Patients who have had bariatric surgery continue to lose bone for at least two years, even after their weight stabilizes, according to study results presented at the 2014 joint meeting of the International Society of Endocrinology and the Endocrine Society. “The long-term consequences of this substantial bone loss are unclear, but it might put them at increased risk of fracture, or breaking a bone,” said lead study author Elaine Yu, MD, MSc, an endocrinologist at Massachusetts General Hospital in Boston and her research colleagues.
Dr. Yu’s team previously found that patients who have gastric bypass surgery lose bone mineral density within the first year after the surgery. Because the rate of bone loss was high, they researchers continued to monitor the patients in this study.
Since the standard imaging method for bone mineral density, dual-energy x-ray absorptiometry (DXA), can sometimes give inaccurate results in obese individuals, the investigators also measured bone density using quantitative computed tomography (QCT). They compared bone density at the lower spine and the hip in 50 obese adults (30 who had bariatric surgery and 20 who lost weight through nonsurgical ways but were similar to surgical patients in baseline age, sex, and body mass index). After surgery, nearly all patients received calcium and high-dose vitamin D supplementation.
Two years later, bone density was 5% to 7% lower at the spine and 7% to 10% lower at the hip in the surgical group compared with the nonsurgical control group, as shown by both DXA and QCT. In addition, the surgical patients had substantial and persistent increases in markers of bone resorption.
The bone loss in the surgical patients occurred despite the fact that the patients were not losing any more weight in the second post-surgical year and had stable blood levels of calcium and vitamin D. “Therefore, the cause of the bone loss is probably not related to weight loss itself,” Dr. Yu said.
None of the gastric bypass patients have required osteoporosis treatment, according to Dr. Yu. “The question is when is the bone loss going to stop? Over time this could be a problem in terms of fracture,” she said. Dr. Yu recommended that bariatric surgery candidates who have risk factors for osteoporosis receive bone density tests.