MTHFR and major depressive disorder: After correcting for age, sex, smoking, BMI, WHR, depression, sleep, oil and salt intake, SBP, Glu, TC, TG, LDL and Hcy levels, we found that for the highest quartile of MTHFR promoter methylation level (Q4), the total OR (95% CI) of IS was 0.13 (0.07–0.24).