SIRT1 and obesity due to melanocortin 4 receptor deficiency: In the same sense, a clinical trial with 90 men and women with type 2 diabetes and overweight/obesity who were supplemented with vitamin D showed that there was a parallel significant increase in the plasma levels of irisin and SIRT1 supporting the link between these two molecules, considering that SIRT1 stimulates PGC-α which in turn enhances irisin production (Table 2).