Evidence is lacking for substantial health benefits of vitamin D, and results of several multimillion-dollar trials currently underway are unlikely to alter this view, according to a study.
The study, published Jan. 24 in The Lancet Diabetes & Endocrinology, examines existing evidence from 40 randomized controlled trials the gold standard for proving cause-and-effect and concludes that vitamin D supplementation does not reduce the risk of myocardial infarction, stroke, cancer or bone fractures in the general population by more than 15%. Thus, vitamin D supplements, which are taken by nearly half of U.S. adults, probably provide little if any health benefit, the researchers said.
Previous observational studies have shown that vitamin D deficiency is strongly associated with poor health and early death. However, evidence from randomized controlled trials indicates this association is not causal that is, that supplementation is not likely to have any benefit.
In line with this idea, the results of a large systematic review by Philippe Autier, MD, and colleagues, published in December in The Lancet Diabetes & Endocrinology, suggested that low levels of vitamin D are a consequence, not a cause, of ill health.
In the new study, Mark Bolland, PhD, of the University of Auckland, New Zealand, and colleagues build on this evidence using several types of meta-analysis, including a futility analysis, which predicts the potential of future study results to sway existing evidence.
The results of their study indicate the effect of vitamin D, taken with or without calcium, on MI, stroke, cancer and total fracture lies below a futility threshold. For hip fracture, the results of some trials even suggested increased risk with vitamin D supplementation. The authors analysis of whether vitamin D supplementation can reduce mortality by 5% or more was inconclusive.
In an accompanying commentary, Karl Michaëlsson, MD, PhD, of Uppsala University in Sweden, concludes: Without stringent indications i.e. supplementing those without true vitamin D insufficiency there is a legitimate fear that vitamin D supplementation might actually cause net harm.
Study abstract: www.thelancet.com/journals/landia/article/PIIS2213-8587%2813%2970212-2/fulltext