Table 2. Risk of developing lung cancer in relationship to baseline menstrual and reproductive factors.
| Factors | Lung cancer | Adenocarcinoma | |||
|---|---|---|---|---|---|
| Cases (N=1,529) | HR† (95% CI) | Cases (N=1,202) | HR† (95% CI) | ||
| Age at menarche, year | |||||
| <13 | 137 | Ref | 107 | Ref | |
| 13 | 269 | 1.12 (0.91–1.37) | 207 | 1.11 (0.88–1.40) | |
| 14 | 363 | 1.13 (0.92–1.37) | 275 | 1.11 (0.88–1.39) | |
| 15 | 311 | 1.26 (1.03–1.54) | 254 | 1.33 (1.06–1.68) | |
| ≥16 | 449 | 1.43 (1.17–1.73) | 359 | 1.49 (1.20–1.86) | |
| Menopause status‡ | |||||
| Natural menopause | 1,200 | Ref | 921 | Ref | |
| Surgical menopause | 81 | 1.64 (1.31–2.06) | 72 | 1.85 (1.45–2.35) | |
| Age at menopause‡, year | |||||
| <45 | 78 | Ref | 68 | Ref | |
| 45–49 | 385 | 0.78 (0.61–1.00) | 301 | 0.71 (0.55–0.93) | |
| 50–54 | 737 | 0.86 (0.68–1.08) | 561 | 0.76 (0.59–0.98) | |
| ≥55 | 81 | 0.95 (0.69–1.29) | 63 | 0.86 (0.61–1.22) | |
| Reproductive period‡, year | |||||
| <30 | 92 | Ref | 79 | Ref | |
| 30–34 | 402 | 0.83 (0.67–1.05) | 308 | 0.85 (0.67–1.06) | |
| 35–39 | 690 | 0.80 (0.65–1.00) | 536 | 0.83 (0.67–1.03) | |
| ≥40 | 97 | 0.80 (0.60–1.16) | 70 | 0.84 (0.63–1.12) | |
| Age at first live birth, year | |||||
| Nulliparous | 31 | 1.23 (0.85–1.77) | 23 | 1.20 (0.78–1.83) | |
| <25 | 469 | Ref | 345 | Ref | |
| 25–29 | 901 | 1.31 (1.17–1.47) | 728 | 1.43 (1.25–1.63) | |
| ≥30 | 128 | 1.31 (1.07–1.60) | 106 | 1.44 (1.15–1.80) | |
| Duration of breastfeeding, month | |||||
| 0 | 191 | Ref | 154 | Ref | |
| 1–12 | 963 | 0.99 (0.84–1.15) | 765 | 0.99 (0.83–1.18) | |
| ≥13 | 375 | 0.82 (0.69–0.98) | 283 | 0.81 (0.66–0.99) | |
| Benign breast disease | |||||
| No | 989 | Ref | 759 | Ref | |
| Yes | 540 | 1.27 (1.13–1.44) | 443 | 1.33 (1.16–1.52) | |
| Surgery on the reproductive system | |||||
| No | 1,293 | Ref | 1,012 | Ref | |
| Yes | 236 | 1.15 (1.00–1.33) | 190 | 1.15 (0.98–1.35) | |
†, adjusted for age at enrollment (continuous), education (low, medium, or high), BMI (underweight, normal, overweight or obese), smoking status (current, former or never-smoker), exposures to environmental tobacco smoke (yes or no), exposure to cooking smoke (none, little, some, or much), occupational exposures (yes or no), history of chronic respiratory disease (yes or no) and family history of lung cancer (yes or no). Province of different economic region was treated as a random variable considering within-cluster correlation. ‡, among postmenopausal women only. HR, hazard ratio; CI, confidence interval.