In particular, a negative correlation was observed in obese subjects between vitamin D concentrations and obesity-related parameters (weight, BMI, waist circumference, fat mass; visceral fat; total cholesterol, LDL cholesterol) and glucose metabolism-related parameters (fasting blood glucose, blood glucose at 120 min, insulin, HOMA index). The gene discussed is INS; the disease is obesity due to melanocortin 4 receptor deficiency.