Most of Americans take vitamin D. Most should just stop

Outside of rare cases, rigorous studies of the supplement don’t find any health benefit.

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. Getty Images

By Julia Belluz, Vox

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 meta-study adds to the pile of evidence that it’s useless for most people.

The new research, published in Lancet Diabetes & Endocrinology, looked at 81 randomized trials on whether vitamin D prevents fractures and falls, and improves bone mineral density in adults. 

The findings of the review were unequivocal. “There is little justification for the use of vitamin D supplements to maintain or improve musculoskeletal health,” the authors wrote, except in rare cases when patients are at high risk of or being treated for rickets and osteomalacia.

“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 on the Lancet study, “and we’re saying the supplements for fractures and falls aren’t going to do that.” 

This new research builds 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, but can increase the risk of kidney stones when taken along with calcium. 

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 who don’t get into the sun at all, like the homebound or institutionalized, may also be prescribed a supplement. 

But for a health boost in people with no symptoms of deficiency, the tablet shows so little utility that doctors are even questioning why we bother measuring vitamin D levels in people who aren’t at risk of deficiency. 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 number one 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.

But 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 new 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 new 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. 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. All that screening also led to an explosion in vitamin D supplement use, and millions of Americans now pop daily vitamin D pills. 

When I asked Avenell what she thinks about the fact that so many people are diagnosed with deficiencies, she said, “It can’t be the case that just about the entire population is deficient in Vitamin D. It’s such an important nutrient, the body must have ways of making sure it doesn’t get short.”