Prolonged exposure to extreme heat is associated with cognitive decline in older adults, especially among Black individuals and those from disadvantaged neighborhoods, according to new research published in the Journal of Epidemiology and Community Health.
Extreme heat is currently the leading cause of weather-related deaths in the United States, surpassing even hurricanes, tornadoes, and lightning combined. The vulnerability to heat-related illnesses, such as heat exhaustion and heat stroke, is heightened among young children and older adults. Recent research has suggested that high temperatures may adversely affect cognitive function, but most studies have focused on short-term cognitive changes following brief heat exposure.
“I focus on the health of older adults, specifically examining the influence of environmental factors on their well-being,” explained study author Eunyoung Choi, a postdoctoral associate at the Leonard Davis School of Gerontology at the University of Southern California. “Given the growing concerns of climate change and its manifesting trends, such as frequent and intense heatwaves, I’m driven to understand their potential adverse health effects and the possible amplification of existing health disparities in later life.”
“While many studies have spotlighted immediate consequences of heat, like heatstroke or dehydration, our research delves deeper. We aim to comprehend the long-term health implications of consistent exposure to extreme heat.”
To conduct their research, the scientists delved into data from nearly 9,500 U.S. adults aged 52 and older. This data spanned a 12-year period, from 2006 to 2018, and came from the Health and Retirement Study conducted by the University of Michigan Institute for Social Research. The researchers also considered socioeconomic factors related to the neighborhoods where the participants lived, such as income and education levels.
One of the key measures used in the study was the number of days when the heat index reached or exceeded a location-specific threshold, a method that accounts for variations in climate zones and people’s acclimatization to heat. The researchers then calculated each participant’s cumulative exposure to extreme heat during the 12-year period, focusing on the days when the heat was particularly intense.
“Cumulative exposure to extreme heat can trigger a cascade of events in the brain, including cellular damage, inflammation, and oxidative stress, all of which can exhaust one’s cognitive reserve,” explained Virginia Chang, associate professor of social and behavioral sciences at the NYU School of Global Public Health and the senior author of the study.
Choi and her colleagues found that the number of extreme heat days varies significantly across the United States. The southern region, in particular, experiences the most extreme heat days, with an average of 12.6 hot days during the May to September period, compared to 10.5, 10.8, and 9.2 days in the Northeast, Midwest, and West, respectively.
Approximately 17.3% of the study’s sample experienced high cumulative exposure to extreme heat, defined as having at least 13.1 extreme heat days per year. This exposure was more common among Black participants (almost one-third) and residents of disadvantaged neighborhoods (22.1%).
The researchers found that extreme heat exposure had varying effects on cognitive decline based on race/ethnicity and neighborhood socioeconomic status. Among Black participants, extreme heat exposure was associated with a faster decline in cognitive function as they aged. In contrast, extreme heat exposure did not have a significant impact on the cognitive decline of White participants.
For Hispanic participants, there was no significant relationship between extreme heat exposure and cognitive function. Notably, in disadvantaged neighborhoods, high exposure to extreme heat was associated with a faster cognitive decline, whereas in average and affluent neighborhoods, no such association was observed.
“The main takeaway from our study is that prolonged exposure to extreme heat is linked to cognitive decline in older adults, but only among older Black individuals and those from disadvantaged neighborhoods. It’s not a uniform effect across all groups,” Choi told PsyPost.
“This is a significant because it’s not something that would be apparent right away. It can be a slow, gradual process that might go unnoticed until substantial damage has occurred. What’s particularly concerning is the most affected groups are those who are already at high risk for dementia.”
The findings underscore the importance of developing targeted policies and tools to identify and support individuals and communities at risk of extreme heat exposure. It is crucial to address the specific needs of these populations, considering factors like access to resources, healthcare facilities, and social support.
“One standout aspect of our results was the distinct disparities observed in the relationship between heat and cognitive decline,” Choi said. “These disparities can be understood from the broader systemic perspective. It isn’t just about individual susceptibilities; societal contexts and entrenched historical inequities may contribute to these outcomes.”
“Consider, for instance, community planning decisions such as tree placements or locations of cooling centers. These decisions, seemingly inconsequential, can have a profound impact on how varied communities experience extreme heat. In disadvantaged areas, lacking vital amenities like shade or cooling facilities, residents face exacerbated effects of heat, potentially culminating in faster cognitive deterioration. Addressing these disparities means looking beyond immediate remedies and envisioning broader societal transformations that tackle the core of the issue.”
The study provides valuable insights, but it is not without limitations. It focused on outdoor temperatures and did not account for indoor conditions or access to air conditioning, which can vary among individuals. Additionally, the cognitive tests used may not capture the full range of cognitive performance, especially among diverse populations.
“While our findings are revealing, it’s essential to extend our lens to encompass a life-course perspective,” Choi told PsyPost. “This would mean broadening our scope from just older adults to include early childhood and monitoring heat exposure across an individual’s lifespan. We are keen to investigate the impact of heat exposure during pivotal phases, especially childhood, a crucial period for brain maturation. Gaining insights into the long-term repercussions of exposure during these formative stages will enrich our understanding of the associated risks, guiding more targeted and impactful interventions.”
“Our research calls for a paradigm shift in how we approach extreme heat in the context of climate change,” the researcher added. “It’s not merely about emergency response; it’s about long-term resilience, understanding the cumulative effects. We need to think about the long-term consequences of living in a world where extreme heat is becoming the norm. We need to consider how our cities are designed, how our communities are built, and how our healthcare systems are prepared to handle the chronic effects of heat exposure.”
The study, “Cumulative exposure to extreme heat and trajectories of cognitive decline among older adults in the USA“, was authored by Eun Young Choi, Haena Lee, and Virginia W. Chang.
