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Whether created from sunlight or taken in by food, vitamin D assists in the mineralizing and maintenance of bone. It is also thought to keep bones healthy as they age, prompting one in three adults aged 60 and older in the U.S. to take a vitamin D supplement and another third to take a multivitamin. Yet, it has long been unclear just how beneficial the vitamin is in preventing the bone fractures that many older adults dread as they age.

Now, a new study in the New England Journal of Medicine finally puts to rest the notion that vitamin D alone will help prevent bone fractures in the general adult population. From their large clinical trial dataset, researchers found daily doses of supplemental vitamin D did not significantly lower total bone fractures, nonvertebral fractures, or hip fractures. They found no differences in the effects of vitamin D on fractures based on race or ethnic group, body mass index, or age.

Meryl LeBoff, an endocrinologist, proposed the study to the Vitamin D and Omega-3 Trial (VITAL), a massive clinical effort based at the Brigham and Women’s Hospital, where LeBoff is the head of skeletal health and osteoporosis center, because it was an “an incredible opportunity to test hypotheses and science.”

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LeBoff said the study was “important for public health guidelines because of the overall scale, … duration and scope of the study, and the inclusion of men and women and … ethnic diversity.”

VITAL was constructed and led by JoAnn Manson, an epidemiologist and head of the prevention medicine division at Brigham and Women’s Hospital, to determine what benefit vitamin D had on the risk for cancer or cardiovascular disease in generally healthy men and women. In 2019, the VITAL group published findings that showed vitamin D supplements did not lower the risk of developing cancer or cardiovascular disease. The most recent study on bone fractures is just one of many ancillary studies of VITAL.

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“Vitamin D and calcium are essential for bone health,” Manson said. “But the key here is that it takes only small to moderate amounts of vitamin D to improve bone health to maintain bone health. And more is not necessarily better.”

VITAL veered from the common practice of focusing on patients with vitamin D deficiency, low bone mass, or osteoporosis to study the effect of vitamin D. Instead, it focused on the generally healthy midlife and older adult population. Manson said that decision was a product of conducting a randomized trial: “It would be unethical to identify people with vitamin D deficiency and then leave them untreated.” Participants were excluded from the study if they had a history of cancer, cardiovascular disease, or hypercalcemia.

The clinical trial’s impressive enrollment included 25,871 adults, 13,085 of whom were women, and 5,106 were Black. Participants were enrolled in all states in the U.S. Women were aged 55 years and older; men 50 years and older. Patients were either given vitamin D at a dose of 2,000 international units (IUs) or a placebo pill. The participants reported their incidents of bone fracture for a median of 5.3 years.

In the U.S., where an estimated 2 million adults suffer a fracture due to bone disease each year, and where more than half of people who experience a hip fracture in older age require assistance with daily living within one year, it’s not surprising patients and doctors turn to an easily accessible and cheap medicine like vitamin D to maintain bone health.

However, research has slowly chipped away at the previously unassailable perception of vitamin D providing older adults added benefits for bone health. As of 2018, the U.S. Preventive Services Task Force stated there was insufficient evidence to determine if vitamin D supplementation alone could prevent fractures in men and premenopausal women.

Steven Boyd, a biomedical engineer who lead a prior randomized clinical trial on high doses of vitamin D and bone health at the University of Calgary, said the results of the study were unsurprising and affirmed the emerging advice that adults “have to maintain a minimum level of vitamin D level and after that, you have a nice wide window where [the vitamin D level] is adequate.”

Yet, doctors continue to screen for vitamin D deficiency in patients, putting the vitamin D blood test at number 7 on the list of top lab tests based on Medicare spending.

Peggy Cawthon, scientific director of the Research Institute at California Pacific Medical Center, and co-author on the study, said the study “questions whether or not there’s too much screening for vitamin D deficiency and whether people without specific risk factors should be taking vitamin D supplements to improve their health.” Doctors and patients should look to osteoporosis medication or other interventions that increase bone density, Cawthon said.

Ian Reid, an endocrinologist at the University of Auckland, agrees, writing in an email to STAT: “The result of this study is not at all surprising…. It is high time that vitamin D supplementation of healthy adults was abandoned since it is a waste of money.”

However, Manson does not want the vitamin D pills tossed away. Many people will still benefit from vitamin D supplements, including those who cannot get sun exposure, eat vitamin-laden food, or have known bone health problems.

But for bone fracture prevention, Manson said vitamin D now has been shown to not provide clear benefits for the general adult population. Instead of supplements, perhaps doctors should prescribe outdoor exercise to patients wanting to strengthen bones and maintain a healthy level of vitamin D in the body, she said.

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