Vitamin D has been suggested to favor β-cell function and to enhance insulin sensitivity by different mechanisms: the interaction with calcium flux-regulating receptors of β-cells, the reduction of the renin–angiotensin system hyperactivity, the stimulation of insulin receptor expression, the activation of the peroxisome proliferator-activated receptor delta (PPAR-δ), the deactivation of inflammatory cytokines associated with insulin resistance and the promotion of calbindin expression, which confers apoptosis protection [6]. The gene discussed is INS; the disease is Insulin resistance.