A prospective longitudinal study of urinary excretion of a bone resorptionmarker in adolescents

In growing subjects, the rates of bone resorption and bone deposition are s ubstantially larger than in non-growing individuals. The purpose of this st udy was to measure the urinary excretion of a specific bone resorption mark er in function of adolescent growth stages in a prospective longitudinal st udy. A cohort of 60 adolescents (28 male and 32 female) was followed for 3. 4 years (range 1.7-4.6 years). Monthly measurements of height, weight and u rinary excretion of a bone resorption marker, collagen type I N-telopeptide s (NTx), were made. Changes in standing height were used to classify the ad olescents into one or more of six adolescent growth stages: pre-pubertal gr owth (continuous moderate growth rate), ascending growth spurt (increasing growth rate), peak growth spurt (growth rate higher than 7 cm/year for at l east 6 months), descending growth spurt (continuous decrease in growth rate ), end of growth (growth rate between 0 and 2 cm/year), and no growth. An i ncrease in NTx excretion from the pre pubertal to peak growth spurt of abou t 33% was found (44% and 27% for females and males respectively). The decre asing growth rate after the pubertal growth spurt coincided with a clear de crease in NTx excretion. These differences were statistically significant, except between the prepubertal and ascending growth stage. Individual mean NTx excretion during each growth stage was correlated with the individual's growth rate during that time (r = 0.81). There was large inter-and intra i ndividual variability. In non-growing adolescents (growth rate 0 cm/y) NTx excretion levels were 4-7 times greater than in adults. In all females, men arche was followed by a decrease in NTx excretion. In conclusion, the excre tion of a specific bone resorption marker, NTx, was correlated with the cha nges in growth rate during adolescence, both for males and females. There w ere large inter and intra-individual differences in NTx excretion during th e different growth stages. In adolescents who reached their adult height at the end of the pubertal growth spurt, bone resorption decreased dramatical ly but remained 4-7 fold higher than in adults.