Scientists find kids’ vitamin D supplements aren’t as effective as thought

Despite previous assumptions, taking vitamin D doesn’t help children avoid fracturing their bones.

Even if the child has a vitamin D deficiency, the supplements do not increase bone strength or prevent bone fractures, according to new research in the journal Lancet Diabetes & Endocrinology.

“The absence of any effect of sustained, generous vitamin D supplementation on fracture risk or bone strength in vitamin D-deficient children is striking,” Ganmaa Davaasambuu, associate professor at the Harvard T.H. Chan School of Public Health, said in a statement.

These findings go against the grain of widely held perceptions of how vitamin D helps bone health, the authors say in the paper. Vitamin D promotes the mineralization of bone, leading to the common belief that it can prevent bone fractures. However, until now, this had not been clinically tested. Childhood fractures can lead to disability and poor life quality, with around one-third of children having at least one fracture before they turn 18.

The authors tested whether taking vitamin D would decrease the risk of fractures in schoolchildren in Mongolia, where children often have bone fractures. They dosed 8,851 schoolchildren aged 6 to 13 with vitamin D every week for three years, 95.5 percent of whom had a vitamin D deficiency. After the trial, the children were found to have normal vitamin D levels, but had no change in their fracture risk, and no increased bone strength as tested using ultrasound. This marks the largest randomized controlled trial of vitamin D supplementation ever conducted in children.

“The study is very thorough in its design and execution although I don’t think that the use of ultrasound to assess ‘bone strength’ is a widely accepted methodology; speed of sound will reflect bone size and so vary progressively with age,” Nick Bishop, professor of pediatric bone disease, University of Sheffield, England, said in a statement.

The authors said that children with rickets were excluded as giving them placebo medication would have been cruel. Therefore, these findings are relevant only for those without rickets. The disease is a softening and weakening of bones caused by an extreme and prolonged vitamin D deficiency in children.

“In the U.K., fracture rates rise progressively through childhood, peaking when growth is most rapid in the teenage years,” Bishop said. “Children fracture when either they run into something, or something runs into them.

“We know from the ALSPAC study [the Avon Longitudinal Study of Parents and Children in Bristol, England] that lower bone size and mass for body size are associated with increased fracture risk, as is vigorous physical activity irrespective of bone mass; it is difficult to see how vitamin D supplementation would directly influence either of these factors in later childhood.

“Vitamin D supplementation during pregnancy, however, may be associated with increased body size-adjusted bone size and mass in childhood and routine vitamin D supplementation during pregnancy is something that might not only influence an infant’s risk of vitamin D deficiency and rickets, but also reduce their fracture risk as they grow and develop,” Bishop added.

This study therefore shows that, in Mongolia, vitamin D deficiency does not cause childhood fractures.

“Clearly, injuries and other factors are more relevant there. Unfortunately, in the U.K., we still see children suffering rickets due to Vitamin D deficiency,” Benjamin Jacobs, a consultant pediatrician, Royal National Orthopaedic Hospital in London, England, said in a statement.

“Indeed, we diagnosed a new case of rickets last week, so we must continue to improve the uptake of vitamin D supplements, and fortified foods, especially in the winter when we cannot make vitamin D from sunshine.

“As it says in the editorial, the focus really needs to be on preventing vitamin D deficiency rickets in early life, especially in low- and middle-income countries,” Jacobs added.

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