Table 1. Baseline characteristics of current and former smokers, by age at onset of smoking.
| Variable | Age at onset of smoking (36 673 men) | Age at onset of smoking (4224 women) | |||||||
| ≥20 years (n = 26 387) |
18–19 years (n = 7920) |
≤17 years (n = 2366) |
P valuea | ≥20 years (n = 3878) |
18–19 years (n = 270) |
≤17 years (n = 76) |
P valuea | ||
| No. of current smokers (%) | 18 496 (70.1) | 5317 (67.1) | 1577 (66.7) | <0.0001 | 3172 (81.8) | 196 (72.6) | 58 (76.3) | <0.0005 | |
| No. of former smokers (%) | 7891 (29.9) | 2603 (32.9) | 789 (33.3) | 706 (18.2) | 74 (27.4) | 18 (23.7) | |||
| Age, years (SD) | 52.1 (8.1) | 49.8 (7.8)b | 50.8 (7.9)b | <0.0001 | 50.2 (7.9) | 45.7 (6.1)b | 47.9 (76)b | <0.0001 | |
| Follow-up, years (SD) | 11.2 (3.8) | 11.0 (3.7)b | 11.1 (3.7) | <0.0001 | 11.0 (3.8) | 10.9 (3.7) | 10.1 (3.7) | <0.0001 | |
| No. of cigarettes per day (SD) | 22.4 (11.6) | 25.0 (12.2)b | 26.3 (12.8)b | <0.0001 | 13.8 (8.5) | 18.6 (10.6)b | 20.9 (10.3)b | <0.0001 | |
| Duration of smoking, years (SD) | 27.0 (9.8) | 27.8 (9.7)b | 30.8 (10.5)b | <0.0001 | 19.2 (9.7) | 23.7 (9.5)b | 28.4 (13.0)b | <0.0001 | |
| Pack-years of smoking (SD) | 612.9 | 707.4b | 829.4b | <0.0001 | 283.6 | 447.2b | 555.5b | <0.0001 | |
| (387.0) | (421.0) | (486.2) | (245.0) | (339.9) | (342.4) | ||||
| Alcohol consumption (%) | |||||||||
| Men | Women | ||||||||
| None | None | 21.8 | 20.5 | 23.9 | <0.0001 | 53.4 | 36.2 | 43.1 | <0.0001 |
| monthly | monthly | 8.4 | 7.3 | 6.7 | 13.3 | 17.7 | 8.3 | ||
| <150 g/week | <100 g/week | 21.6 | 19.1 | 17.0 | 15.0 | 14.6 | 5.6 | ||
| 150–299 g/week | ≥100 g/week | 22.1 | 21.6 | 17.4 | 18.2 | 31.5 | 43.1 | ||
| 300–449 g/week | 14.0 | 16.6 | 15.2 | ||||||
| ≥450 g/week | 12.0 | 14.9 | 19.8 | ||||||
| Body mass | ≤18.9 | 5.4 | 5.0 | 5.9 | 0.1075 | 10.5 | 14.4 | 9.2 | 0.6456 |
| index (%) | 19.0–20.9 | 15.7 | 15.7 | 15.3 | 19.4 | 22.2 | 22.4 | ||
| 21.0–22.9 | 26.8 | 25.8 | 26.1 | 25.1 | 24.4 | 30.3 | |||
| 23.0–24.9 | 26.8 | 27.3 | 26.0 | 18.6 | 16.7 | 14.5 | |||
| 25.0–26.9 | 15.8 | 16.0 | 15.1 | 13.1 | 11.1 | 11.8 | |||
| 27.0–29.9 | 7.7 | 8.3 | 9.2 | 9.1 | 7.8 | 6.6 | |||
| ≥30.0 | 1.9 | 1.9 | 2.4 | 4.2 | 3.3 | 5.3 | |||
| Green vegetable | Not every day | 76.8 | 81.7 | 80.3 | <0.0001 | 75.9 | 83.3 | 88.2 | 0.0012 |
| intake (%) | every day | 23.2 | 18.3 | 19.7 | 24.1 | 16.7 | 11.8 | ||
SD: standard deviation.
aPearson’s chi-square test and analysis of variances were used to evaluate differences between groups.
bSignificant difference from subjects who started smoking after the age of 20 years (P < 0.05 on Dunnett’s t-test).