Although the mechanisms explaining the link between CVD and depression are complex and remain unclear, obesity, MetS, reduced insulin sensitivity, elevations in plasma homocysteine levels, endothelial dysfunction, increased production of pro-inflammatory cytokines or a single-nucleotide polymorphism in the BDNF gene (BDNFVal66Met) are plausible candidates [11,26]. Here, INS is linked to major depressive disorder.