Suitability of the 26 °C Indoor Temperature Upper Limit for Older Adults: Impacts of Clothing and Daily Activity

While an upper limit of 26°C has been shown to be protective for heat-vulnerable older occupants (Environ Health Perspect 131(6): 67003 (2023)), this recommendation did not consider the added heat burden associated with increases in internal heat production accompanying activities of daily living or the restriction to heat loss caused by clothing insulation. A key recommendation by many health agencies worldwide to prevent heat-related illnesses in older adults is to \"stay cool during hot weather for example, stay in a cool space indoors, avoid strenuous activity, wear lightweight clothing, and drink cool water regularly throughout the day\". However, older adults do not sense heat as well as their younger counterparts. Consequently, they are likely to overdress despite high indoor temperatures. In other cases, individuals may wear insulated clothing in hot weather to observe cultural or religious modesty requirements, which serve as expressions of faith and identity rather than a tool for thermoregulation. Moreover, many individuals may be unaware of the consequences of increases in physical activity on heat gain and may therefore not adjust their normal day-to-day activity levels to prevent potentially dangerous rises in body temperature. Consequently, this may necessitate a lowering of recommended upper indoor temperature limit during an hot weather or an extreme heat event. On separate occasions, the investigators will assess the change in body temperature and cardiovascular strain in older adults (65-85 years) exposed for 8 hours to the recommended indoor temperature upper limit of 26°C and 45% relative humidity equivalent humidex of 29 (considered comfortable) while they A) perform seated rest dressed in light clothing (t-shirt and shorts), B) perform light exercise (stepping. to simulate activities of daily living) every hour dressed in light clothing, C) perform light exercise dressed in light clothing (t-shirt and shorts) and an added clothing layer (sweat shirt, sweat pants and socks) and D) perform seated rest dressed in light clothing (t-shirt and shorts) and an added clothing layer (sweat shirt, sweat pants and socks). With this experimental design, investigators will assess the effects of added clothing insulation and light activity, representative in activities of daily living on physiological strain and identify whether refinements in the recommended 26°C indoor temperature limit may be required.