To Örebro University

Objectives: Gastric bypass surgery constitutes the most common and effective bariatric surgery to treat obesity. Gastric bypass leads to bone oss but fracture risk following surgery has been insufficiently studied. Our objective was to investigate if gastric bypass surgery in obese patients, with and without diabetes, was associated with fracture risk, and if the fracture risk was associated with post-surgery weight loss or insufficient calcium and vitamin D supplementation.

Methods: Using large databases, 38 971 obese patients undergoing gastric bypass were identified, 7758 with diabetes and 31 213 without. Through multivariable 1:1 propensity score matching, well-balanced controls were identified. The risk of fracture and fall injury was investigated using Cox proportional hazards and flexible parameter models. Fracture risk according to weight loss and degree of calcium and vitamin D supplementation one year post-surgery was investigated.

Results: 77 942 patients had a median and total follow-up time of 3.1 (IQR 1.7-4.6) and 251 310 person-years, respectively. Gastric bypass was associated with increased risk of any fracture, in patients with diabetes and without diabetes using a multivariable Cox model (HR 1.26, 95%CI 1.05-1.53 and HR 1.32, 95%CI 1.18-1.47, respectively). The risk of fall injury without fracture was also increased after gastric bypass, both in patients with (HR 1.26 95%CI 1.04-1.52) and without diabetes (HR 1.24 95%CI 1.12-1.38). Weight loss or degree of calcium and vitamin D supplementation after gastric bypass were not associated with fracture risk.

Conclusions: Gastric bypass was associated with an increased risk of fracture and fall injury. Weight loss or calcium and vitamin D supplementation following surgery were not associated with fracture risk. These findings indicate that gastric bypass increases fracture risk, which could at least partly be due to increased susceptibility to falls.