A Longitudinal Study on the Impact of Indoor Temperature on Proximal Heat-Related Symptoms in Older Adults Living in Non-Air-Conditioned Households

Abstract

BACKGROUND AND AIM: Heat waves result in a significant health burden, causing particular concern for at-risk populations such as older adults. Outdoor temperatures are often assessed as the exposure of interest and are used for heat warning systems despite individuals spending most of their time indoors. Additionally, many studies utilize ecological designs, where death or hospitalizations are the studied outcomes. Proximal outcomes should also be assessed to better understand early symptoms for refining prevention efforts. In this study, we assessed the relationship between indoor temperature and proximal symptoms in individuals 60 years and older living in non-air-conditioned households in Montérégie, Quebec during the 2017-2018 summer months. METHODS: We recruited 277 participants and gathered continuously measured temperature and humidity data from nearable sensors and health-related questionnaires administered by health professionals across three periods of increasing outdoor temperatures, where the reference measurement (T1) occurred during a cool period with a target temperature of 18ºC-22ºC and two measurements (T2 and T3) occurred during warmer periods with a target temperature of 28ºC-30ºC and 30ºC-33ºC, respectively. We collected information on stress, fatigue and other heat-related symptoms. We used Generalized Estimating Equations with Poisson regression models to estimate risk ratios for the relationship between temperature and heat-related symptoms. RESULTS:We found that higher indoor temperatures increased the risk of dry mouth, fatigue, thirst, more frequent urination, and dark urine as well as trouble sleeping compared to the reference cool-period. With the exception of dark urine and depression, we identified a non-linear relationship with identified thresholds varying across symptoms of interest. CONCLUSIONS:This study identified that increasing indoor temperatures are an etiologic factor in the development of these proximal symptoms. By considering the prevalence of these early-stage outcomes and indoor temperature exposures, adaptation strategies may be improved to minimize the burden of heat among vulnerable communities. KEYWORDS: Environmental epidemiology, temperature, temperature extremes