Other possible mechanisms explaining the low serum 25OHD concentrations in obesity include a reduced synthesis of vitamin D3 in the skin, a smaller skin area exposure to sunlight, a lack of outdoor activity [36, 39], and a negative feedback regulation of hepatic 25OHD synthesis exerted by elevated 1,25-dihydroxy vitamin D and parathyroid hormone concentrations [35]. This evidence concerns the gene PTH and obesity due to melanocortin 4 receptor deficiency.