Vitamin D and bone health in childrenBMJ 2011; 342 doi: http://dx.doi.org/10.1136/bmj.d192 (Published 25 January 2011) Cite this as: BMJ 2011;342:d192
- Nick Shaw, consultant paediatric endocrinologist
Osteoporotic fractures in adults are a substantial cause of morbidity and mortality, and they cost the health services about £2.3bn (€2.8bn; $3.6bn) a year in the United Kingdom and $30bn in the United States. Prevention, which includes manipulation of the development of bone mass during childhood and adolescence, is therefore important. Increasing peak bone mass in young adults might have a longstanding effect on the risk of osteoporosis in later years. Although genetic factors account for 50-85% of the variance in adult bone density, modification of environmental factors during childhood might have an effect on peak bone mass. One such factor is vitamin D⇓.
In a linked systematic review and meta-analysis (doi:10.1136/bmj.c7254), Winzenberg and colleagues assess the impact of vitamin D supplementation on bone density in children.1 They show that overall vitamin D supplementation had no significant effect on bone density in the whole body, hip, or forearm (with a trend to a small effect in the lumbar spine). However, in children with low serum vitamin D (defined as <35 nmol/L) supplements had a significant effect on whole body bone mineral content and borderline significance at the lumbar spine. The authors conclude that supplements are unlikely to be beneficial in children with normal vitamin D concentrations but could result in clinically useful improvements in children who are vitamin D deficient. The study complements previous research showing an association between vitamin D status and subsequent increments in bone density in peripubertal girls.2
What are the implications of this study for clinical practice and research given the high prevalence of vitamin D deficiency in children worldwide? Further research is important to clarify if such short term changes in bone density persist. The concept of peak bone mass influencing the risk of osteoporosis in adults has been a key influence on intervention studies in paediatric practice for many years but has recently been challenged.3 A systematic review of studies of calcium supplements in children showed that short term improvements in bone density were not maintained in the longer term.4 Most of the research to date has used dual energy x ray absorptiometry to assess bone density, and information about potential changes in bone geometry and estimated bone strength is limited. A recent randomised controlled trial in vitamin D deficient postmenarchal girls that used peripheral quantitative computed tomography in addition to dual energy x ray absorptiometry found that vitamin D supplements had no effect on bone density and geometry.5 Although bone density has been shown to be related to the risk of fracture in healthy children, fractures should be studied as an independent outcome in the short term in children with vitamin D deficiency and in the long term as adults.
What is the definition of vitamin D deficiency in clinical practice? This has been hotly debated given the current interest in the potential extraskeletal benefits of vitamin D. It has been recommended that serum concentrations of greater than 50 nmol/L or even 80 nmol/L should be regarded as vitamin D sufficiency.6 Many laboratories have adjusted their reference ranges for vitamin D to reflect such recommendations, with a consequent increase in the prevalence of abnormal results.
However, a recent UK consensus vitamin D position statement indicates there is currently no standard definition of an optimal concentration of vitamin D, and that concentrations below 25 nmol/L should indicate deficiency.7 Even at this value vitamin D deficiency is still prevalent in children worldwide. A study of adolescent girls in Beijing showed a 45% prevalence of vitamin D concentrations of less than 12.5 nmol/L during the winter.8 The National Diet and Nutrition Survey of 2008-9 has not yet published the results of vitamin D analysis, but it is likely to be similar to previous data showing that 20-34% of 2 year old Asian children in the UK had values under 25 nmol/L.9
The most immediate problem of vitamin D and bone health is rickets, which is the most prevalent bone disease in children worldwide. A resurgence of this disease has occurred in many developed countries, and the prevalence remains high in Asia, Africa, and the Middle East. Many countries are trying to tackle this by ensuring that vitamin D supplements are provided to vulnerable groups. Healthcare professionals need to ensure that these are readily available and being taken. Experience suggests that vitamin D supplementation involves logistical hurdles, and that sustained input is needed for this approach to translate into a reduction in the prevalence of rickets.10
The UK currently has no reference nutrient intake for vitamin D in children above the age of 4 years, in contrast to the rest of Europe and the US,11 because it is assumed that exposure to sunlight results in adequate concentrations of vitamin D.12 However, Winzenberg and colleagues’ review suggests that adequate vitamin D status is needed throughout childhood and adolescence. This is unlikely to be achieved by vitamin D supplementation alone, and advice on sensible sun exposure and more extensive food fortification needs to be considered.
Cite this as: BMJ 2011;342:d192
Competing interests: All authors have completed the Unified Competing Interest form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.
Provenance and peer review: Commissioned; not externally peer reviewed.