Schafer Anne L, Weaver Connie M, Black Dennis M, Wheeler Amber L, Chang Hanling, Szefc Gina V, Stewart Lygia, Rogers Stanley J, Carter Jonathan T, Posselt Andrew M, Shoback Dolores M, Sellmeyer Deborah E
Medical Service, San Francisco Veterans Affairs Medical Center, San Francisco, CA, USA.
Department of Medicine, University of California, San Francisco, CA, USA.
J Bone Miner Res. 2015 Aug;30(8):1377-85. doi: 10.1002/jbmr.2467. Epub 2015 May 21.
Roux-en-Y gastric bypass (RYGB) surgery has negative effects on bone, mediated in part by effects on nutrient absorption. Not only can RYGB result in vitamin D malabsorption, but the bypassed duodenum and proximal jejunum are also the predominant sites of active, transcellular, 1,25(OH)2 D-mediated calcium (Ca) uptake. However, Ca absorption occurs throughout the intestine, and those who undergo RYGB might maintain sufficient Ca absorption, particularly if vitamin D status and Ca intake are robust. We determined the effects of RYGB on intestinal fractional Ca absorption (FCA) while maintaining ample 25OHD levels (goal ≥30 ng/mL) and Ca intake (1200 mg daily) in a prospective cohort of 33 obese adults (BMI 44.7 ± 7.4 kg/m(2)). FCA was measured preoperatively and 6 months postoperatively with a dual stable isotope method. Other measures included calciotropic hormones, bone turnover markers, and BMD by DXA and QCT. Mean 6-month weight loss was 32.5 ± 8.4 kg (25.8% ± 5.2% of preoperative weight). FCA decreased from 32.7% ± 14.0% preoperatively to 6.9% ± 3.8% postoperatively (p < 0.0001), despite median (interquartile range) 25OHD levels of 41.0 (33.1 to 48.5) and 36.5 (28.8 to 40.4) ng/mL, respectively. Consistent with the FCA decline, 24-hour urinary Ca decreased, PTH increased, and 1,25(OH)2 D increased (p ≤ 0.02). Bone turnover markers increased markedly, areal BMD decreased at the proximal femur, and volumetric BMD decreased at the spine (p < 0.001). Those with lower postoperative FCA had greater increases in serum CTx (ρ = -0.43, p = 0.01). Declines in FCA and BMD were not correlated over the 6 months. In conclusion, FCA decreased dramatically after RYGB, even with most 25OHD levels ≥30 ng/mL and with recommended Ca intake. RYGB patients may need high Ca intake to prevent perturbations in Ca homeostasis, although the approach to Ca supplementation needs further study. Decline in FCA could contribute to the decline in BMD after RYGB, and strategies to avoid long-term skeletal consequences should be investigated.
Roux-en-Y胃旁路术（RYGB）对骨骼有负面影响，部分是通过对营养物质吸收的影响介导的。RYGB不仅会导致维生素D吸收不良，而且被绕过的十二指肠和空肠近端也是活跃的、经细胞的、1,25(OH)₂D介导的钙（Ca）吸收的主要部位。然而，钙的吸收发生在整个肠道，接受RYGB手术的人可能维持足够的钙吸收，特别是如果维生素D状态和钙摄入量充足的话。我们在33名肥胖成年人（BMI 44.7±7.4kg/m²）的前瞻性队列中，在维持充足的25OHD水平（目标≥30ng/mL）和钙摄入量（每日1200mg）的情况下，确定了RYGB对肠道钙分数吸收（FCA）的影响。术前和术后6个月用双稳定同位素法测量FCA。其他测量指标包括钙调节激素、骨转换标志物以及通过双能X线吸收法（DXA）和定量CT（QCT）测量的骨密度。平均6个月体重减轻32.5±8.4kg（占术前体重的25.8%±5.2%）。尽管术前和术后25OHD水平的中位数（四分位间距）分别为41.0（33.1至48.5）和36.5（28.8至40.4）ng/mL，但FCA从术前的32.7%±14.0%降至术后的6.9%±3.8%（p<0.0001）。与FCA下降一致，24小时尿钙减少，甲状旁腺激素（PTH）升高，1,25(OH)₂D升高（p≤0.02）。骨转换标志物显著增加，股骨近端的面积骨密度降低，脊柱的体积骨密度降低（p<0.001）。术后FCA较低的患者血清I型胶原交联C末端肽（CTx）升高幅度更大（ρ=-0.43，p=0.01）。在6个月内，FCA和骨密度的下降没有相关性。总之，即使大多数25OHD水平≥30ng/mL且钙摄入量推荐，RYGB术后FCA仍显著下降。RYGB患者可能需要高钙摄入量以防止钙稳态紊乱，尽管补钙方法需要进一步研究。FCA下降可能导致RYGB术后骨密度下降，应研究避免长期骨骼后果的策略。
