Once the ‘it’ supplement, vitamin D is losing its sparkle

The study randomly assigned thousands of men age 50 and older and women 55 and older to one of four groups to compare the impact of vitamin D, with or without fish oil, to placebo pills that contained neither.

Researchers found neither supplement had a significant effect in lowering the number of fractures in study participants.

“More is not necessarily better,” said Dr. JoAnn Manson, chief of preventive medicine at Brigham and Women’s Hospital and senior author of the study. “The findings suggest that you need only small to moderate amounts of D to maintain bone health.”

And that recommended amount, 600 to 800 daily International Units, or IU, for most adults, can easily be obtained through a healthy diet without supplements because the country’s food supply is heavily fortified with vitamins, Manson said.

Manson was among many scientists 12 years ago who held high hopes for the vitamin.

“I do think vitamin D is one of the most promising nutrients for prevention of cardiac disease and cancer, and I believe in it strongly,’’ she said in an 2010 Globe interview.

“But the evidence,” she said at that time, “is far from conclusive.’’

Subsequently, Manson and her team embarked on one of the country’s largest studies of vitamin D, known as the VITAL trial, which enrolled 25,871 men and women, and followed them for about five years to determine whether 2,000 IUs daily of vitamin D, or 1 gram of fish oil, reduced the risk of developing a long list of health problems in people who do not have a prior history of these illnesses.

The latest findings on bone fractures stem from the VITAL trial.

The body naturally produces vitamin D in response to the skin’s exposure to sunlight, and there have been concerns that darker-skinned individuals may be more at risk for fractures because their skin pigmentation reduces their ability to produce the vitamin. Some studies have linked low vitamin D levels to osteoporosis, a disease of weak, brittle bones.

But in the VITAL study, 20 percent of the participants were Black, and the researchers said their results did not suggest any differences in the effects of D supplements on fracture outcomes, regardless of race or ethnicity.

But there is a caveat. Cummings, Manson, and other doctors say the supplements may be needed for people living in settings with little or no sunlight exposure, such as nursing homes, or for those with conditions that hamper vitamin D absorption, such as Crohn’s or celiac disease, or those receiving treatments for osteoporosis.

Other studies and analyses have also found the supplements confer few benefits, including for mental health.

“It’s a little discouraging, but the foundation upon which vitamin D [daily recommended dose] was built on was a little shaky to begin with,” said Dr. Clifford Rosen, professor of medicine at Tufts University School of Medicine and an editor at The New England Journal of Medicine. He coauthored the recent journal editorial with Cummings about vitamin D’s demise.

Rosen also served on the Institute of Medicine panel that issued in 2011 the vitamin D guidance of 600 to 800 IU daily for most adults. But Rosen said that since then, he witnessed a mounting number of studies that revealed a lack of evidence for vitamin D preventing many major diseases.

Yet at the time the panel issued its guidance, he said, there was just one meta analysis of several studies that suggested 800 IUs were effective, and one study from 1992 reported that 1,200 milligrams of calcium, together with 800 IUs of D daily, reduced bone fractures in elderly women.

“There was not a lot of evidence or super controlled trials,” he said. “But that’s what everyone has used as the gold standard.”

Rosen said he has trouble convincing many of his patients and even his wife that they don’t need to be regularly screened for vitamin D deficiency.

At the same time, other physicians worry that patients who should be taking supplements will interpret the new findings as permission to toss out the nutrients.

“Should the average person take a supplement? The answer in this study is no,” said Dr. Michele Bellantoni, associate director of post-acute and long-term care at Johns Hopkins Bayview Medical Center. “But my worry is that my osteoporosis patients will stop taking their supplements.”

Osteoporosis patients often take medications that need vitamin D and calcium supplements to work properly, she said.

Bellantoni and other physicians said they have had many patients say they started taking vitamin D because they heard it may protect them from the most severe symptoms of COVID.

But two recent trials, including one from Rosen, found no benefit from vitamin D supplements for patients hospitalized with COVID.

Now, Manson, the Brigham and Women’s physician who led the landmark VITAL trials, is wrapping up a trial to determine whether higher doses of vitamin D for people with COVID might tamp down the body’s inflammatory response to infection and prevent hospitalization.

Many serious COVID complications occur when the infection triggers a person’s immune system to flood their body with proteins that damage organs.

Manson is basing her theory on findings from one of her studies that suggested vitamin D might reduce the risk for certain autoimmune diseases, such as rheumatoid arthritis, because the diseases are also characterized by inflammation.

She expects to report findings this fall.

While many of the VITAL studies have indicated vitamin D supplements for generally healthy adults do not reduce their risk for developing some common diseases, Manson said they also showed that taking up to 2,000 IUs a day was not harmful.

“I think we should spend a lot more time outdoors being physically active rather than popping a pill,” Manson said.

But that said, she is taking 1,000 IUs of D in a daily multisupplement. She does that, she said, “to hedge my bets.”

Kay Lazar can be reached at kay.lazar@globe.com Follow her on Twitter @GlobeKayLazar.