According to a new study by researchers from the Yale School of Public Health (YSPH) and Yale School of Medicine, short-term exposure to high ambient temperatures may significantly increase the risk of stroke among people aged 18 to 64 years, especially women.
The study, which analyzed the health records of over one million individuals nationwide, highlights a growing concern about how climate change could worsen health outcomes in understudied populations.
"Climate change is one of the most significant public health challenges of our time," said Dr. Xiaomei Ma, PhD, a professor and interim chair of the Department of Chronic Disease Epidemiology at YSPH. "It is critical to assess the health impact of different aspects of climate change so we can better adapt and potentially intervene." Ma, co-senior author of the study, noted that 2024 is on track to be the warmest year on record.
The study, published today in the Journal of the American College of Cardiology, focused on adults aged 18 to 64 years, a demographic group that has seen an increasing burden of stroke in recent years, the authors said.
As global temperatures rise, the health impacts of extreme heat have become a pressing issue. Strokes, which are typically linked to factors such as high blood pressure and sedentary lifestyles, can also be triggered by environmental factors like temperature, the authors said. Many previous studies on this connection have focused on adults aged 65 years and older, leaving a gap in understanding how heat exposure may impact younger individuals, according to the authors.
The Yale research revealed that short-term exposure to high ambient temperatures - defined as the current day to the previous six days - can be a significant stroke risk factor for younger adults, said Dr. Kai Chen, PhD, an associate professor of epidemiology (environmental health sciences) at YSPH and the study's co-senior author. Notably, Chen said, the study found women were more vulnerable to high ambient temperatures than men.
Accounting for the finding, Chen explained: "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."
The research leveraged a large, nationwide health claims database, providing broad geographic coverage across the United States. By examining over one million individuals aged 18-64 years, the researchers evaluated how short-term exposure to both high and low temperatures influenced stroke risk. The study also incorporated demographic data and used the Social Deprivation Index, a measure that quantifies the level of socioeconomic disadvantage in a given area, to account for sociodemographic factors that could contribute to stroke vulnerability.
The findings could have significant implications for public health policy, particularly as climate change continues to pose new challenges, the authors said. Not only does the study identify temperature as a modifiable environmental risk factor for stroke, it also emphasizes the need for targeted interventions that protect at-risk populations, particularly younger adults and women.
The study also adds to the growing body of evidence that rising temperatures could exacerbate health disparities, said Chen. Not only is the number of young adults who experience stroke currently growing, but many individuals in this age range could also face a disproportionate burden of climate change due to the need to work outdoors or a lack of means to cope with extreme temperatures, the authors said.
Chen and Ma said the study highlights the value of cross-disciplinary collaboration. They decided to work on the current study after a chance encounter two years ago. Their diverse academic backgrounds allowed them to approach the issue of stroke risk from both environmental health and chronic disease perspectives.
"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," Ma said. "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 authors of the study include Dr. Lingzhi Chu, PhD, and Dr. Rong Wang, PhD, from YSPH, and Dr. Cary Gross, MD, of both the Yale School of Medicine and YSPH.