Purpose: Cardiovascular disease and obstructive lung disease are leading global causes of death. Despite this, the impact of secondhand smoke (SHS) exposure on pulmonary function and cardiovascular disease remains uncertain. Our goal was to elucidate the association between baseline SHS exposure and the risk of lung function decline and cardiovascular mortality over a period of nearly a decade.
Methods: We used data from a longitudinal cohort study of 1,057 older adults to study the association between baseline SHS exposure and the risk of lung function decline and cardiovascular mortality. The effect of SHS exposure on cardiovascular mortality may be mediated by its influence on FEV1 and biological processes captured by measurement of FEV1. Alternatively, the effect of SHS may be mediated by baseline cardiovascular disease status, which reflects the combined effects of traditional cardiovascular risk factors. To correctly estimate the effect of SHS and FEV1 on cardiovascular mortality, we used marginal structural models (MSMs) that took into account the mediating effects of FEV1 and baseline cardiovascular disease in the causal pathway.
Results: In longitudinal multivariate analyses, lifetime cumulative home and work SHS exposure were associated with a greater decline of FEV1 (-15 mL/s; 95% CI, -29 to -1.3 mL/s and -41 mL/s; 95% CI, -55 to -28 mL/s per 10-year cumulative exposure, respectively). Lifetime home SHS exposure was associated with a greater risk of cardiovascular mortality in both conventional multivariate analysis (HR, 1.10 per 10 years of exposure; 95% CI, 0.99 to 1.24) and the MSM for FEV1 (HR, 1.06; 95% CI, 0.95 to 1.19) and baseline cardiovascular disease (HR for subjects with no baseline cardiovascular disease, 1.39; 95% CI, 1.17 to 1.66).
Conclusions: Lifetime SHS exposure appears to result in a greater decline in lung function and risk of cardiovascular mortality, taking into account confounders and the mediating effect of FEV1 and baseline cardiovascular disease.