Table 2.
Adjusted Hazard Ratios for Lung Cancer Deaths among Never-Smokers in Relation to Exposure to Household Air Pollution and Secondhand Tobacco Smoke in China Kadoorie Biobank (2004–2008)
| Lung Cancer Deaths |
Multivariable Model* |
|||
|---|---|---|---|---|
| Exposures | Yes (%) n = 979 | No (%) n = 322,815 | HR (95% CI) | P Value† |
| Sex, n (%) | ||||
| Men | 161 (16.5) | 36,322 (11.3) | — | — |
| Women | 818 (83.5) | 286,493 (88.7) | — | — |
| Exposure to household air pollution | ||||
| Status of ever exposure, n (%) | ||||
| Never | 96 (9.8) | 49,140 (15.2) | 1.00 (Reference) | 0.250 |
| Ever | 883 (90.2) | 273,675 (84.8) | 1.15 (0.91–1.45) | — |
| Duration exposed, mean (SD), yr | 31.2 (21.3) | 24.4 (19.2) | — | — |
| Duration exposed, per unit change of 5 yr | — | — | 1.04 (1.01–1.06) | 0.009 |
| Duration exposed, n (%), yr | ||||
| 0 | 96 (9.8) | 49,140 (15.2) | 1.00 (Reference) | 0.018 (trend) |
| 0–10 | 105 (10.7) | 39,652 (12.3) | 1.14 (0.86–1.51) | — |
| 10–20 | 118 (12.1) | 59,276 (18.4) | 0.95 (0.72–1.25) | — |
| 20–30 | 168 (17.2) | 58,965 (18.3) | 1.26 (0.96–1.65) | — |
| 30–40 | 155 (15.8) | 49,135 (15.2) | 1.34 (1.01–1.79) | — |
| 40–50 | 161 (16.5) | 34,515 (10.7) | 1.53 (1.14–2.07) | — |
| >50 | 176 (18.0) | 32,132 (10.0) | 1.27 (0.93–1.74) | — |
| Exposure to secondhand smoke | ||||
| Lived with a person who smoked for >6 mo | ||||
| Never | 230 (23.5) | 65,726 (20.4) | 1.00 (Reference) | 0.710 |
| Past | 284 (29.0) | 79,971 (24.8) | 0.93 (0.77–1.11) | — |
| Current | 465 (47.5) | 177,118 (54.9) | 0.96 (0.81–1.14) | — |
| Duration of living with a person who smoked among those who reported current exposure at baseline‡, mean (SD), yr | 38.7 (17.7) | 34.3 (15.2) | 1.00 (1.00–1.01) | 0.580 |
| Status of ever exposure, n (%) | ||||
| Never | 124 (12.7) | 29,121 (9.0) | 1.00 (Reference) | 0.460 |
| Ever | 855 (87.3) | 293,694 (91.0) | 0.93 (0.76–1.13) | — |
| Duration of living with a person who smoked for >6 mo and frequency/duration of exposure at baseline | ||||
| Never lived with a person who smoked and never or occasionally exposed at baseline | 190 (19.4) | 52,243 (16.2) | 1.00 (Reference) | 0.520 |
| Either never lived with a person who smoked or never or occasionally exposed at baseline | 229 (23.4) | 67,030 (20.8) | 1.07 (0.88–1.30) | — |
| Ever lived with a person who smoked for ⩽30 yr and exposed at least 1 d/wk at baseline | 160 (16.3) | 80,621 (25.0) | 0.93 (0.75–1.16) | — |
| Ever lived with a person who smoked for >30 yr and exposed <7 h/wk at baseline | 261 (26.7) | 68,809 (21.3) | 0.98 (0.80–1.19) | — |
| Ever lived with a person who smoked for >30 yr and exposed ⩾7 h/wk at baseline | 139 (14.2) | 54,112 (16.8) | 0.89 (0.71–1.12) | — |
Definition of abbreviations: CI = confidence interval; HR = hazard ratio.
*
Multivariable model with age as the underlying time variable and adjusted for sex, height, region of residence, highest education, occupation, stove ventilation, solid fuel use for heating, use of cooking oil, physical activity, body mass index, diabetes, and intake of dairy products.
†
Type 3 test for Cox regression.
‡
Confined to the participants who reported currently living with a person who smoked at baseline (177,583); among them, 465 had the outcome of lung cancer death.