Natural history of bone metabolism and bone mineral density in children with inflammatory bowel disease

Background: In children with inflammatory bowel disease (IBD) it is not known whether reductions in bone mineral density (BMD) are a consequence of bone turnover alterations and if BMD improves with treatment. Methods: In a cohort of children with IBD, we prospectively measured indicators of bone remodeling, body mass index (BMI), disease activity, intact parathyroid hormone, serum IL-6, and insulin-like growth factor-I at diagnosis and then every 6 months for 2 years. BMD was determined annually using dual x-ray absorptiometry (DXA). BMD Z-scores were calculated using height/age. Baseline measurements and calcium intake were compared with a group of age- and sex-matched healthy children. Results: We observed that at diagnosis total body BMD Z-score (mean +/- SD) was -0.78 +/- 1.02 for Crohn's disease (CD, n = 58), -0.46 +/- 1.14 for ulcerative colitis (UC, n = 18), and -0.17 +/- 0.95 for control (CL, n = 49) (P < 0.01, CD versus CL). In CD, a BMD Z-score < -1.0 was associated with lower BMI and higher serum IL-6. Patients with CD and UC had low bone turnover. Activation of bone formation paralleled clinical improvement, but BMC gain was less than expected over the 2-year study period, especially in CD. Prednisone use did not correlate with low BMD. Conclusions: Decreased bone turnover occurs in children newly diagnosed with IBD. Although indicators of osteoblast activity increase with clinical improvement, bone mineral accrual does not accelerate. Children with low BMI may be considered for BMD screening, since they are at risk for low bone mass.