CHICAGO — In one of the first studies to examine the long-term endocrine effects of gastric bypass surgery, it appears that after a loss in the first year post procedure, bone mineral density recovers in succeeding years, researchers reported at the annual meeting of the Society for Surgery of the Alimentary Tract.
Surgeons at Virginia Commonwealth University in Richmond prospectively collected data on 233 patients who were undergoing gastric bypass surgery. Of those, 82% had a Roux-en-Y procedure, 12% laparoscopically. The average age was 40 years, and the average body mass index was 50 kg/m
Dr. Johnson and his colleagues obtained preoperative bone mineral density (BMD) scans and found that most patients were normal at baseline, and remained at normal levels, even after surgery. Fifteen patients were osteopenic at baseline. Three developed osteopenia at 1 year post procedure. One patient with preoperative osteopenia actually had an increase in BMD after surgery.
At 1 year, for all patients, total forearm BMD decreased by 0.55%, and radius BMD increased by 1.85%. Total hip and lumbar spine BMD declined by 9.27% and 4.53%, respectively. These seem like fairly large decreases, but none of the patients developed osteoporosis during this period, Dr. Johnson said in an interview. The figures suggest a decline in the first year after gastric bypass, but the clinical significance of this is not yet known, he added.
At 2 years, forearm BMD decreased by 3.62%, but radius BMD remained steady. Both total hip and lumbar spine BMD recovered somewhat in the second year after bypass surgery, bringing them to almost the same levels as preoperatively.
At 3 and 4 years after surgery, BMD trended up, but there were too few patients at those time points to determine if the increases were statistically significant, Dr. Johnson said.
About 50%–60% of patients had calcium, parathyroid hormone, and vitamin D levels taken before surgery; all had those elements measured annually thereafter.
The mean serum calcium decreased from 9.8 mg/dL at baseline to 9.2 mg/dL in the first year, and to 8.8 mg/dL in the second year.
The parathyroid hormone level increased after surgery, which was not unexpected, Dr. Johnson said. It rose from 59.7 pg/mL preoperatively to 63.1 pg/mL in the first year, and to 64.7 pg/mL in the second year.
Vitamin D did not show any significant difference from preoperative level to 2 years, though it trended up. All the patients were given vitamin D postoperatively as part of a multivitamin supplement.
Dr. Johnson told attendees that at Virginia Commonwealth University, physicians recommend giving patients 1–1.5 grams of vitamin C and 400 IU of vitamin D daily, and monitoring them for BMD, calcium, parathyroid hormone, and vitamin D on an annual basis.
Although the study backed other reports showing an initial decline in BMD, the clinical significance is unclear, Dr. Johnson said. “We have shown it's not an ongoing process,” he added.