Consistent with preclinical evidence supporting its role in glucose metabolism and body composition, vitamin D supplementation was reported to improve insulin resistance and to reduce in total trunk fat mass in patients with obesity [110], to improve glycemic control in subjects with prediabetes [111], and to be inversely associated with insulin resistance [104], although not all studies point towards a beneficial effect of vitamin D on insulin sensitivity [112]. Here, INS is linked to obesity due to melanocortin 4 receptor deficiency.