Effects of Bariatric Surgery on Vitamin D Status and Secondary Hyperparathyroidism: A Prospective Study

Background: Morbidly obese patients have been reported to present with vitamin D insufficiency and secondary hyperparathyroidism. Scattered data are available regarding the effects of bariatric surgery on vitamin D status. We studied calcium metabolism and vitamin D status before and after bariatric surgery. Methods: In this prospective study, 64 patients (M5/F59) fulfilled the inclusion criteria (i.e. 2 calcidiol serum determinations in the winter season) among 457 morbidly obese individuals who underwent Roux-en-Y gastric bypass (RYGBP) a mean of 36 months previously. Laboratory data (serum calcium, phosphorus, creatinine, alkaline phosphatase, albumin, calcidiol, albumin and iPTH) were determined before and after RYGBP. Pre- and postoperative calcidiol levels were categorized as being normal (>50 nmol/L), insufficient (25-50 nmol/L), and deficient (<25 nmol/L). Pre- and postoperative mild secondary hyperparathyroidism was defined as iPTH >7.3 pmol/L with simultaneous normal values for creatinine, calcium and phosphorus. Results: RYGBP produced a significant weight loss coupled with a simultaneous increase in calcidiol (+28%, P<0.0005) and decrements in total alkaline phosphatase (-53%, P<0.0005) and iPTH (-74%, P=0.001). Corrected serum calcium, phosphorus, and creatinine levels were indistinguishable before and after RYGBP. Additionally, 37.5% of the patients maintained their calcidiol category, while 42.2 % improved it and 20.3% lost one category. Conclusions: RYGBP does not completely correct pre-existing vitamin D deficient states with secondary hyperparathyroidism. Low calcidiol bioavailability and or insufficient sunlight exposure do probably persist after bariatric surgery. While randomized controlled studies are warranted, it seems advisable to support vitamin D supplementation as well as increasing sunlight exposure in the morbidly obese population.