Environmental factors that influence levels of circulating vitamin D such as dietary selection (oily fish, egg yolks, mushrooms and fortified milk) [52], skin exposure to UVB irradiation [53] and the use of sunscreens that absorb UVB radiation [54], obesity [55], air pollution, aging, and so on [56] also regulate VDR gene expression. Here, VDR is linked to obesity due to melanocortin 4 receptor deficiency.