Summer brain drain? Extreme heat may speed up cognitive decline for certain people

NEW YORK — In what feels like is becoming an annual tradition, the entire world is ablaze again in a scorching hot summer. July 2023 was the hottest month recorded by scientists, with Western U.S. cities like Phoenix experiencing record-breaking heatwaves. The heat certainly isn’t exclusive to the United States, as people all over the world have found themselves enduring much harsher summers in recent years. While studies continue to show extreme heat is bad for the body, researchers from New York University suggest rising global temperatures may also pose a threat to our brains.

The NYU team reports that extreme heat can worsen cognitive decline among vulnerable groups. More specifically, Black older adults and people living in poorer neighborhoods are at higher risk.

“Our research finds that cumulative exposure to extreme heat can undermine cognitive health, but it does so unequally across the population,” says Eunyoung Choi, a postdoctoral associate at the NYU School of Global Public Health and the first author of the study, in a university release.

Study authors note that extreme heat is the leading cause of weather-related deaths in America. Many may be surprised to learn that heat also claims more lives each year than hurricanes, tornadoes, and lightning combined. Young children and older adults are especially vulnerable to heat-related illnesses like heat exhaustion and heat stroke.

Recent research indicates high temperatures may also interfere with cognitive function. However, those earlier projects tended to focus on a snapshot of someone’s cognition at a single time point after a brief exposure to heat. Far less is known about the long-term impact of heat on cognitive health.

Cognitive decline may not manifest right after a single heat event, but repeated or prolonged exposures to extreme heat may be detrimental,” explains Virginia Chang, associate professor of social and behavioral sciences at the NYU School of Global Public Health and the study’s senior author. “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.”

Brain activity
(© sdecoret – stock.adobe.com)

As heat waves become more and more frequent and intense due to climate change and urban heat islands, the research team sought to better understand the connection between extreme heat exposure and cognitive decline. So, they analyzed data from close to 9,500 U.S. adults (ages 52 and older) who had been surveyed over a 12-year period (2006-2018) for the Health and Retirement Study put together by the University of Michigan Institute for Social Research. That project measured participants’ cognitive function over time.

The study authors were also sure to analyze the socioeconomic measures of the neighborhoods where participants lived. Moreover, they calculated each person’s cumulative exposure to extreme heat (the number of days in which the heat index reached or exceeded a location-specific threshold) during this 12-year period using historical temperature data taken from the CDC’s National Environmental Public Health Tracking Network.

Notably, researchers also found that high exposure to extreme heat was associated with faster cognitive decline among residents of poor neighborhoods – yet not among others living in wealthier neighborhoods.

“Affluent neighborhoods tend to have resources that can help in a heat wave—things like well-maintained green spaces, air conditioning, and cooling centers. In disadvantaged neighborhoods, these resources may not exist,” adds Haena Lee, assistant professor of sociology at Sungkyunkwan University in South Korea and the study’s co-first author. “Other factors associated with disadvantaged neighborhoods—residents experiencing chronic stress, greater social isolation, and fewer specialized services for cognitive health—could also be contributing to this disparity.”

Senior man suffering from heat stroke
Senior man suffering from heat stroke (© New Africa – stock.adobe.com)

Additionally, cumulative exposure to extreme heat was found to be linked to faster cognitive decline among Black older adults, but not white or Hispanic older adults. Importantly, however, this project did not have enough participants of other races and ethnicities to include them in the analysis.

“One possible explanation for this pattern of findings is that Black older adults may have disproportionately experienced systemic disadvantages throughout their lives due to structural racism, segregation, and other discriminatory policies, all of which may affect cognitive reserve,” Prof. Chang continues.

In conclusion, study authors urge that local governments and health officials alike work toward developing policies and tools that identify residents who are susceptible to extreme heat, empower at-risk communities, map their specific needs, and ultimately develop targeted support and increased communication with identified at-risk populations.

“When faced with high temperatures, our study reveals that vulnerable populations are experiencing compounding disadvantages,” Prof. Choi concludes. “Extreme heat is a serious public health threat, and in the context of climate change, we need to focus on supporting at-risk groups in order to build resilient communities.”

The study is published in the Journal of Epidemiology & Community Health.

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