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Americans love a quick health fix in pill form: something to protect against illness, with minimal effort. For years, one of the go-to supplements has been vitamin D, thought to do everything from preventing cancer to strengthening bones.
Some bad news: Yet another big study adds to the pile of evidence that it’s useless for most people.
The new research, published on June 19 in JAMA Cardiology, combined the results of 21 randomized clinical trials to look at whether vitamin D supplementation was associated with a reduced risk of cardiovascular events, such as heart attacks or strokes.
The findings — based on studies involving 83,000 patients — were pretty bleak: Vitamin D supplementation was not associated with any cardiovascular benefit.
The new research follows a major meta-study, published in the Lancet, which looked at 81 randomized trials on whether vitamin D prevents fractures and falls and improves bone mineral density in adults. It found no benefit to musculoskeletal health.
“Something like 40 percent of older adults in the US take vitamin D supplements because they think it’s going to prevent against fractures and falls or cancer,” said Alison Avenell, the clinical chair of health services research at the University of Aberdeen and an author of the Lancet study, “and we’re saying the supplements for fractures and falls aren’t going to do that.”
These papers also build on previous meta-studies and the large-scale randomized trials that have shown the fat-soluble hormone doesn’t prevent fractures and may not have a role in preventing cancer or type-2 diabetes, but can increase the risk of kidney stones when taken along with calcium.
“There really is no health boost for vitamin D supplementation,” Clifford J. Rosen of the Maine Medical Center Research Institute in Scarborough, told Vox.
Of course, there are some cases when supplementation can be helpful: During pregnancy, for example, or for people who have been diagnosed with health conditions that may lead to vitamin deficiencies, like liver disease or multiple sclerosis. People with asthma, those who don’t get into the sun at all (like the homebound or institutionalized), or those from ethnic backgrounds with darker skin — African, Afro-Caribbean, and South Asian — may also benefit from a supplement.
But in most people with no symptoms of deficiency, the tablet shows such little utility that doctors are even questioning why we bother to measure vitamin D levels in those who aren’t at risk. Most of us actually get enough vitamin D without even trying.
So why all the hype about vitamin D?
The hype about the vitamin during the past two decades started with early vitamin D science. Before researchers run randomized controlled trials, they often look for links between health outcomes and exposures in large-scale population research called observational studies. And early observational research on the benefits of vitamin D uncovered associations between higher levels of vitamin D intake and a range of health benefits.
But the studies could only tell about correlations between vitamin D exposure and disease outcomes, not whether one caused the other. Still, they were enough to fuel media hype. Dr. Oz called the supplement “the No. 1 thing you need more of.” And the vitamin D industry helped create a craze by paying prominent doctors to expound on the benefits of testing and supplementation for everyone.
More recent randomized trials — that introduce vitamin D to one group and compare that group with a control group — have shown little or unclear benefit for both vitamin D testing and supplementation in the general population. And reviews that take these trials together to come to more fully supported conclusions, like the Lancet paper, are similarly lackluster.
In 2010, the Institute of Medicine (now known as the National Academy of Medicine) brought together an expert committee to review the evidence on the vitamin and figure out whether there was a widespread deficiency problem in North America. According to the 14-member panel, 97.5 percent of the population got an adequate amount of vitamin D from diet and the sun. (Vitamin D occurs naturally in fatty fish such as salmon and tuna, beef liver, cheese, and egg yolks. It’s also found in fortified foods such as milk, orange juice, and cereal.)
“You are at risk of D deficiency only if you have no sun exposure, live above 55 degrees latitude, and do not eat vitamin D-fortified foods or fluids [like milk],” said Chris Gallagher, a professor of Medicine at Creighton University, who wrote a comment about the Lancet paper. “About 80 to 90 percent of vitamin D comes from sunlight, and even 15 minutes in the midday will boost vitamin D levels to a good level.”
Still, testing and supplementation have exploded in the US. Over the past decade, the numbers of people using vitamin D supplements increased by a factor of four. Between 2000 and 2010, the amount Medicare spent on vitamin D testing rose 83-fold, making the test Medicare’s fifth most popular, after cholesterol.
These tests uncovered lots of low vitamin D levels — but there’s a scientific debate about how many of them are true deficiencies. Professional medical groups can’t agree on a cutoff. The Institute of Medicine recommended a diagnosis be made only for people who have less than 20 nanograms of the vitamin per milliliter of blood, but labs and other professional groups use higher thresholds. All that screening led to an explosion in diagnoses, and millions of Americans now pop daily vitamin D pills.
“The expectations were high, the results convincingly negative,” Rosen said of a recent New England Journal of Medicine study, which found vitamin D supplementation fails to prevent cancer and cardiovascular disease among older men and women. “Maybe people will stop taking vitamin D supplements, but somehow I doubt it. And certainly there is a strong case not to measure vitamin D in the blood in healthy individuals.”
