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Study finds vitamin D supplements don't prevent bone fractures in children

Vitamin D supplements don’t prevent bone fractures in children, according to a recent analysis of thousands of children in Mongolia, where vitamin D deficiency and low calcium intake are widespread.

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 mineralisation, which strengthens the skeleton.

The Washington Post reports that to assess how it affects children’s fracture risk, researchers turned to a community of schoolchildren in Ulaanbaatar, Mongolia, looking at about 8 800 children aged between six and 13 who were not on vitamin D supplements.

The study was published in The Lancet Diabetes & Endocrinology.

At the beginning of the study, 95.5% of the children were vitamin D deficient. Half of them received weekly vitamin D supplements of 14 000 IU, while the other half received a placebo.

In a follow-up after three years, the researchers 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% of of the kids who’d received vitamin D had broken one or more bones during the study period, compared with 6.1% 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 almost 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.

“In adults, vitamin D supplementation works best for fracture prevention when calcium is given at the same time,” said Ganmaa Davaasambuu, an associate professor in Harvard Medical School’s department of medicine and the study’s first author.

“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.

Study details

Vitamin D supplements for fracture prevention in schoolchildren in Mongolia: analysis of secondary outcomes from a multicentre, double-blind, randomised, placebo-controlled trial

Davaasambuu Ganmaa, Polyna Khudyakov, Adrian Martineau, et al.

Published in The Lancet Diabetes & Endocrinology on 1 December 2023


Vitamin D supplementation has been shown to increase total hip areal bone mineral density in healthy children and adolescents. We aimed to investigate whether supplementing schoolchildren living in Mongolia with weekly vitamin D3 for three years affected fracture risk.

We did a multicentre, double-blind, randomised, placebo-controlled trial across 18 public schools in Ulaanbaatar, Mongolia. Schoolchildren were eligible if they were aged 6–13 years at screening, had a negative QuantiFERON-TB Gold In-tube assay (QFT) result, were not hypersensitive to vitamin D or immunocompromised, did not use vitamin D supplements, did not have clinical signs of rickets, and had no intention of leaving Ulaanbaatar within 3 years. Participants were randomly assigned (1:1) to receive either vitamin D (oral dose of 14 000 international units [IU] vitamin D3, once per week) or placebo for 3 years using permuted block randomisation stratified by school of attendance. Participants, care providers, and all trial staff were masked to group assignment during the intervention. Prespecified secondary outcomes were incidence of fractures and adverse events, ascertained using questionnaires. The fracture and safety analyses included participants who completed at least one follow-up fracture questionnaire. We estimated adjusted risk ratios (RRs) and 95% CIs using generalised linear models with binomial distribution and a log link function with adjustment for school of attendance.

Between 2 September 2015, and 20 March 2017, 11 475 children were invited to participate in the study and 8851 were recruited and randomly assigned to receive either vitamin D (n=4418) or placebo (n=4433). 8348 participants were included in the fracture and safety analyses (4176 [94·5%] in the vitamin D group and 4172 [94·1%] in the placebo group). Of these, 4125 (49·4%) were female, 4223 (50·6%) were male, and 7701 (92·2%) were of Khalkh ancestry. Median age was 9·2 years (IQR 8·0–10·7) and 7975 (95·5%) participants had baseline serum 25-hydroxyvitamin D concentrations less than 50 nmol/L. During a median follow-up of 3·0 years (IQR 2·9–3·1), 268 (6·4%) participants in the vitamin D group and 253 (6·1%) in the placebo group reported one or more fractures (adjusted RR 1·10, 95% CI 0·93–1·29; p=0·27). Incidence of adverse events did not differ between study groups.

Oral vitamin D supplementation at a dose of 14 000 IU/week for three years was safe, but did not influence fracture risk in schoolchildren living in Mongolia who had a high baseline prevalence of vitamin D deficiency.


The Lancet article – Vitamin D supplements for fracture prevention in schoolchildren in Mongolia: analysis of secondary outcomes from a multicentre, double-blind, randomised, placebo-controlled trial (Open access)


The Washington Post article – Vitamin D supplements didn’t prevent kids’ broken bones, study finds (Restricted access)


See more from MedicalBrief archives:


Vitamin D supplements 'do nothing' to improve bone health


High prevalence of vitamin D deficiency in African populations


Double dose of vitamin D increases bone density in prem babies




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