As temperatures continue to rise, cognitive decline is emerging as a largely overlooked illness associated with extreme heat.
In July 2023, Phoenix and several other cities faced one of the hottest months ever documented. And while many of us grumble about the discomfort, a recent study shows that these intense heatwaves may have far-reaching consequences, especially for certain parts of the population.
“Our research finds that cumulative exposure to extreme heat can undermine cognitive health, but it does so unequally across the population,” said Eun Young Choi, a postdoctoral associate at the NYU School of Global Public Health.
Extreme heat is already known as the top culprit in weather-related deaths in the United States – claiming more lives annually than the combined might of hurricanes, tornadoes, and lightning strikes.
However, the cognitive toll of extreme heat has only recently become an area of concern. Previous research has suggested that high temperatures might negatively affect cognitive function.
Still, most of these studies have generally examined cognitive impacts shortly after brief heat exposures, leaving the long-term effects relatively uncharted territory.
Virginia Chang, the study’s senior author, elaborates on the dangers of recurring or extended heat exposures.
“Cognitive decline may not manifest right after a single heat event, but repeated or prolonged exposures to extreme heat may be detrimental,” said Chang.
“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.”
“The projected increase in extreme heat days is a growing public health concern. While exposure to extreme heat has been shown to negatively affect mortality and physical health, very little is known about its long-term consequences for late-life cognitive function,” wrote the study authors.
“We examined whether extreme heat exposure is associated with cognitive decline among older adults and whether this association differs by race/ethnicity and neighbourhood socioeconomic status.”
The researchers analyzed data from the Health and Retirement Study, conducted by the University of Michigan, which spanned 12 years (2006-2018) and included roughly 9,500 U.S. adults aged 52 and older. The comprehensive study measured participants’ cognitive function over time.
The research group also incorporated socioeconomic data about the participants’ neighborhoods. They measured each participant’s cumulative exposure to extreme heat over the study’s 12-year duration using historical temperature records from the CDC’s National Environmental Public Health Tracking Network.
The results were telling. High exposure to extreme heat was linked with faster cognitive decline in residents of impoverished neighborhoods. By contrast, those from affluent neighborhoods appeared to be shielded.
“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,” explained Haena Lee, co-first author of the study.
Interestingly, the racial disparities were pronounced as well. Black older adults exhibited faster cognitive decline due to heat exposure, a trend not observed in white or Hispanic older adults.
“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 Chang.
In light of these alarming findings, the research team advocates for local governments and health officials to develop strategic policies. Their recommendations aim to identify, support, and strengthen communication with these heat-vulnerable residents.
“When faced with high temperatures, our study reveals that vulnerable populations are experiencing compounding disadvantages,” said Choi. “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 research is published in the Journal of Epidemiology & Community Health.
Extreme heat, often characterized by temperatures that are much hotter and/or humid than average, can have a profound effect on human health. The increasing frequency and intensity of heatwaves due to climate change have made understanding these impacts even more crucial.
Symptoms can include heavy sweating, weakness, dizziness, nausea, headache, and muscle cramps. It’s essentially a sign that the body is struggling to regulate its temperature.
This is a severe and life-threatening condition that occurs when the body can’t cool down. Symptoms include a high body temperature (104°F or higher), altered mental state, nausea, and racing heart rate. If not treated promptly, it can lead to organ damage or death.
High temperatures can strain the heart, especially in individuals with pre-existing heart conditions.
Hot weather can exacerbate conditions like asthma and chronic obstructive pulmonary disease (COPD). It can also increase the concentrations of ground-level ozone, a harmful air pollutant, aggravating these conditions further.
Dehydration in high temperatures can lead to kidney stones and other renal problems.
As detailed in the NYU study, prolonged exposure to extreme heat can contribute to cognitive decline, especially in vulnerable populations.
Extreme heat can exacerbate symptoms in individuals with mental health disorders. For example, some antipsychotic, antidepressant, and antihistamine medications can affect the body’s ability to regulate temperature, making individuals more susceptible to heat-related illnesses.