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.
Supplement use has soared
Writing in a commentary that accompanies the meta-analysis, Dr. Karl Michaelsson, a professor of orthopedic surgery at Uppsala University in Sweden, points out how both the general public and health-care practitioners have in recent years become swept up in “the appealing idea” that taking vitamin D supplements prevents illness.
In fact, the last decade has seen the emergence of an entirely new medical diagnosis: vitamin D insufficiency.
As a result, “a massive demand now exists for the measurement of blood concentrations of 25-hydroxyvitamin D,” Michaelsson writes, and the supplemental use of vitamin D has soared. Americans spend more than $600 million on vitamin D supplements each year, up from $42 million in 2002.
But, as the new meta-analysis shows, there is no evidence that blood levels of 25-hydroxyvitamin D are related to health outcomes. Many researchers now believe that low blood levels of the vitamin are more likely a consequence than a cause of illness.
Furthermore, vitamin D blood tests are unreliable, says Michaelsson, for the results can be affected by a host of factors, including your genetic profile, what season it is, and how much body fat you have.
That hasn’t kept proponents of vitamin D supplementation from suggesting optimum blood concentrations of vitamin D, however. Those recommendations are all over the place, but, as Michaelsson points out, some of the recommendations would classify nearly everybody as having a vitamin D insufficiency.
Although Michaelsson doesn’t use the term, that development sounds like a classic case of “disease-mongering” — the widening of a diagnostic criteria in order to expand the market for treating a particular medical condition.
“Existing evidence does not lend support to the commonly held belief that vitamin D supplementation in general prevents osteoporosis, fractures, and non-skeletal diseases,” Michaelsson concludes. “Consequently, the impression that vitamin D is a sunshine vitamin and that increasing doses lead to improved health is far from clear.”
Other research suggests that taking vitamin D supplements when it’s not medically indicated may actually cause net harm, he adds. High doses of vitamin D have been found, for example, to actually increase the risk of fractures and falls.
“Until more information is available,” says Michaelsson, “it would be prudent to choose a cautious approach to vitamin D supplementation.”
You’ll find an abstract of the study at the Lancet Diabetes & Endocrinology website. Unfortunately, both the study and the commentary are behind paywalls.