Bone formation and resorption markers at 7 years of age: Relations with growth and bone mineralization

We aimed to describe bone formation and resorption markers in generally healthy prepubertal children using total alkaline phosphatase (tALP), osteocalcin (OC) and β-isomerized C-terminal telopeptides of type I collagen (β-CTx) serum concentrations and to estimate markers' correlations with anthropometric growth (height, weight, body mass index and trajectories of weight gain) as well as bone mineral content (BMC) and areal density (aBMD). We assessed 395 7-year-old children from the Generation XXI cohort with tALP, OC and β-CTx concentrations determined from a fasting venous blood sample and BMC/aBMD measured by dual-energy X-ray absorptiometry. Gender-specific reference intervals for tALP, OC and β-CTx in 7-year-old children were established by calculating the 2.5th and 97.5th percentiles. Pearson and partial correlation coefficients (controlling for sex, age, body size and season) between bone markers and growth measures were computed. tALP increased with height (rpartial controlled for sex = 0.26, 95%CI: 0.17, 0.35), was higher in overweight than in healthy weight children, and in children who gained weight above average during infancy. No correlations were found between OC or β-CTx and growth. In girls, OC was slightly correlated with subtotal BMC (rpartial = 0.22, 95%CI: 0.08, 0.35), subtotal aBMD (rpartial = 0.20, 95%CI: 0.06, 0.33) and lumbar spine aBMD (rpartial = 0.23, 95%CI: 0.09, 0.36). tALP and β-CTx were not correlated with any of the DXA-derived bone measures. This study contributed to the description of bone turnover at 7 years of age and suggested that bone metabolism markers measured in a single point in time have limited ability to describe anthropometric growth and overall bone status in generally healthy prepubertal children.