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

Not Applicable

Not yet recruiting

• Conditions: Heat Stress; Physiological Stress

• Registration Number: NCT07189507
• Lead Sponsor: University of Ottawa

Brief Summary

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.

Detailed Description

Not available

Study Timeline

• Status Verified: 2025-09
• Study Start: 2025-09-01
• Study First Submitted: 2025-09-16
• Study First Submitted QC: 2025-09-16
• Last Update Submitted: 2025-09-16
• Study First Posted: 2025-09-24
• Last Update Posted: 2025-09-24
• Primary Completion: 2026-09-30
• Study Completion: 2027-03-31

Recruitment & Eligibility

• Status: NOT_YET_RECRUITING
• Sex: All
• Target Recruitment: 10

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

Study & Design

• Study Type: INTERVENTIONAL
• Study Design: CROSSOVER

Primary Outcome Measures

Name	Time	Method
Core temperature (Peak) during daylong exposure to indoor temperature limit.	End of 8 hour daylong exposure	Peak rectal temperature (15 min average) during exposure. Rectal temperature is measured continuously throughout the 8 hour exposure to the simulated indoor temperature upper limit.
Core temperature (AUC) during daylong exposure to indoor temperature limit.	End of 8 hour daylong exposure	Areas under the curve (AUC) of rectal temperature during the 8 hour exposure to the simulate indoor temperature upper limit.
Core temperature end of daylong exposure to indoor temperature limit.	End of 8 hour daylong exposure	Rectal temperature measured at hour 8 of exposure to indoor temperature limit (15-min average).
Heat rate (Peak) during daylong exposure to indoor temperature limit.	End of 8 hour daylong exposure	Peak heart rate (15 min average) during exposure. Heart rate is measured continuously throughout the 8 hour exposure to the simulated indoor temperature upper limit.
Heart rate (AUC) during daylong exposure to indoor temperature limit.	End of 8 hour daylong exposure	Areas under the curve (AUC) of heart rate during the 8 hour exposure to the simulate indoor temperature upper limit.
Heart rate variability: RMSSD during daylong exposure to indoor temperature limit.	At the start (hour 0) and end of 8 hour daylong exposure	Root mean squared standard deviation of normal-to-normal R-wave to R-wave intervals (RMSSD) measured during 5 minutes of paced breathing (15 breaths/min) with participants in the supine position. RMSSD will be evaluated twice, during two paced breathing periods (separated by 4 min of supine rest).
Heart rate variability: SDNN during daylong exposure to indoor temperature limit.	At the start (hour 0) and end of 8 hour daylong exposure	Standard deviation of normal-to-normal R-wave to R-wave intervals (SDNN) measured during 5 minutes of paced breathing (15 breaths/min) with participants in the supine position. SDNN will be evaluated twice, during two paced breathing periods (separated by 4 min of supine rest).
Cardiac response to standing from supine (30:15 ratio) during daylong exposure to indoor temperature limit.	At the start (hour 0) and end of 8 hour daylong exposure	Cardiac response to standing evaluated as the ratio between the highest R-wave to R-wave interval (lowest heart rate) measured at the 30th heart beat after standing from supine (+/- 5 beats) and the lowest R-wave to R-wave interval (highest heart rate) measured at the 15th heart beat after standing (+/- 5 beats). Cardiac response to standing will be evaluated twice, during two lying-to-standing tests (separated by 10 min of supine rest).
Systolic response to standing from supine during daylong exposure to indoor temperature limit.	At the start (hour 0) and end of 8 hour daylong exposure	Systolic blood pressure response to standing evaluated as the difference in blood pressure measured between the standing and supine. Standing systolic blood pressure will be taken as the lowest value of those measured after 60 and 120 seconds of standing. Systolic response to standing will be evaluated twice, during two lying-to-standing tests (separated by 10 min of supine rest).
Systolic blood pressure during daylong exposure to indoor temperature limit.	At the start (hour 0) and end of 8 hour daylong exposure	Systolic blood pressure measured in triplicate via automated oscillometry (\~60 seconds between measures).
Diastolic blood pressure during daylong exposure to indoor temperature limit.	At the start (hour 0) and end of 8 hour daylong exposure	Diastolic blood pressure measured in triplicate via automated oscillometry (\~60 seconds between measures).
Rate pressure product during daylong exposure to indoor temperature limit.	At the start (hour 0) and end of 8 hour daylong exposure	Rate pressure product, an index of myocardial work and strain, calculated as systolic blood pressure x heart rate.
Reaction time during daylong exposure to indoor temperature limit (cognitive function).	At the start (hour 0) and end of 8 hour daylong exposure	Participants will be provided with a tablet device with the Sway Medical testing platform for the assessment of reaction time. Participants will be asked to initiate a movement of the device in response to a visual cue.
