Bad news for pill poppers? Little clear evidence for Vitamin D efficacy, says Stanford's John Ioannidis

Vitamin D is a darling of the supplementation world. Deficiencies in the vitamin have been blamed for all manner of ailments, including diseases of the skeletal system, autoimmunity, infections and cancer.

Now researchers from the University of Edinburgh, Imperial College London and the University of Ioannina School of Medicine in Greece have analyzed 107 systematic literature reviews and 161 meta-analyses regarding vitamin D supplementation or levels in blood plasma and the occurrence of 137 various medical outcomes. They've published their findings in today's issue of the British Medical Journal, where they wrote:

In conclusion, although vitamin D has been extensively studied in relation to a range of outcomes and some indications exist that low plasma vitamin D concentrations might be linked to several diseases, firm universal conclusions about its benefits cannot be drawn.

In particular, the researchers found that the evidence does not support a role for vitamin D in increasing bone mineral density or reducing the risk of falls and fractures in older people. As senior author and Stanford study design expert John Ioannidis, MD, DSc, explained to me in an e-mail:

Vitamin D has been evaluated in thousands of studies in terms of its relationship to at least 137 health outcomes. We hope that systematic consideration of the available evidence will help avoid hot debate about health decisions involving vitamin D  that have mostly depended on speculations rather than evidence to-date.

Rather than writing off vitamin D altogether, the researchers note that additional, well-designed studies and trials are necessary before any firm conclusions can be drawn about its efficacy. The paper is accompanied by a second from researchers at the University of Cambridge analyzing relationships between vitamin D levels and the risk of mortality from several causes, as well as an editorial declaring that, despite much study, vitamin D is "no magic bullet."

Previously: The Lancet documents waste in research, proposes solutions, "US effect" leads to publication of biased research, says Stanford's John Ioannidis and Shaky evidence moves animal studies to humans, according to Stanford-led study
Photo by Colin Carmichael