It may be time to pull the plug on future clinical trials examining whether vitamin D supplements prevent a variety of diseases, according to researchers at the University of Auckland in New Zealand.
The investigators analyzed findings from 40 randomized controlled trials aimed at determining whether vitamin D supplements, with or without calcium, may prevent heart attack, stroke, cancer, bone fractures, or death. Their study included a “futility analysis,” which determines whether the existing evidence is consistent and extensive enough to make additional research unnecessary.
In this case, the investigators calculated that current evidence would have to show the supplements reduced the risk of those diseases by at least 15% or decreased the risk of death by 5% or more to make further research worthwhile.
According to their results, published online today in The Lancet Diabetes & Endocrinology, vitamin D supplements, with or without calcium, did not meet the 15% threshold for heart attack, cancer, stroke, and bone fractures in the general public. However, findings showed that vitamin D with calcium may reduce hip fractures in elderly people living in nursing homes. Results on reducing the risk of death were inconclusive.
“The absence of findings in [a] large number of trials completed this far suggests that similar future trials will have a high chance of null or negative results and therefore might be viewed as a low priority by research funders,” the investigators wrote. Researchers and funding agencies alike should consider the “probable futility” of additional trials examining vitamin D’s effects on the diseases covered in their analysis, they added.
In an accompanying editorial, Karl Michaëlsson, MD, of the surgical sciences department at Uppsala University in Sweden, noted that recent US vitamin D supplement sales increased more than 10-fold, from $24 million in 2002 to $605 million in 2011.
Michaëlsson also noted ongoing uncertainties about the need for vitamin D supplements—varying recommendations on the blood level that constitutes insufficiency or deficiency and whether serum concentrations are directly linked with health outcomes. High-dose vitamin D supplements have been associated with an increased risk of fractures and falls, he added.
“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,” Michaëlsson wrote.