TL;DR
Get self-care and calm essentials delivered free — and shop member deals
- Fast, free delivery on millions of items
- Access to Prime Big Deal Days deals on October 6–7
- Prime Video, Amazon Music and more included
In a controlled trial of 18 adults ages 67 to 84, repeated indoor heat exposure was linked to physiological strain that did not fully resolve overnight, even when the room cooled to 26°C. The researchers say the findings support keeping indoor temperatures at or below that level during heat events, while cautioning it does not guarantee protection for every older adult.
A controlled University of Ottawa trial found that some signs of heat-related strain persisted overnight in older adults after repeated hot days indoors, despite the room cooling to 26°C (79°F). The findings, published in The Lancet Planetary Health, suggest that nighttime cooling alone may not fully offset the effects of daytime overheating during a multiday heat wave.
The study followed 18 adults ages 67 to 84 from the Ottawa–Gatineau region, with equal numbers of women and men. Participants spent three consecutive days and two nights in a studio apartment-style climate chamber at the University of Ottawa. In the heat-wave session, the chamber was held at 34°C (93°F) by day and cooled to 26°C overnight. A separate comparison session kept it at 26°C throughout both day and night.
During the hot-day conditions, participants’ peak core temperature averaged 37.8°C (100.0°F), compared with 37.4°C (99.3°F) during the cooler comparison. Their heart rates averaged five beats per minute higher. Researchers also reported higher blood markers associated with kidney and gastrointestinal stress, lower blood pressure and cardiac autonomic function, and small declines in balance and cognitive test performance.
Most measured physiological responses moved back toward baseline overnight, but recovery was incomplete. Lower morning systolic blood pressure and elevated kidney-stress markers remained evident the following mornings. No adverse events were reported. The researchers said participants’ core temperatures did not keep rising from one day to the next, even as other measures indicated ongoing strain.
Why Daytime Cooling Matters
The results matter because indoor shelter does not necessarily mean protection from heat when a home stays hot. Many Canadian homes lack air conditioning, and indoor temperatures can remain elevated during prolonged extreme heat. Older adults may therefore experience repeated heat exposure even without going outdoors.
The researchers say maintaining an indoor temperature of 26°C or lower throughout the day and night can substantially reduce physiological strain in older adults. That temperature is an upper limit intended to reduce risk, not a guarantee that every person will be safe. The study also cautions against relying on core temperature alone: a stable reading did not mean all measured effects had resolved.
The trial measured physiological and functional responses under controlled conditions; it did not establish how often these changes lead to illness in everyday settings. Its small sample also means the results should be interpreted as evidence about responses in this group, rather than a precise estimate of risk for all older adults.
portable air conditioner for elderly
As an affiliate, we earn on qualifying purchases.
As an affiliate, we earn on qualifying purchases.
From One Hot Day to Three
The study builds on earlier work by the University of Ottawa research team examining a single day of heat exposure. Health Canada issued guidance in June 2026 recommending an upper indoor temperature limit of 26°C for older adults during extreme heat, informed in part by that earlier research. The new trial examined repeated daytime exposure alongside overnight recovery.
Lead researcher Glen Kenny, a professor in the university’s Faculty of Health Sciences and director of its Human and Environmental Physiology Research Unit, said laboratory simulations allow researchers to study heat exposure and assess possible cooling strategies. The study’s day and night temperatures were selected to reflect indoor conditions recorded during heat events in Canada and the United States, according to the report.
The trial was a single-site randomized crossover study: participants took part in both the hot and cooler conditions, allowing researchers to compare responses within the same group. Its findings appeared in The Lancet Planetary Health in 2026. The supplied publication information identifies the paper as “Effects of a 3-day simulated heatwave on physiological and functional outcomes in older adults in Canada.”
“Physiological strain persisted across each day of the heat wave, and some effects did not fully resolve overnight, even when the apartment cooled to 26°C (79°F).”
— Glen Kenny, University of Ottawa professor and study researcher
Limits of the Trial Findings
The trial included 18 participants at one research site, so it cannot establish how broadly the measured effects apply to older adults with different health conditions, living arrangements or access to cooling. The supplied report does not give detailed results for individual participants or specify how the observed changes relate to the risk of clinical illness.
The researchers observed physiological responses under simulated conditions, not the full range of circumstances people face during heat waves. It remains unclear how long the residual morning changes last beyond the two overnight recovery periods studied, or whether different cooling patterns would produce different outcomes. The study also reported no adverse events, but that does not establish that all forms or durations of indoor heat exposure are safe.
Applying the Temperature Guidance
The study adds evidence to the case for keeping indoor temperatures at or below 26°C during sustained heat events, consistent with Health Canada’s June 2026 guidance for older adults. The researchers say further work using heat simulations can help evaluate how indoor cooling strategies affect vulnerable groups.
The report does not announce a new trial or a change to the guidance. For now, the main practical point from the researchers is that cooling only overnight may not fully reverse strain after hot days. The effects of other cooling approaches, and how the study’s measurements translate into health outcomes outside the laboratory, remain subjects for further research.
Key Questions
What did the University of Ottawa study find?
In a controlled trial, some physiological signs of strain remained the morning after older adults experienced repeated hot days indoors, even after the chamber cooled overnight to 26°C (79°F).
How many people took part?
The trial involved 18 adults ages 67 to 84 from the Ottawa–Gatineau region, with equal numbers of women and men.
What temperatures did researchers simulate?
In the heat-wave condition, the apartment-style chamber was set to 34°C (93°F) during the day and 26°C overnight. In the comparison condition, it stayed at 26°C day and night.
Does 26°C guarantee protection from heat?
No. The study’s lead researcher described 26°C as an upper indoor limit intended to reduce heat-related risk, not a guarantee of protection for every older adult.
Did participants’ body temperatures rise each day?
No. Researchers said core body temperature did not worsen day over day, but lower morning systolic blood pressure and elevated kidney-stress markers persisted. They cautioned that core temperature alone does not capture all signs of physiological strain.
Source: rss
Fall Picks
fall essentials
As an affiliate, we earn on qualifying purchases.
