Changes in Bone Metabolism After Gastric Bypass

Lawrence E Tabone, MD, Alexander Mor, MD, Anna Spagnoli, MD, Khoo Chin Meng, MD, Mike Muehlbauer, PhD, Alfonso Torquati, MD, MSCI. Duke University, University of North Carolina, National University of Health Systems Singapore.

INTRODUCTION – We hypothesize that metabolic operations increase bone metabolism. Our study objective was to determine the change in osteoclast activity and bone mineral density (BMD) one year after Roux-en-Y gastric bypass (RYGB) as compared to a control group.

METHODS AND PROCEDURES – Subjects were enrolled in a one year prospective longitudinal cohort study and were assigned to either surgical treatment with laparoscopic RYGB or medical management with diabetes support and education programs (DSE). All enrolled subjects had type II diabetes mellitus and morbid obesity (body mass index of 35 kg/m2 or greater). Dual-energy X-ray absorptiometry (DEXA) scans was performed at baseline and one year follow-up to determine change in BMD. Serums samples were collected at the same time points and analyzed using enzyme-linked immunosorbent assay for cross linked c-telopeptide of type I college (CTX), a marker of osteoclast activity. One year changes in BMD and serum CTX levels were compared within each group using a paired sample t-test.

RESULTS – One year after intervention subjects undergoing RYGB has a 280 percent increase in osteoclast activity as compared to a 7.6 percent increase in the DSE control group (p <0.001). A statistically significant decrease in bone mineral density in the left ribs (decrease of 6.8%, P < 0.05) and lumbar spine (decrease of 4.0%, P < 0.05) was seen one year after RYGB, which was not seen in the DSE group. The total bone mineral density was statistically unchanged within one year of intervention in both treatment groups.

CONCLUSION – There is a significant increase in osteoclast activity that is seen one year after RYGB along with a site specific decrease in lumbar spine BMD. Metabolic operations, like RYGB, increase bone metabolism. At one year after operation these changes are most evident with biochemical assessment and not by DEXA scan.

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