The findings show that a short period of exposure to high ambient temperatures—from the current day up to six days prior—can sharply increase stroke risk, particularly for women.

Dr Kai Chen, co-senior author and an associate professor of epidemiology at YSPH, explained that “the vulnerability in women is biologically plausible given the different physiological conditions and stroke risk factors in women and men, such as pregnancy or hormonal changes around menopause. But more research is needed to better understand the contribution from both biological and socioeconomic factors in the sex differences that we observed.”

Utilising a large health claims database covering over a million people across the United States, the study is among the largest to examine temperature exposure and stroke risk in younger adults. The researchers incorporated the Social Deprivation Index, which quantifies the socioeconomic disadvantages of different areas, to account for factors that may contribute to stroke vulnerability.

The findings point to significant implications for public health policy, particularly as the frequency of extreme weather increases. The study identifies temperature as a modifiable environmental risk factor for stroke, emphasising the need for preventive measures that target at-risk groups—namely younger adults and women.

Dr Chen added that the research highlights how rising temperatures could exacerbate existing health disparities. With an increasing number of younger adults experiencing strokes, those working outdoors or lacking resources to mitigate extreme heat are at heightened risk.

The study’s origins lie in a chance meeting two years ago, as Dr Ma shared. “Kai and I met for the first time two years ago, at a party in the beautiful backyard of a faculty member from the Yale School of the Environment. We chatted about what each of us was doing in our research, were inspired by each other, and concluded that it would be very nice to collaborate. Sometimes people say that and do not necessarily follow up, but both of us sprang into action.”

Other contributors to the study include Dr Lingzhi Chu and Dr Rong Wang from YSPH, and Dr Cary Gross from Yale School of Medicine. The findings mark a step forward in understanding the nuanced ways climate change may affect health, offering a foundation for further research and interventions that address these emerging risks.