Gastric Bypass and Significant Surgically Induced Weight Loss Is Associated with Decreased Bone Mineral Density

Alex W Lois, BS, Matthew J Frelich, MS, Matthew I Goldblatt, MD, Nedra L Ohm, RN, Catherine R English, RN, James R Wallace, MD, PhD, Jon C Gould, MD. Department of Surgery, Division of General Surgery, Medical College of Wisconsin.

INTRODUCTION: Our objective was to examine the effect of laparoscopic Roux-en-Y gastric bypass (LRYGB) on patient’s bone mineral density (BMD). BMD is a useful metric for evaluating patients’ risk of developing osteoporosis and other bone related diseases. Bariatric surgical procedures such as the LRYGB that lead to weight loss through malabsorption may have a deleterious effect on BMD. We hypothesized that BMD would decrease at all examined locations following RYGB.

METHODS AND PROCEDURES: This study is a retrospective review of patients who underwent primary LRYGB at the Medical College of Wisconsin and received preoperative and postoperative bone density scans between January 2005 and November 2012. Bone density was evaluated with dual-energy X-ray absorptiometry (DXA) BMD scans. Routinely collected lab tests that might correlate with bone loss or nutritional status were also evaluated. Statistical analysis of our data was conducted using VassarStats (Vassar College, Poughkeepsie, NY). A correlational regression analysis was used to examine correlations between bone density change and continuous variables. Other continuous data were compared using two-tailed T-tests while Fischer’s exact test was used to compare categorical data. A p-value < 0.05 was considered statistically significant.

RESULTS: A total of 24 subjects met inclusion criteria for this study. All subjects were female with a mean age of 45.2 (±9.0) years. The mean interval between DXA BMD scans was 22.5 (±9.5) months. The mean % excess BMI lost (%EBL) for this series was 82.3% (±22.1). Hip and femur BMD % change correlated significantly with %EBL (p<0.01 and p=0.04, respectively).

 PreoperativePostoperativeMean % Changep-value
BMI (kg/m2)46.1 (±7.2)*22.7 (±9.6)*-82.3 (±22.1)*< 0.01
Bone Mineral Density (g/cm2)    
Spine1.31 (±0.13)1.24 (±0.14)-5.6 (±6.0)< 0.01
Hip1.16 (±0.14)1.05 (±0.14)-9.5 (±5.1)< 0.01
Femur Neck1.09 (±0.14)1.00 (±0.12)-8.4 (±4.7)< 0.01
Radius0.97 (±0.07)0.9 (±0.10)-7.1 (±5.6)< 0.01
Serum Levels    
Intact PTH47.6 (±23)47.7 (±18.4)8.1 (±40.6)0.98
Total Protein7.4 (±0.4)6.8 (±0.4)-7.2 (±5.8)< 0.01
Albumin4.2 (±0.3)4.1 (±0.2)-1.35 (±6.5)0.25
25-OH-Vitamin D22.9 (±10.7)39.8 (±12.1)105.2 (±107.2)< 0.01
Ca2+9.3 (±0.4)9.2 (±0.4)-1.0 (±3.8)0.21

Postoperative serum values collected 12 months (±6 weeks) following surgery. Postoperative BMI collected at nearest date to follow-up DXA BMD scan. BMD values are mean total of right and left sides when available. * Percent change is reported as %EBL.

CONCLUSIONS: Our results indicate that RYGB is associated with significant decreases in bone mineral density at all routinely examined locations in the years following surgery. Absorptive changes and changes in weight-dependent mechanical stress are possible mechanisms for the observed changes in bone density.

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