At the baseline, patients with morbid obesity were characterized by significantly lower levels of active vitamin D metabolite 1,25(OH)2D3 (20 (10; 37) vs. 39 (33; 50) pg/mL, p < 0.001), lower serum calcium levels (2.24 (2.20; 2.32) vs. 2.31 (2.25; 2.35) mmol/L, p = 0.009) and magnesium levels (0.79 (0.72; 0.82) vs. 0.82 (0.78; 0.85) mmol/L, p = 0.043) with simultaneous similar 25(OH)D3 and PTH levels (p > 0.05) (Table 4). This evidence concerns the gene PTH and morbid obesity.