Weight loss surgery may cause bone loss

Patients continue to lose bone for at least two years after bariatric surgery, even after their weight stabilises, a new study has warned.
"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 Elaine Yu, the study's principal investigator and an endocrinologist at Massachusetts General Hospital, Boston.
"Therefore, bone health may need to be monitored in patients undergoing bariatric surgery," said Yu.
The standard imaging method for bone mineral density, dual-energy X-ray absorptiometry, or DXA, can sometimes give inaccurate results in obese individuals.
Therefore, researchers also measured bone density using a method that is often more accurate, a three-dimensional type of computed tomography (CT) called quantitative CT.

They compared bone density at the lower spine and the hip in 50 very 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, Yu said.
Two years later, bone density was 5 to 7 per cent lower at the spine and 7 to 10 per cent lower at the hip in the surgical group compared with the nonsurgical control group, as shown by both DXA and quantitative CT, Yu said.

She said the surgical patients had substantial and persistent increases in markers of bone resorption, the process of breaking down old bone that may play a role in bone loss.
The bone loss in the surgical patients, Yu said, occurred despite the fact that they were not losing any more weight in the 2nd year after surgery 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," she said.
The results were presented at the joint meeting of the International Society of Endocrinology and the Endocrine Society in Chicago.