The Role of Vitamin D in Weight-Related Metabolic Derangements, Inflammation and Insulin Resistance

T role of vitamin D in maintaining calcium homeostasis and bone mineralization is well-established. We investigated the effect of vitamin D on weight-related inflammation, metabolic derangements and associated histological changes of the live. Vitamin D treatment induced a significant gradual decrease in animals’ weight under high fat diet fed conditions compared to a steady increase in the weights of controls. Furthermore, vitamin D reduced the levels of inflammatory markers including TNF-α, CRP and IL-6. There were also lower concentrations of insulin and C-peptide, which indicates improvement in insulin resistance. Liver histology showed a marked accumulation of fat droplets in approximately 60-70% of hepatocytes of animals while vitamin D rendered the whole structure more normal. Transcriptional regulation of genes in tissues primarily involved in glucose homeostasis in response to vitamin D treatment revealed a general trend of up-regulation in the expression levels of insulin receptor (IR), glucose transporter-4 (Glut4), insulin receptor substrate (IRS) and vitamin D receptor (VDR) in particular under conditions resembling obesity (high fat fed animal model). These data signify an important effect of vitamin D on weightrelated insulin resistance and a protective consequence on the liver structure.