A range of convincing data shows correlations between the presence of airborne particulates, such as those in wood smoke, and raised late-life mortality due to cardiovascular disease and respiratory disease. The likely mediating mechanism is an increased burden of chronic inflammation, due to the effects of particulates on lung tissue. The challenge in any such study is the associated correlation between wealth and air quality: wealthier people do not tend to use wood stoves for cooking, or live in more heavily polluted areas, but it is also the case that wealthier people tend to live longer for many reasons.
Some natural experiments allow the correlations between wealth and health and between particulate air pollution and health to be better distinguished. For example, the Puget Sound area has quite varied levels of airborne particulates and there is localized data on pollution and health going back decades. Other examples can be found in Asia, where happenstance has led to populations with similar socioeconomic circumstances exposed to different sources and degrees of particulate air pollution.
Long-term exposure to household air pollution (HAP) is a public health problem worldwide and is among the top 10 hazard factors for disease. Solid fuel is the largest source of HAP worldwide, where nearly a third of the population in low- and middle-income countries (LMICs) rely on it for primary domestic cooking, heating, or lighting energy. Notably, exposure to air pollution from solid fuel burning may directly or indirectly contribute to over 4 million deaths and 110 million disabilities annually.
The association of solid fuel use and common diseases has been proved in many studies on the elderly. Owing to physical limitations and social factors, the elderly are generally most active in and around the house, and they willingly perform housework and spend more time on it as they age. A cohort study indicated that the use of biomass fuel is associated with higher hazard ratios (HRs) of hypertension among the elderly (aged ≥65 years). The Chinese Longitudinal Healthy Longevity Survey (CLHLS) is an open, prospective, and national cohort of community-dwelling Chinese aged 65 years. In this study, we investigated whether the type of fuel used for cooking is associated with subsequent 8-year mortality and whether switching the fuel used for cooking for 4 years is associated with changes in HR with successive 5 years of follow-up.
Among the participants in the 2011-2018 survey, 53% reported using solid fuel. Such group was associated with a 9% increase in mortality risk relative to clean fuel users (HR = 1.09). Among participants in the 2014-2018 survey, 339 reported a switch from solid to clean fuels and they were not at increased mortality risk relative to the 488 people that reported a stable use of clean fuels (HR = 1.14) although the estimated HR was similar to the one for stable solid fuel users (HR = 1.19). Interaction and stratified analyses showed that solid fuel use had an impact on mortality in participants who were non-current smokers, had low dietary diversity scores, and were living in areas with high PM2.5 concentrations (over 50 μg/m3) and city population below 8 million. These findings showed a clear association between solid fuel use and mortality among older Chinese, and an even stronger association between risk of mortality and solid fuel use among individuals exposed to high levels of PM2.5.