PPARD and vitamin D deficiency: Firstly, activation of PPAR-δ by 1,25(OH)2D [32] will induce decreased FFAs concentrations because of increased fat oxidation and utilization of fatty acids by skeletal muscle [33]; secondly, treatment with 1,25(OH)2D could result in promotion of fatty acid synthesis and inhibition of lipolysis [34,35] in adipocytes, and hence the serum FFAs concentration was increased under vitamin D deficiency status.