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.