INS and major depressive disorder: It is known that CRP, insulin and leptin interact in metabolism pathways and it was proposed that their joint measurement may be an improved marker for cardiovascular disease, obesity and depression (Hribal, Fiorentino, & Sesti, 2014; Milaneschi, Simmons, van Rossum, & Penninx, 2019; Sudhakar, Silambanan, Chandran, Prabhakaran, & Ramakrishnan, 2018).