CHICAGO – Older adults who undergo Roux-en-Y gastric bypass are at risk for lessened bone mineral density for at least 2 years after their surgery and should be monitored appropriately for osteoporosis or fragility fractures, according to investigators from Massachusetts General Hospital in Boston.
Two years postoperatively, vertebral bone mineral density (BMD) in 30 patients was about 7% lower on quantitative computed tomography (QCT) and 6% lower on dual-energy x-ray absorptiometry (DXA) – both methods were used to ensure accuracy – when compared with 20 well-matched, morbidly obese controls. Total hip BMD was 6% lower on QCT and 10% lower on DXA. Femoral neck BMD was about 6% lower by both measures.
Biomarkers of bone turnover remained markedly elevated in surgery patients, as well, but unchanged in controls (C-telopeptide 0.65 ng/mL vs. 0.3 ng/mL; amino-terminal propeptide of type I collagen 65 ng/mL vs. 40 ng/mL). The findings were all statistically significant.
The groups started to separate early on BMD, and there’s concern that bone loss will continue for more than 2 years after surgery. Preoperatively, most Roux-en-Y gastric bypass patients have a higher than normal BMD, "so even a loss of 10% over 2 years is not going to put most of them in the osteopenic or osteoporotic range. The caveat now is that we are [offering surgery] to older patients and adolescents. Elderly patients are starting with lower bone mass, so there are concerns about [post-op] skeletal fragility. The oldest patient in our study was 72. She became osteoporotic after surgery because her bone density was low to begin with," said lead investigator Dr. Elaine W. Yu, an endocrinologist at Massachusetts General.
"In adolescents, there are implications for achieving peak bone mass. Even if you have a normal bone density 2 years after surgery, what’s going to happen in 10 years, 20 years?" she asked.
In short, "people should pay attention to bone density and bone loss and discuss this as one of the potential negative effects of bariatric surgery. For patients at risk, you should definitely consider serial bone density monitoring and osteoporosis therapy if needed," she said at the joint meeting of the International Society of Endocrinology and the Endocrine Society.
At baseline, both subjects and controls were about 47 years old and 270 pounds, with a mean a mean body mass index of 45 kg/m2. About 85% were women. The study excluded patients with histories of bone disorders or use of bone-affecting medications.
Surgery patients lost a mean of about 85 pounds in the first 6 months; their weight loss then stabilized, but they continued to lose bone. Controls stayed about the same weight.
The findings can’t be explained by post-op calcium or vitamin D depletion. "These subjects were aggressively supplemented with both," and both groups maintained normal levels throughout the study. Also, there were no statistical differences in parathyroid hormone levels between the groups.
"Our theory is that there are changes in gut hormones after gastric bypass that have direct effects on bone, like ghrelin," Dr. Yu said.
The National Institutes of Health funded the work. Dr. Yu is a consultant for Amgen.