Controversies in vitamin D: deficiency and supplementation after Roux-en-Y gastric bypass surgery

Changes in Bone Mineral Density Following Weight Loss Induced by One-Anastomosis Gastric Bypass in Patients with Vitamin D Supplementation

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 /.

Effect of gastric bypass on vitamin D and secondary hyperparathyroidism

Obesity as well as bariatric surgery may increase the risk for vitamin D deficiency. We retrospectively compared vitamin D levels in obese patients (n = 123) prior to bariatric surgery and 1 year postoperatively. We also evaluated parathyroid hormone levels (PTH) 1 year after surgery. A higher percentage of patients had baseline vitamin D deficiency (86%), defined as 25-hydroxy vitamin D <32 ng/mL, compared with the 1-year (post-surgical) levels, (70%; p < 0.001). Body mass index (BMI) inversely correlated with vitamin D deficiency at baseline (r = -0.3, p = 0.06) and at the postoperative follow-up (r = -0.2, p = 0.013). One third of the postoperative population had secondary hyperparathyroidism, defined by a serum PTH level >62 pg/mL; however, postoperative PTH and vitamin D levels were unrelated (r = -0.001, p = 0.994). Pre- and postoperative vitamin D levels were inversely correlated with BMI. Secondary hyperparathyroidism was observed in 33% of patients postoperatively; however, this did not correlate with vitamin D.

Obesity is associated with increased parathyroid hormone levels independent of glomerular filtration rate in chronic kidney disease

The objective of the study was to examine the relationship of obesity and parathyroid hormone (PTH) levels among persons with chronic kidney disease (CKD). This was a cross-sectional analysis of 4551 participants in the National Kidney Foundation-Kidney Early Evaluation Program found to have CKD (estimated glomerular filtration rate <60 mL/[min 1.73 m(2)]) examining the relationship of body mass index (BMI) and PTH levels. In unadjusted analysis, PTH levels increased with increasing BMI quartiles. After adjustment for age, race, sex, diabetes, calcium, phosphorus, estimated glomerular filtration rate, and presence of microalbuminuria, PTH levels were 7.3% (P = .008), 11.9% (P < .0001), and 18.1% (P < .0001) higher in the second, third, and fourth BMI quartiles, respectively, as compared with the first quartile. In a companion analysis, higher BMI was associated with increased odds of having an elevated PTH measurement (>70 pg/mL). Compared with the first quartile, odds ratios for elevated PTH were 1.26 (95% confidence interval, 1.06-1.50; P = .01), 1.38 (1.15-1.65, P = .0005), and 1.66 (1.37-2.00, P < .0001) for the second, third, and fourth quartiles, respectively. We found no effect modification by race, diabetes, or presence of microalbuminuria. Therefore, in a large community-dwelling population with CKD, the presence of obesity and of increasing BMI is associated with higher PTH levels independent of measured confounders and may be an additional target in the management of secondary hyperparathyroidism in CKD.