Impulse control during daylong exposure to indoor temperature limit (cognitive function).	At the start (hour 0) and end of 8 hour daylong exposure	Participants will be provided with a tablet device with the Sway Medical testing platform for the assessment of impulse control. Participants will be asked to respond to both "go" and "no-go" visual cues. In response to the "go" cue, participants will initiate a movement of the device.
Executive function during daylong exposure to indoor temperature limit (cognitive function).	At the start (hour 0) and end of 8 hour daylong exposure	Participants will be provided with a tablet device with the Sway Medical testing platform for the assessment of executive function. Participants will complete the Cued Stroop test, in which they are presented a sequence of congruent, neutral and incongruent colour-word tasks.
Memory recall during daylong exposure to indoor temperature limit (cognitive function).	At the start (hour 0) and end of 8 hour daylong exposure	Participants will be provided with a tablet device with the Sway Medical testing platform for the assessment of memory recall. Participants complete both a delayed recall test and a working memory test.
CDC 4-Stage Balance Test during daylong exposure to indoor temperature limit (postural stability).	At the start (hour 0) and end of 8 hour daylong exposure	To assess postural stability, participants hold a tablet to their chest, then auditory cues guide participants through four consecutive stances, feet side by side, instep of one foot touching the big toe of the other foot, tandem stand with one foot in front of the other, heel touching toe, and stand on one foot. The balance assessment will be evaluated based on movement detected by an accelerometer integrated into the hardware of the tablet device (Sway Medical Inc).
BTrackS Balance Assessment during daylong exposure to indoor temperature limit (postural stability).	At the start (hour 0) and end of 8 hour daylong exposure	To assess postural stability, participants will be asked to stand on a BTracks force plate with their feet spread out to shoulder width, hand on their hips and eyes closed. The assessment will comprise of four trials (one practice trial) lasting 20 seconds in length and 20 seconds between trials. Center of pressure (COP) vector data along vertical (y) and horizontal (x) axes will be summed for the total path excursion length (cm) during each trial.
Fluid consumption during daylong exposure to indoor temperature limit.	At end of 8 hour daylong exposure	Average hourly fluid consumption calculated by weighing participant water intake at the start and end of each hour of exposure (normalized to the exposure duration).
Fluid loss during daylong exposure to indoor temperature limit.	At end of 8 hour daylong exposure	Fluid loss calculated as the change in body mass during each exposure presented as a percentage of baseline body mass (corrected for food consumption).
Change in plasma volume during daylong exposure to indoor temperature limit.	At end of 8 hour daylong exposure.	Change in plasma volume from baseline values calculated from duplicate measurements of hemoglobin and hematocrit at the start and end of each exposure using the technique by Dill and Costill.
Thermal comfort scale during daylong exposure to indoor temperature limit.	At the start (hour 0) and end of 8 hour daylong exposure	Thermal comfort assessed via a visual analog scale ("How comfortable does your body temperature feel?") ranging from "extremely uncomfortable" to "extremely comfortable"(midpoint: neutral).
Thirst sensation scale during daylong exposure to indoor temperature limit.	At the start (hour 0) and end of 8 hour daylong exposure	Thermal sensation assessed via a visual analog scale ranging from extremely hot to neutral (midpoint: hot).
Arousal scale during daylong exposure to indoor temperature limit.	At the start (hour 0) and end of 8 hour daylong exposure	Felt arousal scale assessed via a visual analog scale ("How worked up are you?") ranging from "high arousal" to "low arousal".
Thermal sensation scale during daylong exposure to indoor temperature limit.	At the start (hour 0) and end of 8 hour daylong exposure	Thermal sensation assessed via a visual analog scale ("How hot do you feel?") ranging from "extremely hot" to "neutral"(midpoint: hot)
Orthostatic intolerance symptoms assessment during daylong exposure to indoor temperature limit.	At end of 8 hour daylong exposure.	Cumulative sum of scores on 6 questions asking participant to rank symptoms associated with orthostatic intolerance during the lying to standing tests. All symptoms scored on a scale from 0 (none) to 10 (worst possible) and include feelings of: (1) "dizziness, lightheadedness, feeling faint, or feeling like you might black out"; (2) "Problems with vision (blurring, seeing spots, tunnel vision, etc.)"; (3) "Weakness"; (4) "Fatigue"; (5) "Trouble concentrating"; and (6) "Head and neck discomfort".

