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Vitamin D supplements flopped for preventing fractures in low-risk adults over the age of 50, according to an ancillary study of the VITAL trial.

Over a median 5.3-year follow-up, participants taking 2,000 IU per day of supplemental vitamin D₃ did not see a significant effect on two site-specific fracture types, reported Meryl LeBoff, MD, of Brigham and Women's Hospital in Boston, and colleagues in the :

• Nonvertebral fractures: HR 0.97 (95% CI 0.87-1.07, P=0.50)
• Hip fractures: HR 1.01 (95% CI 0.70-1.47, P=0.96)

This was in addition to the previously reported topline findings that found no effect on total fracture risk (HR 0.98, 95% CI 0.89-1.08, P=0.70), which were presented at the 2021 American Society for Bone and Mineral Research annual meeting.

Looking at exploratory endpoints, there were no significant differences between groups for major osteoporotic fractures of the hip, wrist, humerus, or clinical spine (HR 0.99, 95% CI 0.83-1.17); pelvic fractures (HR 1.08, 95% CI 0.64-1.80); or wrist fractures (HR 0.89, 95% CI 0.69-1.15), excluding periprosthetic and pathologic fractures.

These findings were consistent even when taking into account a slew of baseline characteristics, such as BMI, serum 25-hydroxyvitamin D levels, age, sex, race, and ethnicity.

Notably, the study population consisted of generally healthy midlife and older adults, with no vitamin D deficiencies, low bone mass, or osteoporosis at baseline.

"Overall, the results from this large clinical trial do not support the use of vitamin D supplements to reduce fractures in generally healthy U.S. men and women," LeBoff explained in a statement. "Most participants in the trial were not deficient and may have already reached the vitamin D level needed for bone health."

Pointing out that over 10 million serum 25-hydroxyvitamin D tests are performed every year in the U.S. in their , Steven R. Cummings, MD, of the University of California San Francisco, and Clifford Rosen, MD, of Maine Medical Center Research Institute in Scarborough, said there is essentially "no justification" for these tests in the general patient population based on these findings.

"A 25-hydroxyvitamin D level might be a useful diagnostic test for some patients with conditions that may be due to or that may cause severe deficiency," they wrote. "For example, persons living in residential settings with little or no sunlight exposure or malabsorption or those receiving treatments for osteoporosis that might cause hypocalcemia may benefit from vitamin D supplementation; the need for measuring serum 25-hydroxyvitamin D levels in these groups remains uncertain."

Other than these unique scenarios, they suggested that "the use of the terms vitamin D 'insufficiency' and 'deficiency' should now be reconsidered."

While not necessarily effective at fracture prevention, vitamin D supplementation was safe and well-tolerated, without any major differences in hypercalcemia and kidney stone rates between the groups.

For this ancillary analysis of VITAL, LeBoff's group assessed outcomes among 25,871 adults (50.6% women, 20.2% Black) from all 50 states. All men were 50 and older, and all women were 55 and older. While calcium wasn't co-administered with daily vitamin D supplementation for most participants, there weren't any differences seen in the 20% who did take supplemental calcium up to 1,200 mg per day.

Fractures of the toe, finger, and skull, as well as periprosthetic and pathologic fractures, were excluded from the analysis.

"Our ongoing studies are focusing on whether free vitamin D levels or genetic variation in vitamin D absorption, metabolism, or receptor function will provide information about individuals who may benefit from supplemental vitamin D on musculoskeletal health," LeBoff said.

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