Table 2.
Cumulative coal use during follow-up and risk of ischemic heart disease and stroke mortality among non-smoking women in the Xuanwei cohort, 1976–2011
| Ischaemic heart disease cases | HR (95% CI)a | P-value | Stroke cases | HR (95% CI)a | P-value | |
|---|---|---|---|---|---|---|
| Lifetime smoky or smokeless coal users | ||||||
| Tertile 1 (≤28 ton-years) | 10 | 1.0 (ref) | 76 | 1.0 (ref) | ||
| Tertile 2 (29–64 ton-years) | 30 | 2.6 (1.1–6.4) | 0.04 | 144 | 1.2 (0.9–1.7) | 0.30 |
| Tertile 3 (>64 ton-years) | 65 | 5.3 (1.9–15.1) | 0.002 | 143 | 1.2 (0.8–1.9) | 0.34 |
| >64–85 ton-years | 28 | 4.9 (1.7–14.2) | 0.004 | 77 | 1.2 (0.8–1.7) | 0.34 |
| >85 ton-years | 37 | 6.8 (2.2–21.3) | 0.001 | 66 | 1.1 (0.7–1.8) | 0.64 |
| P-trend | 0.0008 | 0.39 | ||||
| P-heterogeneity (coal type)b | 0.16 | <0.0001 | ||||
| Lifetime and exclusive smoky coal users | ||||||
| ≤28 ton-years | 5 | 1.0 (ref) | 56 | 1.0 (ref) | ||
| 29–64 ton-years | 19 | 3.0 (1.1–8.0) | 0.03 | 97 | 1.1 (0.8–1.7) | 0.52 |
| >64 ton-years | 35 | 3.6 (1.1–11.8) | 0.03 | 90 | 0.9 (0.5–1.5) | 0.65 |
| >64–85 ton-years | 20 | 3.8 (1.2–12.1) | 0.02 | 47 | 0.9 (0.5–1.6) | 0.75 |
| >85 ton-years | 15 | 2.7 (0.7–10.4) | 0.16 | 43 | 0.8 (0.4–1.4) | 0.44 |
| P-trend | 0.13 | 0.54 | ||||
| Lifetime and exclusive smokeless coal users | ||||||
| ≤28 ton-years | 5 | 1.0 (ref) | 18 | 1.0 (ref) | ||
| 29–64 ton-years | 8 | 2.1 (0.5–9.3) | 0.32 | 33 | 1.4 (0.7–2.8) | 0.37 |
| >64 ton-years | 21 | 6.5 (1.5–28.3) | 0.01 | 38 | 1.8 (0.8–3.9) | 0.13 |
| >64–85 ton-years | 6 | 4.3 (0.8–22.7) | 0.08 | 19 | 1.9 (0.8–4.2) | 0.14 |
| >85 ton-years | 15 | 9.8 (2.1–45.8) | 0.004 | 19 | 1.7 (0.8–4.0) | 0.19 |
| P-trend | 0.003 | 0.11 |
Adjusted for education (categorical variable no formal school vs any formal school), birth cohort [categorical six-level variable: 1917–21 (ref.), 1922–26, 1927–31, 1932–36, 1937–41, 1942–46, 1947–51], use of a portable stove or stove with chimney (time-dependent variable categorized as ‘1’ for ages when either stove type was used), cumulative years of cooking (<20, 20–40, >40 years), average number of hours spent indoors doing activities other than sleeping (continuous time-dependent variable), average number of rooms in home during lifetime (continuous time-dependent), average number of people in home during lifetime (continuous time-dependent), follow-up period (retrospective or prospective follow-up) and age.
P-heterogeneity calculated including cross-product terms (cumulative coal use x coal type) in models that only included lifetime and exclusive users of smoky and smokeless coal users.