A new study concludes that evidence is lacking for substantial health benefits of vitamin D – and that results of several multimillion-dollar trials currently underway are unlikely to alter this view.
The study, published in The Lancet Diabetes Endocrinology, examines existing evidence from 40 randomised controlled trials – the gold standard for proving cause and effect – and concludes that vitamin D supplementation does not prevent heart attack, stroke, cancer, or bone fractures in the general population by more than 15%. Thus, vitamin D supplements, which are taken by nearly half of US adults, probably provide little, if any, health benefit.Â
Previous observational studies have shown that vitamin D deficiency is strongly associated with poor health and early death. However, evidence from randomised controlled trials now indicates that 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 and colleagues, published in December 2013, also in The Lancet Diabetes Endocrinology, suggested that low levels of vitamin D are a consequence, not a cause, of ill health.Â