Vitamin D supplements are widely recommended to prevent bone fractures in older adults — but a clinical trial, published Wednesday in the New England Journal of Medicinefound that they may not do much after all.

In 2011, the National Academy of Medicine (then called the Institute of Medicine) recommended the general public get between 600 and 800 international units (IU) of vitamin D daily. That recommendation was based on past research showing that the vitamin may support bone health by aiding in calcium absorption and decreasing bone turnover, which causes bone deterioration.

Subsequent studies have yielded contradicting results; some concluded supplementing with vitamin D was beneficial, while one even found that high vitamin D levels caused by taking supplements could be harmful and cause more falls. Other trials have looked at both calcium and vitamin D together, making it difficult to analyze the vitamin’s effects on its own.

That was the goal of the new randomized clinical trial to determine whether adding vitamin D alone would preventatively improve bone health in men ages 50 and up and women ages 55 and up.

The results? For people who are healthy, “more is not better,” said lead study author Dr. Meryl S. LeBoff, director of the Skeletal Health and Osteoporosis Center at Brigham and Women’s Hospital in Boston.

The clinical trial included almost 26,000 adults who were followed for five years. Women made up half the number of participants, Black people comprised 20% and the median age was about 67 years. The vast majority had healthy vitamin D levels — just 2.4% had levels below 12 nanograms per milliliter, which is considered a severe deficiency. (The normal range for vitamin D is between 20 and 50 nanograms per milliliter, though LeBoff notes that these cutoffs are arbitrary and each individual is different).

To test if supplemental vitamin D would lower fracture risk — an important measure of bone health — the researchers compared the number of fractures that occurred over the five-year study period in people who took 2,000 IUs of supplemental vitamin D3 to the number of fractures in people who did not take the supplement. Vitamin D3 is a form of the vitamin that’s easier for the body to use; it’s produced naturally from sunlight or can come from animal sources. Another form of the vitamin, vitamin D2, is less easy for the body to absorb.

Even though the study didn’t look at the combined effects of vitamin D and calcium, the participants in the supplement group were allowed to take 1,200 milligrams of calcium per day, which is about the recommended daily amounts. This would allow them to get a healthy amount of the mineral, but avoid taking so much that it could have an effect on the results. (A key role vitamin D plays in the body is facilitating calcium absorption.)

In healthy people who were not severely deficient, supplementing with vitamin D did not seem to make any difference in protecting against fractures.

“The takeaway is that in general, people shouldn’t be popping vitamins left and right and if you’re trying to prevent fractures, vitamin D alone is not enough,” said Dr. Ethel Siris, an endocrinologist who works with osteoporosis patients at Columbia University Medical Center in New York. She was not involved with the trial.

According to Connie Weaver, a distinguished research professor of nutrition science at San Diego State University, most people get enough vitamin D from the sun and their diet — fortified milk and juice are common sources of dietary vitamin D in the US, and oily fish such as salmon and trout are naturally good sources of the vitamins. Supplements aren’t necessary for most people and don’t appear to provide additional bone benefits.

“In the context of reducing fractures, supplements won’t do much for most people,” Weaver, who was not involved with the new research, said.

LeBoff noted the findings do not apply to people who have severe vitamin D deficiency, low bone mass or osteoporosis. Supplements do make a difference in these cases — but even then, they don’t act alone.

According to Siris, people who are at high risk for fractures or are deficient do need extra doses of both vitamin D and calcium. People who have osteoporosis or low bone density may also need medications. In addition, exercise to strengthen bones is an important piece in preventing falls.

“Simply giving people vitamin D doesn’t prevent fractures,” she said. “But adequacy of calcium and vitamin D intake, in my opinion, remains a necessary part of the management of people with osteoporosis.”

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Judy Silverman contributed.