Schizophrenia pinpointed as a key factor in heat deaths

On 25 June 2021, as a blanket of hot air descended on the Pacific Northwest, British Columbia’s provincial government issued a news release warning about the approaching heat wave’s dangers. The announcement drew attention to the elderly, children, people working or exercising outdoors, pets, and “people with emotional or mental health issues whose judgment may be impaired.”

Even so, more than 600 people died from the heat in British Columbia, as temperatures topped 40°C for days, shattering records in a region better known for temperatures usually half as high.

Now, new research has zeroed in on one of the hardest hit groups: people with schizophrenia. Epidemiologists combing through provincial health records found that, overall, those with mental health conditions seemed to have an elevated risk of a heat-related death. That was most severe for people with schizophrenia—a 200% increase compared with typical summers. “Those are really large numbers and … alarming,” says Peter Crank, a geographer at Oklahoma State University, Stillwater.

“We didn’t protect them,” laments Sarah Henderson, an environmental epidemiologist at the British Columbia Centre for Disease Control who oversaw the research, published on 15 March in the journal GeoHealth . “These results show that people with schizophrenia need extra protection, extra support, and extra care.”

Earlier research had shown schizophrenia can make people more vulnerable to heat. Crank, for instance, recently reported a link between higher temperatures and hospitalization of people with schizophrenia in Phoenix. But the connection “just hasn’t made it to the mainstream,” Henderson says.

To examine which chronic health problems put people at greater risk during the heat wave, Henderson and her team paired a detailed accounting of deaths in British Columbia with medical records in Canada’s national health care system. They compared the medical histories of 1614 people who died during the 8-day heat wave with 6524 deaths on the same dates during the prior 9 years. The data covered 26 medical conditions, from heart disease to dementia to osteoporosis.

Henderson expected the data to confirm the widespread belief that kidney disease and heart disease are key risk factors during extreme heat. The records did show people with coronary artery disease were 18% more likely to die during the 2021 heat wave than in previous years, and those with kidney disease were 36% more likely to die. But the increase in schizophrenia deaths dwarfed both those conditions.

Overall, more than 8% of the people who died during the hot week had a history of schizophrenia, compared with 2.7% in the same week during a typical year. The results were even more striking for a subset of the total deaths—the 280 that the provincial coroner’s service certified as being heat related. Thirty-seven people who died—more than 13%—had schizophrenia.

The death toll isn’t a surprise to George Keepers, a psychiatrist and schizophrenia specialist at Oregon Health and Science University who wasn’t involved in the study. “There’s a whole host of things that people with this very unfortunate illness are vulnerable to,” Keepers says.

For instance, schizophrenia can affect the brain’s hypothalamus, which helps regulate temperature through sweating and shivering. Some antipsychotic medications can raise body temperature, which can have deadly effects when coupled with extreme heat. The disease affects people’s ability to make reasoned decisions or sense when they are ill. People with schizophrenia tend to have other conditions tied to heat-related illness, such as diabetes. Finally, schizophrenia is associated with isolation and homelessness, which puts people at risk when temperatures rise.

In Phoenix, the first U.S. city to create an office for addressing heat risks, “the word schizophrenia does not appear in the … heat response plan. And maybe it should,” says David Hondula, who leads the city’s Office of Heat Response and Mitigation. He notes that local data show people without housing—some of whom have schizophrenia—are two to three times more likely to die from heat than the overall population.

The findings in Canada have already prompted more research. Liv Yoon, a sociologist at the University of British Columbia, Vancouver, is preparing to delve into the stories of people with schizophrenia who survived the heat wave. “We realize there’s more going on than simply the physiological mechanism,” Yoon says. She hopes talking with survivors will shed light on social factors contributing to the surge in deaths.

As scientists warn that climate change will bring more deadly heat waves, the nonprofit British Columbia Schizophrenia Society has ramped up efforts to educate caregivers about the danger, says CEO Faydra Aldridge. “I don’t think any of us were as prepared in any area for this heat wave that happened,” she says. “Now, we’re much more aware of the potential risks for people living with schizophrenia.”

Henderson, meanwhile, chairs a provincial committee formed after the 2021 heat wave to prepare for future events. Public announcements should make much more explicit warnings, she says. “When we’re talking about risk factors for extreme hot weather, schizophrenia needs to be near the top of the list.”