TABLE 4.

Estimated proportions of associations between particulate matter <2.5 µm (PM_2.5) and nitrogen dioxide (NO₂)^# and all-cause mortality and incident cardiovascular disease (CVD), mediated by forced expiratory volume in 1 s (FEV₁)

	Coefficient¶ (95% CI)
	PM2.5	NO2
All-cause mortality
All	0.18 (0.02–0.33)	0.27 (0.03–0.51)
Never-smokers	0.16 (−0.05–0.38)	0.28 (−0.12–0.67)
Ever-smokers	0.15 (−0.05–0.35)	0.19 (−0.04–0.43)
All incident CVD
All	0.09 (0.04–0.13)	0.16 (0.06–0.25)
Never-smokers	0.11 (0.03–0.19)	0.20 (0.04–0.35)
Ever-smokers	0.06 (0.01–0.11)	0.10 (0.00–0.19)

^#: analyses not run for particulate matter <10 µm, since there was no strong evidence of association between this pollutant and mortality or incident CVD; ^¶: coefficients are estimate proportions of the effect of the pollutant on the outcome mediated via FEV₁. Results were produced using the med4way Stata package, specifying the lower and upper quartiles of the air pollutants as the referent (a0) and actual (a1) levels of the exposure (a0), the median of FEV₁ as the level of the mediator at which the four-way decomposition is computed (m), “cox” as the form of regression model for the outcome (yreg) and “linear” as the form of the regression model for the mediator (mreg). Confounders (c) were fixed at female sex, income <GBP 31 000, no qualifications, no passive smoke exposure, and at the means of height, body mass index and pack-years smoked.