Solid fuel-related indoor air pollution and poor sleep quality in the elderly: a national longitudinal study in China

Abstract

Background: Sleep disorders are a public health issue in an aging society. Outdoor air pollution has been linked to poor sleep quality, but few studies have investigated the relationship between indoor air pollution from solid fuel combustion and sleep quality in elderly. Objective: To evaluate the association between indoor air pollution due to cooking solid fuels and sleep quality among elderly in China. Methods: We analyzed data from CHARLS, a national survey of ~17,000 residents aged over 45 from 150 counties in China. Participants were restricted to those who completed waves of CHARLS in 2011, 2013, and 2015 (n=8,668). Sleep quality was indicated by self-reported average sleep duration (hours/night) and the numbers of restless days per week in the 2015 survey. Participants also reported household cooking fuel type in all three surveys. We compared the “solid fuels”, primarily coal and wood burning, with the “clean fuels” including electric, natural gas, and liquefied petroleum gas as the reference. Years of solid fuel use (0, 1-4 or ≥5 years) were evaluated. We used multinomial logistic regression to estimate the odd ratios (OR) and 95% confidence interval (CI) for sleep duration (7-9 hours/night as the reference) and restless sleep (0 day as the reference) according to fuel types adjusting for potential confounding factors.Results: Solid fuels use for 5 or more years was associated with a shorter duration of sleep (OR=1.17 95%CI 1.02, 1.35 for ≤6 hours/day) and higher frequencies of restless days of sleep (OR=1.30 95%CI 1.11, 1.52 for ≥5 days/week) compared with clean fuels users. The associations were smaller in magnitude for solid fuels use in 1-4 years. Conclusions: Primary cooking fuel was associated with poor sleep quality in an elderly Chinese population. Further research of the specific type of fuels and indoor air pollutants to inform intervention strategies.