Vitamin D supplements didn’t prevent kids’ broken bones, study finds

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Vitamin D supplements don’t prevent bone fractures in children, according to a recent analysis.

Vitamin D is naturally present in some fatty meats and fish oil and is produced when sunlight shines on human skin. It has been linked to bone health and plays a role in bone mineralization, which strengthens the skeleton.

To assess how vitamin D affects children’s fracture risk, researchers turned to a community of schoolchildren in Ulaanbaatar, Mongolia, where vitamin D deficiency and low calcium intake are widespread.

The study, published in the Lancet Diabetes & Endocrinology, looked at about 8,800 public schoolchildren ages 6 to 13 who did not already use vitamin D supplements. At the beginning of the study, 95.5 percent were vitamin D deficient. Half of the children received weekly vitamin D supplements of 14,000 IU, while the other half received a placebo.

When researchers followed up after three years, they found that those children who’d taken the supplements had higher vitamin D levels overall. But the group still experienced broken bones at the same rate as those who didn’t take the supplements. In fact, 6.4 percent of the kids who’d received vitamin D had broken one or more bones during the study period, compared with 6.1 percent of their counterparts. The effect didn’t differ substantially based on sex or calcium intake.

Although the Mongolian children’s fracture risk was “high,” and nearly double that of a group of nearly 200,000 Norwegian children in another study, the researchers said the fracture rate in their analysis lent more statistical power to the results. Nor did bone mineral density testing reveal significant differences among the children who took the vitamin and those who did not.

The supplements may have failed because they weren’t paired with calcium, which strengthens bones as well, researchers said.

“In adults, vitamin D supplementation works best for fracture prevention when calcium is given at the same time,” Ganmaa Davaasambuu, an associate professor in Harvard Medical School’s department of medicine and the study’s first author, said in a news release. “So the fact that we did not offer calcium alongside vitamin D to trial participants may explain the null findings from this study.”

The study also excluded children with rickets, a condition in which the bones soften because of vitamin deficiencies. Low-dose, daily vitamin D supplementation has been linked to rickets prevention, leading one 2021 study to declare that it is the “one condition above all others where there is conclusive and very longstanding evidence” of vitamin D supplements’ effectiveness.