Background: Little is known about changes in bone mineral density (BMD) following weight loss after one-anastomosis gastric bypass (OAGB) and the role of serum vitamin D and its supplementation on bone metabolism. We evaluated BMD after OAGB as a function of vitamin D supplementation with respect to a minimum threshold of 25-hydroxy-vitamin-D [25(OH)D] concentration, which could prevent or decelerate an eventual bone loss.
Methods: Fifty bariatric patients who participated in the randomized controlled trial were included in this analysis. BMD and anthropometric measurements by DXA and laboratory parameters were assessed before (T0), at 6 (T6), and 12 months (T12) after surgery.
Results: OAGB resulted in a 36% total body weight loss with a decrease in body fat and an increase in lean body mass. A significant decrease in BMD was seen in lumbar spine by 7%, left hip 13%, and total body 1%, but not in forearm. Bone turnover markers increased significantly but with normal parathyroid hormone concentrations. Weight loss was not associated with changes in BMD. A serum 25(OH)D concentration > 50 nmol/l at T6 and T12 (adequate-vitamin-D-group; AVD) showed a significant lower bone loss, compared to the inadequate-vitamin-D-group (IVD; < 50 nmol/l). Lower bone loss in the left hip showed a strong correlation with higher 25(OH)D concentrations (r = 0.635, p = 0.003).
Conclusion: These findings support a dose effect of vitamin D supplementation on bone health and suggest that 25(OH)D concentrations need to be above 50 nmol/l at least during the first postoperative year to decelerate bone loss in patients undergoing OAGB.
Clinical trial registry number and website: Clinicaltrials.gov (NCT02092376) at https://clinicaltrials.gov /. EudraCT (2013-003546-16) at https://eudract.ema.europa.eu /.
Keywords: Bone loss; Obesity; One-anastomosis gastric bypass; Vitamin D; Weight loss.