TOPLINE:

During extreme heat, deaths were more likely in nursing homes without air conditioning (AC) than in those with it, and modeling suggested that air conditioner installations averted deaths on extremely hot days after the mandate was announced in 2020.

METHODOLOGY:

• Researchers conducted a case-crossover study to compare the risk for mortality on extremely hot days using data on deaths in nursing homes with and without AC in Ontario, Canada.
• For the warm months (June-September) from 2010 to 2023, extremely hot days were defined as the hottest 10% of days for each nursing home, based on a heat index combining temperature and humidity.
• AC status for each death was defined by whether the nursing home had AC during the 28 days preceding and including the date of death.
• The final analysis included 40,255 deaths in nursing homes with AC (mean age of residents, 87.2 years; 64.8% women) and 33,323 deaths in those without AC (mean age of residents, 86.8 years; 65.6% women).

TAKEAWAY:

• Extreme heat was linked to higher likelihood of mortality in nursing homes without AC (odds ratio [OR], 1.11; 95% CI, 1.06-1.16), whereas the association was not statistically significant in nursing homes with AC.
• The relative odds of mortality were higher in nursing homes without AC than in those with AC (relative OR, 1.08; 95% CI, 1.01-1.15).
• The effects of extreme heat on the risk for mortality persisted for up to 3 days after initial exposure.
• As per modeling estimates, installing air conditioners in 336 nursing homes after 2020 averted about 33 deaths on extremely hot days. Installing ACs in 2010 would have prevented about 131 such deaths.

IN PRACTICE:

“Given the growing frequency, intensity, and duration of extreme heat events due to climate change, our findings underscore the need for universal access to AC in nursing homes,” the authors of the study wrote. “Physicians can also support residents with preventive measures, such as maintaining hydration, wearing lighter clothing, and staying indoors,” they added.

SOURCE:

This study was led by Gabrielle M. Katz, BHSc, of University of Toronto, Toronto, Ontario, Canada. It was published online on December 15, 2025, in JAMA Internal Medicine.

LIMITATIONS:

This study treated extreme heat as a simple yes or no, which limited analysis of death risk as the dose of heat increased. Despite steps to classify heat exposure more accurately, some exposures may have been misclassified. Data on race of residents was not available.

DISCLOSURES:

No specific source of funding was reported for this study. The authors reported having no conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.