Serum markers of bone turnover are increased at six and 18 months after Roux-en-Y bariatric surgery: Correlation with the reduction in leptin

Abstract

Objective: The aim of the study was to examine serum markers of bone turnover at 6 and 18 months after Roux-en-Y gastric bypass surgery. Participants: Ten women and 10 men [body mass index (BMI), 50.2 ± 8.4 kg/m2] were studied at 6 months; 10 women and nine men (BMI, 47.2 ± 6.6 kg/m2) were studied at 18 months after surgery. Main Outcome Measures: Serum osteocalcin, bone specific alkaline phosphatase (BAP), N-telopeptide of type 1 collagen (NTX), PTH, 25-hydroxy vitamin D, and leptin were measured. Results: BMI was reduced 32.7 ± 6.2% at 6 months after surgery. Serum osteocalcin (6.9 ± 2.4 to 10.9 ± 2.6 ng/ml; P < 0.0001), BAP (14.2 ± 3.7 to 16.4 ± 4.5 ng/ml; P = 0.04), and NTX (10.9 ± 1.7 to 19.6 ± 5.3 nM bone collagen equivalents; P < 0.0001) were increased. Calcium, phosphate, and PTH were unchanged, but 25-hydroxy vitamin D increased (16.0 ± 8.9 vs. 26.9 ± 10.6 ng/ml; P <0.0001). The increase in NTX correlated with reduction in serum leptin (r = 0.58; P = 0.007). BMI was reduced 40.9 ± 7.5% at 18 months after surgery. Serum BAP (17.6 ± 5.3 to 22.2 ± 7.8 ng/ml; P = 0.0017) and NTX (10.8 ± 2.7 to 16.9 ± 5.5 nM bone collagen equivalents; P < 0.0001) were increased. Calcium, phosphate, and PTH were unchanged, but 25-hydroxy vitamin D increased (17.7 ± 7.6 to 25.6 ± 6.8 ng/ml; P < 0.0001). The increase in NTX correlated with reduction in BMI (r = 0.58; P = 0.009) and leptin (r = 0.45; P = 0.04) and the increase in serum 25-hydroxy vitamin D(r = 0.43; P = 0.05). In multiple regression (adjusted model R 2 0.263; P = 0.013), reduction in leptin was a significant predictor of increase in NTX (P = 0.016), but changes in BMI and 25-hydroxy vitamin D were not. Conclusions: Weight loss after bariatric surgery is associated with long-term increase in serum markers of bone turnover. The increase in NTX is related to the decrease in leptin, which may signal caloric restriction to the skeleton. Copyright © 2010 by The Endocrine Society.