Intestinal Calcium Absorption Decreases After Laparoscopic Sleeve Gastrectomy Despite Optimization of Vitamin D Status

Abstract

Context: Laparoscopic sleeve gastrectomy (LSG), now the most commonly performed bariatric operation, is a highly effective treatment for obesity. While Roux-en-Y gastric bypass is known to impair intestinal fractional calcium absorption (FCA) and negatively affect bone metabolism, LSG's effects on calcium homeostasis and bone health have not been well characterized.

Objective: We determined the effect of LSG on FCA, while maintaining robust 25-hydroxyvitamin D (25OHD) levels and recommended calcium intake.

Design, setting, participants: Prospective pre-post observational cohort study of 35 women and men with severe obesity undergoing LSG.

Main outcomes: FCA was measured preoperatively and 6 months postoperatively with a gold-standard dual stable isotope method. Other measures included calciotropic hormones, bone turnover markers, and bone mineral density (BMD) by dual-energy X-ray absorptiometry and quantitative computed tomography.

Results: Mean ± SD FCA decreased from 31.4 ± 15.4% preoperatively to 16.1 ± 12.3% postoperatively (P < 0.01), while median (interquartile range) 25OHD levels were 39 (32-46) ng/mL and 36 (30-46) ng/mL, respectively. Concurrently, median 1,25-dihydroxyvitamin D level increased from 60 (50-82) pg/mL to 86 (72-107) pg/mL (P < 0.01), without significant changes in parathyroid hormone or 24-hour urinary calcium levels. Bone turnover marker levels increased substantially, and areal BMD decreased at the proximal femur. Those with lower postoperative FCA had greater areal BMD loss at the total hip (ρ = 0.45, P < 0.01).

Conclusions: FCA decreases after LSG, with a concurrent rise in bone turnover marker levels and decline in BMD, despite robust 25OHD levels and with recommended calcium intake. Decline in FCA could contribute to negative skeletal effects following LSG.

Keywords: bariatric surgery; bone mineral density; bone turnover markers; calcium absorption; laparoscopic sleeve gastrectomy; vitamin D.

Figure 1.

Fractional calcium absorption before and 6 months after laparoscopic sleeve gastrectomy (n = 35).

Figure 2.

Scatter plot with best fit line and 95% CI (shaded) showing (A) the greater the increase in insulin-like growth factor 1 (% change), the higher the postoperative FCA, and (B) the greater the postoperative FCA, the less decrease in total hip areal bone mineral density (% change) 6 months after laparoscopic sleeve gastrectomy. Abbreviations: FCA, fractional calcium absorption.