CRP and major depressive disorder: The IVW method supported evidence for associations of genetically-predicted lifetime smoking index with risk of depression (ORSmk–Dep = 2.01, 95% CI : 1.71–2.37, p < 0.001), and CRP levels (ORSmk–CRP = 1.40, 95% CI: 1.27 − 1.55, p < 0.001).