Researchers led by investigators at Mass General Brigham have discovered that over the last 25 years, heat and cold-related deaths have caused more than 69,000 deaths in the U.S., disproportionately affecting certain populations. The findings are published in the Annals of Internal Medicine.

“Prior research, many of which was ecological, modeling or forecasting in nature, has examined heat- and cold-related deaths separately, but this study provides a real, observed nationwide and contemporary assessment of deaths related to non-optimal temperatures at both ends of the spectrum and across key demographic subgroups,” said senior author Shady Abohashem, MD, MPH, investigator at the Cardiovascular Imaging Research Center of Massachusetts General Hospital and Mass General Brigham Heart and Vascular Institute. Abohashem is also an instructor at Harvard Medical School.

For their study, Abohashem and his colleagues analyzed data from the Centers for Disease Control and Prevention’s WONDER (Wide-ranging Online Data for Epidemiologic Research) platform, specifically looking for death certificates that recorded temperature as a contributing or underlying cause of death based on codes from medical records.

Between 1999 and 2024, there were 69,713,971 U.S. deaths, of which 69,256 (one out of every 1,000) had extreme temperature exposure recorded as an underlying or contributing cause (35% heat-related and 65% cold-related). Crude estimates indicated that temperature-related mortality rates were higher in more recent years.

“Our findings show that both heat and cold exposure continue to claim thousands of lives every year in the United States, deaths that are largely preventable,” said Abohashem.

“While most temperature-related deaths are still driven by cold exposure, heat-related deaths are expected to rise as climate change accelerates.”

Older adults (≥65 years) and males had higher temperature-related mortality compared with their counterparts. Regarding race/ethnicity, Black individuals had the highest heat-related adjusted mortality rates, which were more than twice those of white individuals. Cold-related adjusted mortality rates were likewise greatest for Blacks, followed by Whites and Hispanics.

“Climate change increases risks of severe weather events, and our findings underscore the need for targeted adaptation strategies, like improving housing quality, access to cooling and heating, and early-warning systems, to protect vulnerable groups as climate extremes intensify,” said Abohashem.

“The results help us understand which populations may be disproportionately affected so public health strategies can shift accordingly.”