PTH and secondary hyperparathyroidism: Our results are generally consistent with the previous studies regarding the correlation of PTH and BMI [13,14], the prevalence of secondary hyperparathyroidism and low vitamin D levels [10,11,12], low baseline 1,25(OH)2D3 levels [19,20] and their increase during the follow-up [26,27,28,29], and stable levels of 24,25(OH)2D3 after the surgery [31].