Secondary Outcome Measures

Name	Time	Method
Profiles of Mood States (POMS) during daylong exposure to indoor temperature limit.	At the start (hour 0) and end of 8 hour daylong exposure	Potential changes in mood (7 subscales of mood: tension, anger, depression, fatigue, confusion, vigor and esteem related affect). The POMS-40 is a validated, self-administered questionnaire that examines seven distinct aspects of mood state across two positive subscales (Esteem-Related Affect, and Vigor) and five negative subscales (Fatigue, Tension, Confusion, Anger, and Depression), which are described across 40 distinct adjectives. For each individual item, participants were asked to describe "how you feel right now" by responding using a 5-point Likert scale (0 = "Not at all", 1 = "A little", 2 = "Moderately", 3 = "Quite a lot", or 4 = "Extremely"). The values of items associated with a specific subscale (e.g., Fatigue) were summed to calculate its score.
Environmental Symptoms Questionnaire (ESQ) during daylong exposure to indoor temperature limit.	At the start (hour 0) and end of 8 hour daylong exposure	Self-reported environmental reactions and medical symptomatology associated with prolonged heat exposure. The ESQ-IV is a validated 68-item, self-administered questionnaire that has been used successfully in identifying symptomatology during exposure to a wide variety of environmental conditions, including heat exposure \[24, 25\].; Participants are asked to assess and described "how you have been feeling today" by responding to each item using a 6-point Likert scale (0 = "Not at all", 1 = "Slight", 2 = "Somewhat", 3 = "Moderate", 4 = "Quite a bit", or 5 = "Extreme"). Total Symptom Score was calculated from this data by taking the sum of the intensity ratings from all 68 individual items using reverse scores for the three positive items from the list ("I Felt Good", "I Felt Alert", and "I Felt Wide Awake").
Sleepiness during daylong exposure to indoor temperature limit A.	At the start (hour 0) and end of 8 hour daylong exposure	Karolinska sleepiness scale measures the subjective level of sleepiness at a particular time.
Sleepiness during daylong exposure to indoor temperature limit B.	At the start (hour 0) and end of 8 hour daylong exposure	Stanford sleepiness scale consists of only one item, where participant must identify one of seven statements that best represents their level of perceived sleepiness. It employs a scale of 1 to 7 with 1 = feeling wide awake and 7 = sleep onset soon.
Sleep quality and quantify assessment during daylong exposure to indoor temperature limit.	At end of 8 hour daylong exposure.	The following questionnaires will be administered: Consensus Sleep Diary (CSD) to provide an overview of the sleep quantity and quality of the previous night.; Richards-Campbell Sleep Questionnaire to evaluate the perception of sleep . Leeds Sleep evaluation questionnaire which is 10-item, subjective, questionnaire designed to assess changes in sleep quality over the course of the intervention.

Trial Locations

Locations (1)

University of Ottawa; 🇨🇦 Ottawa, Ontario, Canada