Bsm1 vitamin D receptor polymorphism and calcium homeostasis following bariatric surgery.

PURPOSE/AIM: To evaluate the association between the Bsm1 vitamin D receptor polymorphism and the calcium-vitamin D-parathormone axis following bariatric surgery.

MATERIALS AND METHODS: This cross-sectional study included 86 morbidly obese patients, who underwent either gastric bypass or sleeve gastrectomy, with a mean follow-up of four years. Calcium metabolism indices and bone turnover markers were assessed according to the presence of secondary hyperparathyroidism and the Bsm1 vitamin D receptor genotypes.

RESULTS: Secondary hyperparathyroidism (42.2% of sample) was associated with lower levels of 25hydroxyvitamin D and elevated markers of bone turnover. In subjects without secondary hyperparathyroidism, presence of the unfavorable B allele resulted in higher levels of parathormone (Bb and BB vs. bb genotype: 50.3 ± 8.2 pg/dl vs. 44.4 ± 10.7 pg/dl, p = .011, adjusted for weight loss, baseline body mass index, 25hydroxyvitamin D, surgical procedure, and duration after surgery). In the whole sample, patients bearing the unfavorable B allele exhibited lower weight loss, a parameter that was negatively associated with markers of bone resorption.

CONCLUSIONS: Secondary hyperparathyroidism is highly prevalent after bariatric surgery. Bsm1 vitamin D receptor polymorphism may have an effect in early stages of calcium metabolism imbalance, while no association is detected in patients who have already developed secondary hyperparathyroidism. Moreover, vitamin D receptor polymorphism is associated with post-surgery weight loss, a process related to bone turnover.