Vitamin D Blog: Protection Is Futile

Only a month into 2014 and already PubMed lists nearly 70 new studies on vitamin D.

The weight of the evidence in terms of randomized controlled trials suggests that vitamin D doesn't offer protection against fracture, MI, ischemic heart disease, stroke, or cancer – and it's unlikely that future large trials will change those results, according to a meta-analysis published in the Lancet Diabetes & Endocrinology.

Mark Bolland, PhD, of the University of Auckland in New Zealand, and colleagues conducted a futility analysis of 40 randomized controlled trials of vitamin D. The futility analysis predicts the potential of a future study to sway the existing evidence, and the authors put that figure at a 15% risk reduction. If the meta-analysis returned results above that threshold, new trials could potentially tip the balance of the evidence.

But Bolland and colleagues found that the effect estimates for vitamin D supplementation (with or without calcium) for those musculoskeletal and vascular outcomes remained within the futility boundary – showing that vitamin D supplementation doesn't alter relative risk of any of these endpoints by 15% or more.

That suggests that several large, costly studies currently underway aren't likely to change the overall weight of the evidence, they said.

"Investigators and funding bodies should consider the probable futility of undertaking similar trials of vitamin D to investigate any of these endpoints," they wrote.

The study did suggest, however, that vitamin D plus calcium did appear to reduce hip fracture – but only in institutionalized patients, and the results were limited to two randomized trials. Also, they noted, it was unclear whether vitamin D had any impact on mortality.

In an accompanying editorial, Karl Michaelsson, MD, of Uppsala University in Sweden, acknowledged that the "body of evidence is already sufficiently large" and future studies may not change these pooled estimates.

"Existing evidence does not lend support to the commonly held belief that vitamin D supplementation in general prevents osteoporosis, fractures, and nonskeletal diseases," he wrote. "Consequently, the impression that vitamin D is a sunshine vitamin and that increasing doses lead to improved health is far from clear."

"Without stringent indications -- i.e. supplementing those without true insufficiency -- there is a legitimate fear that vitamin D supplementation might actually cause net harm," he concluded. "Until more information is available, it would be prudent to choose a cautious approach to vitamin D supplementation and to put more emphasis on the development of evidence-based cutoff points for vitamin D inadequacy."

Source: www.medpagetoday.com