Table 5.
Passive smoking in relation to the incidence of breast cancer among nonsmokers
| Passive smoking status | Person-years | Cases | Age-adjusted HR(95% CI) | Covariate-adjusted HR(95% CI)* |
|---|---|---|---|---|
| Exposure to parental smoking when living with them | ||||
| Neither smoked | 342457 | 1156 | 1.0 | 1.0 |
| Mother only | 33107 | 81 | 0.80 (0.63, 1.00) | 0.83 (0.66, 1.05) |
| Father only | 378859 | 1313 | 1.02 (0.95, 1.11) | 1.01 (0.93, 1.10) |
| Both parents | 120522 | 333 | 0.91 (0.81, 1.03) | 0.90 (0.79, 1.03) |
| Exposure at work: | ||||
| Never at work | 186896 | 637 | 1.0 | 1.0 |
| Occasional | 362062 | 1210 | 1.00 (0.90, 1.10) | 0.99 (0.89, 1.09) |
| Regular | 210505 | 621 | 0.89 (0.79, 0.99) | 0.87 (0.78, 0.98) |
| Exposure at home: | ||||
| Never at home | 424368 | 1374 | 1.0 | 1.0 |
| Occasional | 207918 | 721 | 1.05 (0.95, 1.15) | 1.06 (0.97, 1.17) |
| Regular | 126169 | 402 | 0.98 (0.88, 1.10) | 1.02 (0.90, 1.14) |
| Years with someone who smokes: | ||||
| Never or less than 1 year | 384292 | 1243 | 1.0 | 1.0 |
| 1–4 years | 83662 | 290 | 1.09 (0.96, 1.24) | 1.09 (0.96, 1.24) |
| 5–9 years | 65670 | 215 | 0.96 (0.83, 1.11) | 0.98 (0.84, 1.13) |
| 10–19 years | 135986 | 423 | 0.96 (0.86, 1.07) | 0.96 (0.86, 1.08) |
| 20 – 29 years | 121069 | 404 | 0.95 (0.85, 1.07) | 0.96 (0.85, 1.08) |
| 30 – 39 years | 66210 | 249 | 0.93 (0.80, 1.07) | 0.97 (0.84, 1.13) |
| 40+ years | 13605 | 50 | 0.96 (0.72, 1.28) | 0.99 (0.74, 1.32) |
| P for trend: | 0.17 | 0.24 | ||
| Index of passive smoking: | ||||
| Neither at work nor at home | 139088 | 449 | 1.0 | 1.0 |
| Occasional exposure at home or work of <20 years | 279151 | 921 | 1.09 (0.97, 1.22) | 1.09 (0.97, 1.22) |
| Occasional exposure at home or work of ≥20 years | 87259 | 296 | 0.97 (0.83, 1.12) | 1.00 (0.86, 1.16) |
| Regular exposure at home or work of <20 years | 89980 | 263 | 0.99 (0.85, 1.16) | 0.99 (0.85, 1.16) |
| Regular exposure at home or work of ≥20 years | 54846 | 180 | 0.96 (0.81, 1.14) | 0.97 (0.81, 1.16) |
Adjusted for age (continuous), family history of breast cancer (yes, no), history of benign breast disease (yes, no), BMI (continuous), BMI at age 18 (continuous), height (continuous), alcohol consumption (0, 0.1–4.9, 5–14.9, ≥15 grams/day), age at menarche (≤11, 12, 13, 14, ≥15 years), parity (0, 1, 2, 3, ≥4), age at first birth (nulliparous, ≤24 years, 25–29 years, 30–34 years, ≥35 years), physical activity (<1, 1–<2, 2–<4, 4–<7, ≥7 hours/week), OC use (never, ever for <1 year, ever for 1–4 years, ever for 5–10 years, ever for >10 years), menopausal status (premenopause, postmenopause, dubious), postmenopausal hormone use (never, past for <5 years, past for ≥5 years, current for <5 years, current for ≥5 years), and age at menopause (continuous). Passive smoking at home and passive smoking at work were adjusted for each other. Exposure to parental smoking in childhood was adjusted for in analysis on passive smoking in adulthood.