Correlations between bone mineral density, insulin-like growth factor I and auxological variables

Recent studies have shown growth-related changes in spinal bone mineral density (BMD) in children; however, there is less information available on the relationship between BMD and insulin-like growth factor I (IGF-I). The aim of this study was to relate the BMD of the spine and radius with serum IGF-I levels and auxological variables in normally growing children. We used dual X-ray absorptiometry to measure the BMD in the lumbar spine (L1-L4) and distal radius of 121 children (69 boys, 52 girls) aged 3-18 years whose growth velocity was normal. Lumbar and radial BMD increased with age (p < 0.001) and puberty (p < 0.001) and was highly correlated to age, weight, height, body surface and bone age (r = 0.70-0.89 and p < 0.001 for all variables). Partial correlation, with age held constant, was weaker but still significant for most auxological variables. Serum IGF-I concentrations increased slowly during childhood and markedly during early stages of puberty, and correlated with lumbar and radial BMD (r = 0.55 and 0.45, respectively; p < 0.001) and with the auxological variables (p < 0.001). When age was held constant, IGF-I levels still correlated significantly with the auxological variables and with BMD, except in the case of radial BMD in boys. By multiple regression analysis IGF-I, unlike auxological variables, did not reach significance in the ability to predict BMD. Therefore, in healthy children, serum IGF-I levels show a weaker relationship to BMD than do auxological variables.