More Vitamin D Studies Would Be 'Futile,' Researchers Say

Article excerpt

A new meta-analysis has found that taking vitamin D supplements offers no protection against heart attack, stroke, cancer and fractures in otherwise healthy people.

The only people found to benefit from the supplements were elderly women living in nursing homes or other residential care facilities. In that group -- and that group alone -- supplements of vitamin D and calcium were associated with a reduced risk of hip fractures.

This finding, which was published online Friday in the journal Lancet Diabetes & Endocrinology, shouldn't come as a surprise. Late last year, another meta-analysis also reported that a high intake of vitamin D failed to prevent illness. That study's list of illnesses not helped by the supplement was even longer. It included, for example, acute respiratory infections (like the common cold and the flu), diabetes, multiple sclerosis, rheumatoid arthritis, dementia, depression and Parkinson's disease.

The authors of the new meta-analysis -- a team led by Mark Bolland, a senior research fellow at the University of Auckland in New Zealand -- went one step further, however. Using a mathematical model known as a trial sequential analysis ("futility analysis"), they determined that future clinical trials involving vitamin D supplementation would be unlikely to alter the findings of existing studies by 15 percent or more (a "futility threshold").

In other words, any future clinical trials on the effects of vitamin D supplementation would be pointless.

"In view of our findings, there is little justification for prescribing vitamin D supplements to prevent myocardial infarction [heart attack] or ischaemic heart disease, stroke or cerebrovascular disease, cancer, or fractures, or to reduce the risk of death in unselected community-dwelling individuals," wrote Bolland and his colleagues. "Investigators and funding bodies should consider the probable futility of undertaking similar trials of vitamin D to investigate any of these endpoints."

A steady stream of studies

Yet those studies keep coming. As MedPage Today reporter Kristina Fiore pointed out last week in her "Vitamin D Blog," we're "only a month into 2014 and already PubMed lists nearly 70 new studies on vitamin D."

Press releases about vitamin D studies pop up in my inbox at least once or twice a week. The vast majority of them are observational studies that profess to show an association between low vitamin D levels in the blood and an increased risk of this or that disease.

But observational studies cannot prove cause-and-effect. For that evidence, randomized control trials are needed. And those trials, as the new meta-analysis points out, have found no support for supplementation as a preventer of disease. …