Adequate vitamin D supplementation does not ameliorate bone loss following long limb-biliopancreatic diversion in morbidly obese women

Abstract

Objectives: The objective of this study is to investigate the effect of adequate vitamin D supplementation on bone mineral density (BMD) following long limb-biliopancreatic diversion (LL-BPD), a malabsorptive bariatric operation.

Background: Marked weight loss following bariatric surgery is associated with significant decrease in BMD, attributed to the weight loss and to nutritional, mineral, and vitamin D deficiencies resulting in secondary hyperparathyroidism.

Methods: Two groups, of 35 and 37 healthy, obese (BMI, 50.4 + 6.6 and 46.5 + 4.8 g/cm²), premenopausal, normally menstruating women underwent LL-BPD. Both groups received high-calcium diets, 600 IU of vitamin D, and 1000 mg elemental calcium daily, while group B received an extra dose of vitamin D (10,000 IU/day) during the first postoperative month, followed by dose adjustment in order to maintain 25OHD concentration higher than 30 μg/L. Areal BMD (aBMD) was measured at the lumbar spine preoperatively and 1 year postoperatively.

Results: One year postoperatively, BMI decreased by approximately 19 kg/m² in both groups, while 25-OH-vitamin D levels did not change in group A (18.7 + 9.1 to 20.2 + 13.0 μg/L, (p = 0.57)) and increased in group B (15.58 ± 5.73 to 52.97 ± 15.46 μg/L, (p = < 0.001). PTH levels increased in group A (from 38.5 ± 12.2 to 51.2 ± 32.8 pg/ml) (p = 0.047) and decreased in group B (from 51.61 ± 18.7 to 45.1 ± 17.8 pg/ml) (p = 0.042). Lumbar spine aBMD decreased similarly in both groups (p = 0.311, for the comparison between groups) from 1.198 + 0.14 to 1.103 + 0.15 g/cm² in group A (p < 0.001) and from 1.157 + 0.14 to 1.076 + 0.14 g/cm² in group B (p < 0.001) and Z-score from 0.93 + 0.97 to 0.19 + 1.02, (p < 0.001) and from 1.15 + 1.29 to 0.419 + 1.28, (p < 0.001), respectively.

Conclusions: LL-BPD leads to similar and significant bone mass reduction 1 year postoperatively, irrespective of adequate vitamin D replacement and in the absence of secondary hyperparathyroidism.

Keywords: Bariatric surgery; Bone mass; Obesity; Secondary hyperparathyroidism; Vitamin D.