Bone mass decreases in morbidly obese women after long limb-biliopancreatic diversion and marked weight loss without secondary hyperparathyroidism. A physiological adaptation to weight loss?

Abstract

Objective: To investigate the effect of marked weight loss after long limb-biliopancreatic diversion (BPD-LL) on bone mass and serum calcium, 25-OH-vitamin D, and PTH levels in relation to calcium supplementation.

Background data: BPD is the most effective type of bariatric surgery, but it is followed by bone mass loss, mainly attributed to calcium and vitamin D malabsorption leading to secondary hyperparathyroidism.

Methods: Two groups, each consisting of 26 healthy, morbidly obese, premenopausal women, underwent BPD-LL. Both groups received high-calcium diets, 200 IU of vitamin D and 100 mg elemental calcium daily and group B, in addition to an extra 2 g of calcium. Bone density and biochemical markers were measured before and 12 months after BPD-LL.

Results: One year after surgery, both groups had lost an average of 55 kg of body weight; albumin-corrected calcium concentration did not change. 25-OH-vitamin D levels in group A were 17.34 +/- 8.90 pre- and 20.51 +/- 14.71 microg/L postoperatively (p = 0.058), and in group B, 15.70 +/- 9.46 and 13.52 +/- 8.16 microg/L (p = 0.489), respectively. PTH levels in group A were 38.5 +/- 12.2 before and 51.2 +/- 32.8 pg/ml after surgery (p = 0.08), and in group B, 48.1 +/- 26.3 and 52.9 +/- 29.2 pg/ml (p = 0.147), respectively. Bone formation markers (alkaline phosphatase, osteocalcin and procollagen type 1), as well as the bone resorption marker CTx, increased significantly in both groups. Bone mineral density T score was 0.862 +/- 0.988 in group A and 0.851 +/- 1.44 in group B and declined postoperatively to -0.123 +/- 1.082 and 0.181 +/- 1.285, respectively.

Conclusions: Marked weight loss after BPD-LL leads to increased bone turnover and normalization of the increased bone mass without calcium or vitamin D malabsorption and without the appearance of secondary hyperparathyroidism. We conclude that the bone mass reduction is a normal adaptation to the decreased loading of the bone following weight loss.