Vitamin D supplements do not increase bone strength in children

Challenging widely held perceptions.


Before the age of 18, about one-third of children and adolescents have at least one fracture, with the risk spiking around the time of the pubertal growth spurt. The effects can vary from brief activity restriction to hospitalization and, in rare cases, permanent impairment.

Because of the physiological function of vitamin D’s active metabolite, calcitriol, in promoting calcium absorption, vitamin D supplementation has garnered significant attention as a potential means of achieving this goal. Inconsistent results have been found in observational studies examining the relationships between low vitamin D status and an increased fracture risk.

A major clinical trial led by Queen Mary University of London and the Harvard T.H. Chan School of Public Health investigated whether supplementing schoolchildren living in Mongolia with weekly vitamin D3 for three years affected fracture risk. The study reveals that children with vitamin D deficiency do not benefit from vitamin D supplementation regarding stronger bones or prevention of bone fractures. The results refute commonly accepted beliefs about how vitamin D affects bone health.

This study is the largest randomized controlled trial of vitamin D supplementation ever conducted in children.

8,851 Mongolian schoolchildren, ages 6 to 13, received a weekly oral vitamin D supplement over three years. In the beginning, 95.5% of individuals had vitamin D deficiency. Supplementing with study supplements was a highly effective way to raise vitamin D levels into the normal range. Yet, when assessed by quantitative ultrasonography in a subset of 1,438 subjects, they had no impact on fracture risk or bone strength.

Scientists, physicians, and public health experts will probably reevaluate the impact of vitamin D supplementation on bone health in light of the trial results.

Dr Ganmaa Davaasambuu, Associate Professor at the Harvard T.H. Chan School of Public Health, said:

“The absence of any effect of sustained, generous vitamin D supplementation on fracture risk or bone strength in vitamin D deficient children is striking. In adults, vitamin D supplementation works best for fracture prevention when calcium is given simultaneously – so the fact that we did not offer calcium alongside vitamin D to trial participants may explain the null findings from this study.”

Professor Adrian Martineau, Lead of the Centre for Immunobiology at Queen Mary University of London, added:

“It is also important to note that children found to have rickets during screening for the trial were excluded from participation, as it would not have been ethical to offer them a placebo (dummy medication). Thus, our findings only have relevance for children with low vitamin D status who have not developed bone complications. The importance of adequate vitamin D intake for prevention of rickets should not be ignored, and UK government guidance recommending a daily intake of 400 IU vitamin D remains important and should still be followed.”

Journal Reference:

  1. Davaasambuu Ganmaa, Polyna Khudyakov, Uyanga Buyanjargal et al. Vitamin D supplements for fracture prevention in schoolchildren in Mongolia: analysis of secondary outcomes from a multicentre, double-blind, randomised, placebo-controlled trial. Lancet Diabetes & Endocrinology. DOI: 10.1016/S2213-8587(23)00317-0


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