Gastric bypass is associated with reduced bone density, which may lead to osteoporosis and increased risk of fractures. Distal gastric bypass may increase the risk of bone loss even more due to malabsorption. We have previously shown an increased incidence of secondary hyperparathyroidism two years after distal gastric bypass as compared to standard gastric bypass. Whether these findings translate into increased risk of fractures remains unknown. Bone turnover markers are valid surrogate markers and may predict future osteoporosis and bone fractures. We compared bone turnover markers 2 years after surgery and correlation with s-PTH.
Patients with BMI 50-60 kg/m2 (n=113) were randomized to standard or distal gastric bypass. We measured fasting s-PINP (serum procollagen type I B propeptide) a marker of bone formation, and s-CTX (serum C-terminal telopeptide of type I collagen) a marker of bone resorption, s-PTH and s-ALP at baseline, 6 weeks, 6, 12, and 24 months after surgery. ANCOVA was used for comparing groups after surgery, adjusting for baseline differences, and multiple linear regression was run to investigate explanatory variables.
Two years after standard and distal gastric bypass mean (SD) s-PINP was 77.6 (24.2) and 80.0 (30.0) microg/l, respectively (p=0.39). Mean s-CTX was 0.79 (0.32) microg/l and 0.87 (0.37) microg/l, respectively (p=0.05). Both markers increased significantly from baseline in both groups (p<0.01, and p<0.01). Increased s-CTX correlated highly with s-PINP (Pearson r=0.62, p<0.001). S-CTX and s-PINP correlated independantly with s-PTH. Type of surgery did not independantly correlate with bone turnover markers.
Both s-CTX and s-PINP increased after standard and distal gastric bypass, and correlated with s-PTH. S-PTH increased significantly after distal gastric bypass compared to standard gastric bypass. Long-term prospective studies may define whether bone turnover markers or s- PTH predict future risk of osteoporosis and fractures after gastric bypass.