Someone holding a vitamin D supplement up to the sun.

A ccording to some reports, we’re in the middle of a “pandemic” of vita­min D deficiency, raising the risk of not just bone fractures but also heart disease, type 2 diabetes, depression, and more. And worries about these perils have led to an increase in vitamin D screening and supplement use: 31 percent of Americans ages 60 to 69, and 39 percent of those 70 and older, take high-dose (1,000 international units or more) vitamin D pills.

“Having low or deficient levels is not a part of normal aging, but it is very common,” says Audrey Chun, M.D., an associate professor of geriatrics and palliative medicine at the Icahn School of Medicine at Mount Sinai in New York City.

As people get older, she says, they tend to spend less time in the sun—which is what prompts the body to make vitamin D—and are less efficient at producing the nutrient.

Problem is, there’s a lot of confusion over the definition of deficient and whether you need more D than the daily recommended 600 IU (800 IU if you are older than 70). Recent studies have called into question the value of vitamin D supplements for most people.

Before you ask your doctor for a test or start popping pills, consider these facts.

The Evidence on Extra Vitamin D

“We know that people with low vitamin D levels are at risk for health problems, but the question is, if you treat the low vitamin D, can you prevent those issues?” says Erin Michos, M.D., an associate professor of medicine and epidemiology at the Johns Hopkins University School of Medicine. “And there haven’t been any trials showing this is the case.”

A review of 21 clinical trials involving 83,291 people with an average age of 66, published just last week in JAMA Cardiology, found that taking vitamin D supplements for at least one year didn't significantly reduce the risk of cardiac events such as heart attack and stroke, or death from any cause.

More on Vitamins

A key limitation: Few of the trials focused specifically on the effects of supplements on cardiovascular disease, but instead on issues such as bone density.

For this and other reasons, the researchers say that more studies on older adults, with a focus on heart-related conditions such as heart failure, would be "of interest." Still, they write, "The findings suggest that vitamin D may not confer cardiovascular protection and may not be indicated for this purpose." 

There's other recent research, too. An early 2019 study of more than 25,000 people 50 or older, published in the New England Journal of Medicine, found that taking 2,000 IU of vitamin D daily for five years failed to decrease the incidence of cancer or cardiovascular disease.

“Even those people who had low vitamin D levels to start with didn’t see a benefit,” Michos says.

When it comes to type 2 diabetes, the Vitamin D and Type 2 Diabetes (D2d) study, funded by the National Institutes of Health, recently found that high-dose supplements failed to offer significant protection to people at high risk for the condition.

In the study, whose results were published in mid-June in the New England Journal of Medicine, about half the 2,423 subjects took 4,000 IUs of vitamin D each day, while the rest took a placebo. All had prediabetes, and about 78 percent had sufficient blood levels of vitamin D at the start of the study.

The study subjects were followed for an average of two years to see whether the daily supplements would reduce the likelihood of full-blown diabetes by at least 25 percent. By the end, 24.2 percent of the people in the vitamin D group had type 2 diabetes, compared with 26.7 percent of those in the placebo group—a difference that was too small to be important, the researchers say. 

"Any benefit of vitamin D for diabetes prevention, if present, is modest and clearly does not pertain to a vitamin D-sufficient population," wrote Deborah Wexler, M.D., associate clinical chief of the Massachusetts General Hospital diabetes unit, an editorial in the same issue of NEJM. 

As for building bone and preventing fractures in older people, “a lot of people think the evidence is more robust than it is,” Michos says.

In a study of 379 adults 70 and older published in the American Journal of Clinical Nutrition in January, monthly doses of vitamin D (which averaged out to 400, 800, and 1,600 IU daily) failed to build bone mass or prevent falls. An analysis of 81 studies published in 2018 in the journal Lancet Diabetes & Endocrinology came to a similar conclusion.

“We didn’t find evidence that vitamin D prevented falls and fractures, but there were very few trials with people with ­really low vita­min D levels,” says Alison Avenell, M.D., clinical chair of health services research at the University of Aberdeen in Scotland and one of the study authors.  

Who Needs Screening?

Physicians use a blood test called 25(OH)D (25-­hydroxyvitamin D) to check vitamin D levels, but there’s no general consensus about what constitutes a “normal” level, according to the U.S. Preventive Services Task Force, which establishes recommendations about preventive health interventions and screenings.

A “low” from one lab could be an “ade­quate” from a different one.

Experts often rely on the National Academy of Medicine guidelines: Below 12 nanograms per milliliter is considered deficient; between 12 and 20 ng/mL is low. In the NEJM study, among those who had their vitamin D tested, just 13 percent fell below 20 ng/mL.

“We don’t recommend across-the-board vitamin D screening for older adults,” Chun says. People who are frail or in nursing homes should be checked. “It’s also reasonable to get screened if you’re a postmenopausal woman who might have osteopenia or osteoporosis. And men 75 or older should consider getting screened as well since they’re at risk of osteoporosis, too.” 

Where to Get Your Vitamin D

Sunlight on the skin—15 minutes during peak hours—triggers vitamin D synthesis. Vitamin D is also found in fortified milk, cereal, and orange juice; wild salmon; egg yolks; sardines; and canned tuna.

Most people can meet their vitamin D needs without a supplement, so there’s no reason to take one unless your doctor advises you to.

More vitamin D is not better, especially because excess amounts of the nutrient could increase the risk of kidney stones in some people. 

Editor’s Note: A version of this article also appeared in the April 2019 issue of Consumer Reports On Health.