Table 3 Odds ratio for depression according to smoking exposure among current smokers Cumulative smoking exposure Men Unadjusted Multivariate- adjusted* Women Unadjusted Multivariate- adjusted* Light smokers [≦10.0] (n = 615) (n = 515) 1.00 (Reference) 1.00 (Reference) (n = 100) 1.00 (Reference) 1.00 (Reference) Moderate smokers [10.1 – 20.0] (n = 1,259) (n = 1,181) 0.53 (0.28-0.98) 0.71 (0.40-1.26) (n = 78) 0.58 (0.19-1.69) 0.63 (0.23-1.69) Yun et al. BMC Public Health 2012, 12:724 http://www.biomedcentral.com/1471-2458/12/724 never smoked in females (OR = 2.67, 95% CI = 1.38–5.16), but not in males (Table 2). Current smoking exposure had a significantly higher risk for depression among current-smokers in females, but not in males. Compared to light-smokers, heavy- smokers had a significantly higher risk of depression in females (OR = 3.97, 95% CI = 1.42–11.14). However, the OR of heavy-smokers for depression in males was 1.24 (95% CI = 0.73–2.09) (Table 3). Age of starting smoking did not have a significantly higher risk for depression among current-smokers. Compared to those who started smoking at ≤19 years, the ORs of those who started smoking at 20–24 years were 0.81 (95% CI = 0.52–1.27) in males and 2.18 (95% CI = 0.37–12.69) in females. ORs of those who started smoking at >20 years were 1.15 (95% CI = 0.61–2.17) in males and 0.95 (95% CI = 0.22–3.93) in females (Table 4). Duration of smoking cessation among former smo- kers did not exhibit a significantly lower risk of depression in males. We did not evaluate the relation- ships between the duration of smoking cessation and depression in females because the number of former- smokers among females was small. Compared to those who quit smoking <5 years, the OR of those who quitted smoking ≥20 years was 0.92 (95% CI = 0.39–2.14) in males (Table 5). Discussion The results of this study demonstrated a stronger associ- ation between smoking status and depression in women than in men. However, the dose–response relationship for smoking and depression among current-smokers was only significant in females. No significant associations of the age of starting smoking and duration of smoking Table 2 Odds ratio for depression according to smoking status Table 4 Odds ratio for depression according to age of starting smoking among current smokers Smoking status Smoking status Age of starting smoking Men Unadjusted Multivariate- adjusted* Women Unadjusted Multivariate- adjusted* Never smokers (n = 13,427) (n = 2,786) 1.00 (Reference) 1.00 (Reference) (n = 10,641) 1.00 (Reference) 1.00 (Reference) Former smokers (n = 2,570) Current smokers (n = 4,087) (n = 2,471) 1.66 (1.18-2.35) 1.35 (0.92-1.98) (n = 99) 4.68 (2.38-9.20) 2.67 (1.38-5.16) (n = 3,861) 1.52 (1.11-2.09) 1.77 (1.27-2.48) (n = 226) 5.30 (3.30-8.50) 3.72 (2.11-6.54) Men Unadjusted Multivariate- adjusted* Women Unadjusted Multivariate- adjusted* < 19 years (n = 1,281) (n = 1,259) 1.00 (Reference) 1.00 (Reference) (n = 22) 1.00 (Reference) 1.00 (Reference) 20 - 24 years (n = 2,014) (n = 1,980) 0.79 (0.51-1.22) 0.81 (0.52-1.27) (n = 34) 1.37 (0.24-7.82) 2.18 (0.37-12.69) ≧ 25 years (n = 789) (n = 618) 1.51 (0.84-2.71) 1.15 (0.61-2.17) (n = 171) 0.97 (0.21-4.45) 0.95 (0.22-3.93) Data are presented as mean (standard error) or odds ratio (95% confidence interval). *Adjusted for age, income status, education status, marital status, job status, drinking status, BMI, physical activity, Hypertension, Diabetes mellitus, and Cerebrovascular disease. Data are presented as mean (standard error) or odds ratio (95% confidence interval). *Adjusted for age, income status, education status, marital status, job status, amount of smoking, drinking status, BMI, physical activity, Hypertension, Diabetes mellitus, and Cerebrovascular disease. Page 4 of 7 Heavy smokers [>20.0] (n = 2,213) (n = 2,164) 0.83 (0.47-1.45) 1.24 (0.73-2.09) (n = 49) 3.65 (1.15-11.59) 3.97 (1.42-11.14) Data are presented as mean (standard error) or odds ratio (95% confidence interval). *Adjusted for age, income status, education status, marital status, job status, drinking status, BMI, physical activity, Hypertension, Diabetes mellitus, and Cerebrovascular disease. cessation with depression were observed among former- smokers. In this study, the smoking rate in women was lower than that in men. The gender difference in smoking might be due to the effects of socio-cultural factors. Sex role norms and general expectations concerning gender- appropriate behavior have had a variety of effects on gender differences in smoking [21]. Traditional sex roles lead to social pressure against women smoking [21]. Additionally, differences in the demographic and socioe- conomic characteristics of smokers and non-smokers have been reported [22-24]. The relationship between smoking and depression could be affected by these fac- tors. However, it seems unlikely that these factors affected our results, as we adjusted for them in our analysis.