Yun et al. BMC Public Health 2012, 12:724 http://www.biomedcentral.com/1471-2458/12/724 Page 3 of 7 with depression were significantly older than those with- out depression in both sexes (males: 46.5 ± 0.4 vs. 56.4 ± 2; females: 50.1 ± 0.5 vs. 58.6 ± 1.8). Subjects with depression had a significantly higher percentage of current/former smokers than subjects without depres- sion in both sexes (males: 45.0% vs. 49.1%; females: 1.6% vs. 7.8%). Subjects with depression had significantly higher mean pack-years of smoking than those without depression in both sexes (males: 13.8 ± 0.4 vs. 20.3 ± 2.4; females: 0.2 ± 0.2 vs. 1.3 ± 0.5). Subjects with depression did not ex- hibit a significantly lower mean age of starting smoking than those without depression in both sexes (males: 20.7 ± 0.1 vs. 20.8 ± 0.6; females: 31.0 ± 2.0 vs. 35.6 ± 5.3). Subjects with depression had a significantly longer dur- ation of quitting smoking than those without depression in males, but not in females (males: 13.0 ± 0.6 vs. 17.9 ± 3.9; females: 16.3 ± 4.0 vs. 15.5 ± 6.5) (Table 1). Smoking status and depression We found interaction effects between sex and current smoking on depression in the survey logistic regression analyses (p = 0.009 for interaction). Currents smokers had a significantly higher risk of de- pression than those who had never smoked in both males (OR = 1.77, 95% CI = 1.27–2.48) and females (OR = 3.72, 95% CI = 2.11–6.54). However, former smokers had a sig- nificantly higher risk of depression than those who had Table 1 General characteristics of the study population with and without depression (n = 20,084) Men (n = 9,118) Non-depression (n = 8,702) 46.5 ± 0.4 Depression (n = 416) 56.4 ± 2.1* Women (n = 10,966) Non-depression Depression (n = 10,094) (n = 872) 50.1 ± 0.5 58.6 ± 1.8* 2,687 (30.9) 2,333 (24.0) 3,682 (45.0) 13.8 ± 0.4 20.7 ± 0.1 13.0 ± 0.6 2,494 (20.1) 2,127 (21.1) 1,655 (21.8) 2,421 (36.8) 805 (5.8) 3,360 (28.3) 4,537 (65.8) 6,573 (68.5) 2,129 (31.4) 1,332 (19.5) 5,814 (61.2) 1,558 (19.2) 1,607 (13.7) 715 (6.5) 363 (3.0) 24.0 ± 0.2 2,971 (33.2) 99 (22.1)* 138 (28.7) 179 (49.1) 20.3 ± 2.4* 20.8 ± 0.6 17.9 ± 3.9* 260 (53.6)* 75 (18.3) 27 (9.7) 53 (18.2) 116 (22.2)* 176 (38.0) 123 (39.7) 255 (54.2)* 160 (45.7) 20 (6.8)* 155 (37.1) 241 (56.0) 118 (24.6)* 63 (14.5)† 65 (8.9)* 24.2 ± 1.8 82 (19.4)* 9,843 (97.7) 76 (0.3) 175 (1.6) 0.2 ± 0.2 31.0 ± 2.0 16.3 ± 4.0 3,735 (26.7) 2,256 (20.6) 1,647 (19.2) 2,450 (33.3) 3,153 (22.1) 3,497 (29.4) 3,441 (48.4) 6,482 (64.4) 3,611 (35.5) 982 (13.9) 4,518 (36.9) 4,594 (49.0) 2,475 (18.3) 766 (5.9) 413 (3.2) 24.6 ± 0.4 2,608 (23.8) 798 (89.3)† 23 (2.8) 51 (7.8) 1.3 ± 0.5 35.6 ± 5.3 15.5 ± 6.5* 538 (53.2)* 129 (15.9) 94 (15.0) 110 (15.7) 489 (48.3)* 209 (22.5) 174 (29.0) 363 (40.2)* 509 (59.7) 43 (6.8)* 237 (25.1) 592 (68.0) 319 (33.8)* 119 (12.6)† 100 (9.8)* 28.1 ± 2.1* 164 (16.8)* Characteristics Age (years) Smoking status Never smokers Former smokers Current smokers Pack-years of smoking Age of starting smoking Duration of smoking cessation Household Income < one million won < two million won < three million won ≧ three million won Education level Uneducated Elementary and Middle school High school and College Marital status Married/partnered Never married/non-partnered Job status Non-manual Manual Others Hypertension Diabetes Mellitus Cerebrovascular disease Body Mass Index (BMI) Physical activity Data are presented as mean (standard error) or unweighted number (weighted percent). * p <0.001. † p <0.05.