Inflammatory markers, lung function, and respiratory events in relation to indoor and ambient air pollution

BACKGROUND AND AIM: Ambient air pollution causes a range of adverse health effects, whereas effects of indoor sources of air pollution are not well described in high-income countries. We compared hazards of ambient air pollution and indoor combustion sources with respect to respiratory events and preceding lung function and inflammatory response in the blood in a middle-aged Danish cohort. METHODS: Our cohort comprised 4,812 men and women aged 49 to 63 years at the recruitment in 2009-11, with information on exposure to second-hand smoke (SHS) and use of candles and wood stove, as well relevant covariates. Ambient air pollution exposure was assessed as 2-year mean nitrogen dioxide (NO2) at the address. Lung function was assessed as % predicted forced expiratory volume in the first second (FEV1) and inflammatory markers comprised interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) at baseline. We followed the cohort up for the first hospital contact for respiratory events [asthma, chronic obstructive pulmonary disease (COPD), pneumonia] until 2018. We used regression and Cox proportional hazard models for biomarkers and respiratory events, respectively, associated with indoor and ambient air pollution exposure after controlling for potential confounders. RESULTS: We observed a decrease in FEV1 and increased IL-6 and TNF-α associated with exposure to SHS and NO2, but not with use of candles or wood burning. Respiratory events, including COPD incidence, showed positive associations with SHS, but not with other indoor combustion sources (candle use or wood burning) or ambient air pollution. CONCLUSIONS: These results suggest that the levels of exposure to SHS and ambient air pollution are more harmful for lung function and inflammatory response in the blood than the levels of exposure to indoor combustion sources from candles and wood stoves in a high-income setting. Keywords Ambient air pollution, indoor air pollution, inflammation, lung function, second-hand smoke