Modeling Exposure-Mortality Relationships for Indoor Heat

Most individuals spend the majority of their time indoors. However, epidemiological evidence of the association between heat and mortality is dominated by studies using outdoor temperature as a proxy for personal exposure. To demonstrate how an exposure-response relationship between indoor heat and mortality may relate to that between outdoor heat and mortality, we develop a novel mathematical modeling approach. This approachuses the relationship between regional daily average indoor and outdoor temperature to map the exposure-response relationship for outdoor heat, estimated by epidemiological studies, to indoor heat. Due to the modifying effect of buildings on heat exposure, we show that a change in indoor temperature may be associated with a greater change in mortality than an equal change in outdoor temperature. This has implications for researchers seeking to assess the health impact of changes in indoor heat exposure. Furthermore, it provides a new theoretical  framework for interpreting potential differences in the temperature-mortality relationship of indoor and outdoor heat exposure in epidemiological studies.