A Swedish study published in the Journal of Bone and Mineral Research indicates that the risk of a patient experiencing a fracture increases by about 30% after a gastric bypass operation. The surgery was associated with a higher fracture risk that appeared to increase with time and was not associated with the degree of weight loss or calcium and vitamin D supplementation.

38,971 patients who underwent gastric bypass operations were studied, of which 7,758 had diabetes and 31,213 did not. These patients were compared with an equally large group of individuals who had not been operated on and who had the equivalent morbidity and background data. Regardless of diabetes status, patients who had been operated on had about a 30% increased risk of fractures, said the researchers (Those without diabetes had an increased risk of 32% and those with diabetes had an increased risk of 26%.) The median follow?up time was 3.1 years

The risk increase applies to fractures in general, with the exception of the lower leg. The researchers said their results corresponded well with earlier research in the field, but highlighted that their study was statistically stronger due to its size.

They noted that the most common hypothesis of the mechanism behind increased fracture after obesity surgery had been weight loss and that the skeleton becomes weaker with the less load. The fractures of the lower legs however occurred less frequently. The study did not show a relationship between the fracture rate and the degree of weight loss. Larger weight loss or poor calcium and vitamin D supplementation after surgery were not associated with increased fracture risk.

Lead study author Kristian Axelsson, from the University of Gothenburg, said: “The fact that the risk of fractures increases and also seems to increase over time means that it will be important to follow patients, evaluate the fracture risk and, when required, institute measures to prevent fractures.”

Senior author Mattias Lorentzon, professor of geriatrics at the university, added: “Gastric bypass is a well-established method that has proven effective in reducing obesity, diabetes and mortality, so naturally our findings do not mean that you should stop providing these types of operations.”