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Despite the benefits associated with long-term weight loss that are achievable with bariatric surgery, such procedures lead to abnormal bone and mineral metabolism. In a prospective 1-year study, researchers evaluated bone metabolism and BMD in 23 morbidly obese men and women (mean BMI, 47 kg/m2) who underwent Roux-en-Y gastric bypass (RYGB) surgery, which is the most commonly performed bariatric surgery procedure. Following surgery, patients who were ≤50 were prescribed 1500 mg calcium citrate and 600 IU vitamin D daily; older patients were prescribed 1800 mg calcium citrate and 800 IU vitamin D daily. Eighteen participants were women, 7 of whom were postmenopausal.
Overall, mean weight loss was 45 kg during the first postoperative year, and mean BMI dropped to 31. At 12 months, mean BMD had declined by 9.2% at the femoral neck and 8.0% at the total hip, but mean BMD at the lumbar spine had not changed significantly. Degree of BMD attenuation correlated strongly with extent of weight loss. Despite supplementation of calcium and vitamin D intake, urinary calcium dropped, and serum hydroxylated vitamin D concentrations remained unchanged.
Fleischer J et al. The decline in hip bone density after gastric bypass surgery is associated with extent of weight loss. J Clin Endocrinol Metab 2008 Oct; 93:3735.
Comment
Although these findings should concern us, the relative effects of bariatric surgery and preexisting conditions such as vitamin D deficiency (common in obese patients) have been difficult to separate, especially because previous studies have been cross-sectional rather than longitudinal. Calcium absorption occurs mainly in the duodenum, which is bypassed in RYGB surgery; therefore, results might differ for other bariatric procedures. Nevertheless, monitoring for nutritional deficiencies and BMD is particularly important in women who undergo duodenal bypass procedures.