The associations of obesity and other covariates with bone turnover markers in children and adolescents.

BACKGROUND: Procollagen type 1 N-terminal propeptide (P1NP) and C-terminal telopeptide of type 1 collagen (CTX) reflect skeletal metabolism during growth. We examined associations of obesity and other biological and behavioral factors with P1NP and CTX and assessed whether obesity-related associations varied by sex and across age groups approximating the pre-pubertal, pubertal, and post-pubertal periods. METHODS: Data were obtained from Canadian Health Measures Survey participants aged 6-20 years. Analyses included 3278 participants for P1NP (1658 males, 1620 females; 367 with obesity) and 1484 for CTX (762 males, 722 females; 162 with obesity). Survey-weighted multiple regression models were used to examine their associations with obesity status, physical activity, parathyroid hormone (PTH), serum 25-hydroxyvitamin D3 [25(OH)D3], and high-sensitivity C-reactive protein (hs-CRP), with all variables included simultaneously. Given the cross-sectional design, associations were interpreted as correlational. RESULTS: Overweight and obesity were associated with lower P1NP z-scores (β = -0.320 and - 0.378, both p < 0.001) and lower CTX z-scores (β = -0.378, p < 0.001; β = -0.278, p < 0.05). Obesity-status-by-age-group interactions were observed for P1NP and CTX (p < 0.001 and p = 0.002, respectively), whereas sex interactions were not significant. Obesity was not associated with lower marker levels in the age group approximating the pre-pubertal period but was associated with lower levels in age groups approximating the pubertal and post-pubertal periods. Cross-sectional age-related curves suggested that the highest estimated P1NP and CTX levels may occur at younger ages among participants with obesity, whereas marker levels were lower at older ages. High hs-CRP was associated with lower P1NP z-scores (β = -0.577, p < 0.001), while PTH was positively associated with P1NP and CTX z-scores (β = 0.117 and 0.103, both p < 0.01). Serum 25(OH)D3 status and physical activity were not significantly associated with either marker. CONCLUSIONS: Obesity-related differences in bone turnover varied across age groups, and the observed pattern may be broadly consistent with previously reported obesity-related differences in height velocity.