Extreme heat may speed up cognitive decline for people from poorer neighbourhoods

Extreme heat may pose a threat to our brains, according to a new study from New York University.

According to scientists at Nasa’s Goddard Institute for Space Studies (GISS), July 2023 was hotter than any other month in the global temperature record.

With harsher summers and global temperatures on the rise, it can be quite hard for the body to adjust. As heatwaves have become more frequent due to climate change, researchers wanted to understand the connection between extreme heat exposure and cognitive decline.

“Cognitive decline may not manifest right after a single heat event, but repeated or prolonged exposures to extreme heat may be detrimental,” explained Virginia Chang, associate professor of social and behavioural 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, Professor Chang added.

The team of researchers at NYU reported that such extreme heat can worsen cognitive decline among vulnerable groups. More specifically, Black older adults and people living in poorer neighbourhoods are at higher risk – and here’s why.

Researchers analysed data from over 9,000 US adults over the age of 52, who were surveyed over a 12-year period between 2006 and 2018.

The researchers also looked at socioeconomic measures of the neighbourhoods where participants lived and calculated participants’ cumulative exposure to extreme heat (the number of days in which the heat index reached or exceeded a location-specific threshold).

As a result, researchers found that high exposure to extreme heat was associated with faster cognitive decline among residents of poor neighbourhoods, but not for those in wealthier neighbourhoods.

“Affluent neighbourhoods tend to have resources that can help in a heatwave—things like well-maintained green spaces, air conditioning, and cooling centres. In disadvantaged neighbourhoods, these resources may not exist,” said Haena Lee, assistant professor of sociology at Sungkyunkwan University, South Korea and the study’s co-first author.

“Other factors associated with disadvantaged neighbourhoods—residents experiencing chronic stress, greater social isolation, and fewer specialized services for cognitive health – could also be contributing to this disparity.

The study also looked at how extreme heat and its link to racial inequality.

Moreover, cumulative exposure to extreme heat was associated with faster cognitive decline among Black older adults, which may be due to structural racism – but not among white or Hispanic older adults.

The university release has said the study however 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,” said Professor Chang.

In the US, extreme heat has been the leading factor of weather-related deaths in the country, “claiming more lives each year than hurricanes, tornadoes, and lightning combined,” according to the NYU University release.

Children and older adults are particularly more at risk from illnesses related to heat – such as heat exhaustion and heat stroke.

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