J. D. Wark1, L. M. Paton*1, T. J. Beck2, C. Nowson*3, M. Cameron*1, S. Kantor*1, H. A. McKay4, M. Forwood5. 1Medicine, University of Melbourne, Parkville, Australia, 2Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA, 3School of Health Sciences, Deakin University, Burwood, Australia, 4School of Human Kinetics, University of British Columbia, Vancouver, BC, Canada, 5Anatomy and Developmental Biology, University of Queensland, Brisbane, Australia.
A high dietary calcium intake is widely recommended for children to enhance peak bone mass but the effect of calcium on the biomechanical properties of the proximal femur is not widely reported. We conducted a randomized, placebo-controlled trial of calcium supplementation (1000 – 1200mg daily) in 79 pairs of female twins aged (mean (SD)) 12.2 (2.0) years at baseline, using a powerful co-twin control design. Bone properties were able to be evaluated by Hip Structural Analysis (HSA) of proximal femur densitometry scans in 64 twin pairs (34 monozygotic, 30 dizygotic) up to 18 months intervention. HSA parameters were measured at the narrowest segment of the femoral neck (NN), intertrochanteric (IT) and upper femoral shaft (FS) sites. All data were adjusted for age, height and weight, none of which differed between groups at any time point. After 18 months at the IT and FS sites, there were significant within- pair differences in percent change from baseline comparing calcium – placebo treated twins, respectively: at the IT site, in areal bone mineral density (ABMD) [2.0 %, p = 0.04] and the average buckling ratio [-4.2 %, p = 0.002], respectively; at the FS site in ABMD [2.7 %, p = 0.01], endocortical diameter [-3.1%, p = 0.02], average cortical thickness [3.4%, p = 0.01] and average bucking ratio [4.7%, p = 0.009], respectively. At 6 months there was a difference in NN subperiosteal width and endocortical diameter but this was not maintained. Therefore, observed effects were limited to the IT and FS sites. At the femoral shaft there was inhibition of modelling at both endosteal and periosteal surfaces, resulting in narrowing of the femoral shaft and a thicker cortex. The implications for adult bone health are uncertain since the effects were more evident at the shaft site rather than the more proximal sites where osteoporotic fractures are common. Our findings complement the sparse body of literature that, importantly, investigates the geometric adaptation of growing bone to lifestyle factors. It is possible that calcium given during growth may reduce bone fragility in later life through an increase in cortical thickness.