Vitamin D supplements do not increase bone strength or prevent bone fractures in children with vitamin D deficiency, according to a major new clinical trial.
The findings by Queen Mary University of London, UK, and the Harvard T.H. Chan School of Public Health, USA, challenge widely held perceptions relating to the effects of vitamin D on bone health, researchers say.
Although the potential for vitamin D supplements to improve bone strength has attracted growing interest in recent years, there have been no clinical trials designed to test if it can prevent bone fractures in children.
The research team worked with partners in Mongolia, which has a particularly high fracture burden and where vitamin D deficiency is highly prevalent, to determine if vitamin D supplementation would decrease risk of bone fractures or increase bone strength in schoolchildren.
The study, published in the latest edition of Lancet Diabetes & Endocrinology, is the largest randomised controlled trial of vitamin D supplementation to be conducted in children.
Over three years, 8,851 schoolchildren aged 6-13 living in Mongolia received a weekly oral dose of vitamin D supplementation.
Out of the total cohort, 95.5% had vitamin D deficiency at baseline and while the supplements effectively boosted vitamin D levels into the normal range, they had no effect on fracture risk or on bone strength. This was measured in a subset of 1,438 participants using quantitative ultrasound.
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 at the same time – 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 who were found to have rickets during screening for the trial were excluded from participation, as it would not have been ethical to offer them 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.”
Davaasambuu G, Polyna K, Uyanga B 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 1 December 2023
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