterogeneity of the trial results, which in turn will reduce the weighting the new large trial receives in the pooled analyses,” they wrote. “Thus, adding a positive result from a large randomized, controlled trial will have only a small effect on the pooled result and is unlikely to alter the conclusions of these meta-analyses.”
They also noted that some of the studies had methodological limitations, and smaller studies of shorter duration tended to have “inflated” effect sizes, such that “the results of small, short-duration studies should be interpreted very cautiously, since they might not be replicated in larger, longer studies.”
The study was funded by the Health Research Council of New Zealand. Two authors declared grants from the Health Research Council during the study, one author is a shareholder in a company that provides bone mineral density measurements, and one reported grants from the Scottish Government Health and Social Care Directorates during the study.
SOURCE: Bolland M et al. Lancet Diabetes Endocrinol. 2018 Oct 4. doi. org/10.1016/S2213-8587(18)30265-1.