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

University of Ottawa

Status: Enrolling

Conditions: Physiological Stress; Heat Stress

Treatments: Other: Simulated indoor temperature upper limit

Study type: Interventional

Funder types: Other

Identifiers

NCT07189507

HEPRU-2025-09-A

Details and patient eligibility

About

While an upper limit of 26°C has been shown to be protective for heat-vulnerable older occupants (DOI: 10.1289/EHP11651), 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. To safeguard the health of older adults, health agencies worldwide recommend the remain in 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 may not take appropriate countermeasures to mitigate physiological strain from indoor overheating. This may include overdressing 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. Further, 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 hot weather.

To address these important considerations, 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, shorts and socks), B) perform light exercise (stepping exercise to simulate activities of daily living, 4-4.5 METS) every hour (except during lunch hour period) dressed in light clothing, C) perform light exercise (4-4.5 METS) every hour (except during lunch hour period) dressed in light clothing (t-shirt, shorts and socks) and an added clothing layer (sweatshirt and sweatpants) and D) perform seated rest dressed in light clothing (t-shirt, shorts and socks) and an added clothing layer (sweatshirt and sweatpants). 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.

Enrollment: 10 estimated patients

Sex: All

Ages: 65 to 85 years old

Volunteers: Accepts Healthy Volunteers

Inclusion criteria

• Non-smoking.
• English or French speaking.
• Ability to provide informed consent.
• with or without a) chronic hypertension (elevated resting blood pressure; as defined by Heart and Stroke Canada and Hypertension Canada), b) type 2 diabetes as defined by Diabetes Canada, with at least 5 years having elapsed since time of diagnosis

Exclusion criteria

• Episode(s) of severe hypoglycemia (requiring the assistance of another person) within the previous year, or inability to sense hypoglycemia (hypoglycemia unawareness).
• Serious complications related to your diabetes (gastroparesis, renal disease, uncontrolled hypertension, severe autonomic neuropathy).
• Uncontrolled hypertension - BP >150 mmHg systolic or >95 mmHg diastolic in a sitting position.
• Restrictions in physical activity due to disease (e.g. intermittent claudication, renal impairment, active proliferative retinopathy, unstable cardiac or pulmonary disease, disabling stroke, severe arthritis, etc.).
• Use of or changes in medication judged by the patient or investigators to make participation in this study inadvisable.
• Cardiac abnormalities identified during screening

Trial design

Primary purpose: Basic Science

Allocation: Randomized

Interventional model: Crossover Assignment

Masking: Single Blind

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10 participants in 4 patient groups

Exposure to indoor temperature upper limit without physical activity and added clothing.

Experimental group

Description:

Participants, dressed in light clothing (t-shirt, shorts and socks), perform seated rest while exposed daylong (8 hours) to an indoor temperature maintained at 26°C and 45% relative humidity (humidex equivalent of 29).

Treatment:

Other: Simulated indoor temperature upper limit

Exposure to indoor temperature upper limit with physical activity.

Experimental group

Description:

Participants, dressed in light clothing (t-shirt, shorts and socks), perform light exercise (i.e., stepping, representing activities of daily living, 4-4.5 METS) every hour (except during lunch hour period) while exposed daylong (8 hours) to an indoor temperature maintained at 26°C and 45% relative humidity (humidex equivalent of 29).

Treatment:

Other: Simulated indoor temperature upper limit

Exposure to indoor temperature upper limit with added clothing.

Experimental group

Description:

Participants, dressed in light clothing (t-shirt, shorts and socks) and an added clothing layer (sweatshirt and sweatpants), perform seated rest while exposed daylong (8 hours) to an indoor temperature maintained at 26°C and 45% relative humidity (humidex equivalent of 29).

Treatment:

Other: Simulated indoor temperature upper limit

Exposure to indoor temperature upper limit with physical activity and added clothing.

Experimental group

Description:

Participants, dressed in light clothing (t-shirt, shorts and socks) and an added clothing layer (sweat shirt and sweat pants), perform light exercise (i.e., stepping, representing activities of daily living, 4-4.5 METS) every hour (except during lunch hour period) while exposed daylong (8 hours) to an indoor temperature maintained at 26°C and 45% relative humidity (humidex equivalent of 29).

Treatment:

Other: Simulated indoor temperature upper limit