Researchers from Queen Mary University of London, UK, and Harvard T.H. Chan School of Public Health, US, have dispelled the longstanding myth that vitamin D supplements prevent fractures or improve bone strength in deficient children. The comprehensive study contradicts previous research findings that exaggerate the benefits of the vitamin on bone health.
While vitamin D supplements’ potential to improve children’s bone strength has garnered much interest due to its role in supporting bone mineralization, clinical trials have not been conducted before the current study to establish whether it prevents fractures.
“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,” explains Dr. Ganmaa Davaasambuu, associate professor at Harvard T.H. Chan School of Public Health.
Supplementation study
The study, published in Lancet Diabetes & Endocrinology is the largest randomized controlled trial of vitamin D supplementation conducted in children. It recruited 8,851 schoolchildren aged 6–13 in Mongolia with vitamin D deficiency at baseline. Of these, 4,125 were female, 4,223 were male and most of the sample population were of Khalkh ancestry.
The participants received a weekly dose of vitamin D supplements over three years. The supplements effectively boosted vitamin D levels to a normal level but did not affect fracture risk or bone strength. This was measured in a subset of 1,438 participants using quantitative ultrasound.
Mongolia has a high fracture burden and vitamin D deficiency is prevalent. The study sought to determine whether vitamin D supplementation would decrease the risk of bone fractures or increase bone strength in schoolchildren.
According to the researchers, approximately one-third of children have at least one fracture before the age of 18, which is seen as a significant global health issue because childhood fractures lead to disability and poor quality of life.
Reassessing bone health effects
To the researchers’ knowledge, the study was the largest randomized controlled trial conducted on children with vitamin D deficiency.
The researchers believe the trial findings will prompt scientists, doctors and public health specialists to reconsider the effects of vitamin D supplements on bone health.
Null results in the trial for outcomes relating to fracture incidence and bone strength were consistent with what was found in the researchers’ trial of schoolchildren in Cape Town, South Africa, and in trials with adults, which suggest that vitamin D does not reduce fracture risk in the absence of concomitant calcium supplementation.
In addition, no effect of vitamin D on fracture risk or radial SOS Z scores was seen in the subgroup of participants with higher calcium intake.
“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 a placebo,” says Adrian Martineau, lead at the Centre for Immunobiology of Queen Mary University of London.
“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 to prevent rickets should not be ignored. UK government guidance recommending a daily intake of 400 IU vitamin D remains important and should still be followed.”
Furthermore, researchers from the Vita-Salute San Raffaele University and IRCCS San Raffaele Hospital in Milan, Italy, found that Long COVID risk increases when vitamin D levels are low. The research was presented at the 25th European Congress of Endocrinology in Istanbul, Türkiye.
Meanwhile, another study published in the Annals of Internal Medicine found that adults with prediabetes who take vitamin D supplements are 15% less likely to develop diabetes.