CRP and major depressive disorder: Among each e-cigarette use group, dual users consistently had the highest odds of depression at each CRP strata (odds were evaluated by assessing each e-cigarette category against the same non-smoking/never-vaping reference group and CRP category): CRP < 8 mg/L had an adjusted OR of 4.31 (95% CI: 2.35, 7.89), while those with CRP ≥ 8 mg/L had an adjusted OR of 7.37 (95% CI: 1.85, 29.41).