Evaluation of markers for calcium homeostasis in a population of obese adults undergoing gastric bypass operations

BACKGROUND: Gastric bypass operation has become a very common procedure for treatment of obesity. Changes in calcium absorption can result in changes in total body calcium, parathyroid hormone (PTH), and vitamin D levels. There is little known about the longterm effects of Roux-en-Y gastric bypass on calcium metabolism and bone homeostasis. STUDY DESIGN: Between January 2000 and January 2006, 535 morbidly obese patients underwent standard Roux-en-Y gastric bypass. All patients were given a standard multivitamin, vitamin D, and calcium supplement starting on day 12 after the operation. Metabolic parameters, such as serum calcium levels, vitamin D, and PTH, both pre- and postoperatively, were measured and compared at several intervals. RESULTS: Four hundred forty-four patients were followed for a minimum of 2 years. No statistical significance was found between the pre- and postoperative serum levels of calcium and vitamin D, although vitamin D levels generally increased during the first year after operation. Serum levels of PTH were substantially higher at 18 and 44 weeks after the operation. CONCLUSIONS: Hypocalcemia did not develop in any patients during the postoperative period. Increased PTH levels were observed after gastric bypass operation. This can result in mobilization of calcium from the skeleton and increased renal calcium reabsorption. Total body calcium depletion could occur from bone mobilization, if longterm calcium supplementation is not maintained. Vitamin D supplementation can assist in prevention of bone calcium depletion.