Adequate calcium intake plus high physical activity may be useful for bone health in children
A meta-analysis by Winzenberg and colleagues (1) used areal bone
mineral density (BMD) to evaluate the effects of calcium supplementation
on the growing skeleton. However, bone material and structural properties
strongly affect its strength (2). A recent first prospective cohort study
including 6,213 children in southwest England showed that an increased
risk of fracture was associated with lower areal BMD (OR per SD decrease =
1.12), lower volumetric BMD (1.89) and smaller bone size relative to body
size (1.51) (3). Therefore, areal BMD would not be a good marker of
fracture risk in children; analysis using this marker could underestimate
the effects of calcium supplementation. The small positive effect of
calcium supplementation on upper limb areal BMD may result in significant
reduction of fracture risk in upper limbs, the most common fracture site
in children (4).
In addition, the positive effect on upper limb, but not hip or lumbar
spine, areal BMD (1) appears to suggest that adequate calcium intake is
required for bone gain at non-weight-bearing sites. Among 19 studies in
their meta-analysis (1), the trials by Iuliano-Burns et al, Stear et al,
Specker et al and Courteix et al found that calcium supplementation
supported the exercise-induced site-specific increase in areal BMD,
although subgroup analysis by level of physical activity showed no effect
modification (1). Bone strain from mechanical loads is an important factor
to control the skeleton, and bone mineralization in children is much lower
than that in adults. Thus, the lower material stiffness during growth
would accelerate load-induced bone gain and calcium incorporation into
bones could partly depend on their mechanical circumstances (5). In
children, high physical activity with appropriate calcium intake is a
candidate strategy for preventing fractures and it will be required to
determine the optimum amount of daily calcium intake dependent on physical
Toshihiro Sugiyama, M.D., Ph.D.
Department of Orthopaedic Surgery, Yamaguchi University School of
Medicine, Yamaguchi 755-8505, Japan; and Department of Veterinary Basic
Sciences, The Royal Veterinary College, University of London, London NW1
1. Winzenberg T, Shaw K, Fryer J, Jones G. Effects of calcium
supplementation on bone density in healthy children: meta-analysis of
randomized controlled trials. BMJ 2006;333:775-78.
2. Seeman E, Delmas PD. Bone quality: the material and structural
basis of bone strength and fragility. N Engl J Med 2006;354:2250-61.
3. Clark EM, Ness AR, Bishop NJ, Tobias JH. Association between bone
mass and fractures in children: a prospective cohort study. J Bone Miner
4. Cooper C, Dennison EM, Leufkens HGM, Bishop N, van Staa TP.
Epidemiology of childhood fractures in Britain: a study using the General
Practice Research Database. J Bone Miner Res 2004;19:1976-81.
5. Sugiyama T, Taguchi T, Kawai S. Adaptation of bone to mechanical
loads. Lancet 2002;359:1160.
Competing interests: No competing interests