Table 2. Hazard ratios (HR) of total cancer incidence and lung cancer incidence in men and women, by age at onset of smoking.

Age at onset of smoking (years)	Person-years of follow-up	Total cancer incidence			Lung cancer incidence
		No. of cases	HR1a 95% CI	HR2b 95% CI	No. of cases	HR1a 95% CI	HR2b 95% CI
Men
Current and former smokers
≥20	296 025.08	3049	1.00	1.00	474	1.00	1.00
18–19	87 505.42	802	1.07 (0.99–1.16)	1.06 (0.97–1.16)	114	1.02 (0.83–1.26)	1.03 (0.82–1.29)
≤17	26 189.10	271	1.08 (0.95–1.27)	1.06 (0.92–1.22)	56	1.48 (1.11–1.96)	1.40 (1.03–1.89)
		trend	P = 0.07	P = 0.18		P = 0.03	P = 0.08
Current smokers
≥20	207 736.13	2135	1.00	1.00	389	1.00	1.00
18–19	58 719.42	542	1.12 (1.02–1.23)	1.10 (1.00–1.21)	92	1.12 (0.89–1.41)	1.06 (0.84–1.34)
≤17	17 260.66	192	1.17 (1.01–1.36)	1.14 (0.98–1.33)	41	1.40 (1.01–1.94)	1.34 (0.96–1.86)
		trend	P = 0.005	P = 0.02		P = 0.04	P = 0.11
Former smokers
≥20	88 288.95	914	1.00	1.00	85	1.00	1.00
18–19	28 792.00	260	1.02 (0.89–1.18)	0.92 (0.74–1.16)	22	0.93 (0.57–1.53)	1.04 (0.45–2.40)
≤17	8928.44	79	0.95 (0.75–1.20)	0.76 (0.52–1.10)	15	2.05 (1.16–3.65)	2.42 (1.04–5.64)
		trend	P = 0.89	P = 0.13		P = 0.08	P = 0.09
Women
Current and former smokers
≥20	42 595.44	249	1.00	1.00	33	1.00	1.00
18–19	2885.40	10	0.76 (0.40–1.45)	0.61 (0.28–1.30)	1	0.75 (0.10–5.54)	0.69 (0.09–5.19)
≤17	769.31	5	1.29 (0.52–3.17)	1.44 (0.59–3.55)	3	8.07 (2.34–27.85)	8.04 (2.29–28.30)
		trend	P = 0.90	P = 0.81		P = 0.01	P = 0.01

^aHR1 was adjusted for geographical area (categorical), weekly ethanol intake (none, monthly, <150 g, 150–299 g, 300–449 g, ≥450 g for men, and none, monthly, <100 g, ≥100 g for women), body mass index (≤18.9, 19–20.9, 21.0–22.9, 23.0–24.9, 25.0–26.9, 27.0–29.9, ≥30.0) green vegetable intake (every day, not every day), and age in years at baseline (continuous).

^bHR2 was adjusted for all variables in HR1, plus number of cigarettes per day (continuous).