The Silent Scourge: How Extreme Heat Accelerates Aging
The relentless rise in global temperatures isn’t just about melting glaciers and rising sea levels. It’s also quietly impacting our health, accelerating the aging process at a cellular level, according to groundbreaking research. This invisible threat disproportionately affects vulnerable populations and carries significant implications for public health as the planet continues to warm.
Imagine two men, both in their 60s, with similar lifestyles and socioeconomic backgrounds. One lives in the arid climate of Arizona, the other in the temperate Pacific Northwest of Washington state. Despite their shared demographics and habits, the Arizonan is biologically older – a full 14 months older – than his Washingtonian counterpart. The reason? Prolonged exposure to extreme heat.
A recent study published in the journal Science Advances reveals a disturbing connection between chronic heat exposure and accelerated aging. Researchers found that living in areas with frequent high temperatures can age individuals at a rate comparable to habitual smoking. As global average temperatures soar due to the greenhouse gas effect, fueled by the burning of fossil fuels, a larger proportion of the global population is exposed to this silent health hazard.
The statistics paint a grim picture. Since 1999, extreme heat has claimed the lives of over 21,000 Americans. The year 2023 saw record-breaking heatwaves across the globe, with Phoenix, Arizona, enduring 31 consecutive days of temperatures exceeding 110 degrees Fahrenheit. That year shattered global temperature records, a record quickly surpassed in 2024, indicating a dangerous accelerating trend.
The health repercussions of prolonged heat exposure are multifaceted and far-reaching. In the short term, individuals can experience heat-related illnesses such as dehydration, fainting, and, in severe cases, heat stroke, a life-threatening condition. Older adults and young children are particularly susceptible due to their limited ability to regulate their body temperature effectively.
However, the long-term consequences are even more concerning. Chronic heat exposure can exacerbate existing chronic conditions like kidney and cardiovascular disease, and significantly increase the risk of mental health issues, including depression, anxiety, and even dementia. The study underscores the importance of understanding these insidious effects of heat, even in individuals who may not exhibit overt symptoms of heat-related illness.
Eun Young Choi, a postdoctoral gerontological researcher at the University of Southern California’s Leonard Davis School of Gerontology and the lead author of the study, embarked on a mission to unravel the underlying mechanisms driving the long-term health consequences of extreme heat exposure at a cellular level. Her focus was specifically on individuals nearing their 60s, seeking to understand the subtle, "nonclinical manifestations" of heat exposure. She hypothesized that chronic heat was gradually undermining overall health, regardless of whether individuals experienced acute heat-related symptoms.
To test this hypothesis, Choi meticulously analyzed blood samples from over 3,600 participants aged 56 and above who were part of a large-scale national health and retirement study. These participants had provided blood samples in 2016 or 2017. Choi, in collaboration with her coauthor, Jennifer Ailshire, then leveraged weather and climate data to estimate the number of "heat days" each participant had been exposed to in the years, months, and days leading up to their blood test. The National Weather Service defines "heat days" as days with temperatures exceeding a certain threshold.
The participants were then stratified into demographic groups based on factors such as race, socioeconomic status, exercise habits, and other relevant variables. Choi and Ailshire subsequently compared individuals within these groups using a battery of biological tests designed to assess the rate at which their cells were aging.
The results were striking. "With longer-term heat exposure – one year and six years – we see a consistent association between heat and [cellular] age across different biological tests," Choi explained. The study revealed that individuals residing in areas where temperatures remained at or above 90 degrees Fahrenheit for half the year exhibited up to 14 months more biological aging compared to their counterparts living in areas with fewer than 10 days of such extreme heat.
"This study is one of the first empirical assessments suggesting that longer-term exposure to heat is directly associated with an acceleration of the aging process," stated Vivek Shandas, a professor at Portland State University who specializes in the effects of climate change on cities. He emphasized that this research "adds to the existing work by suggesting that near-term mortality may be the result of older adults having longer-term and periodic exposures to heat."
While previous studies had hinted at a link between heat exposure and accelerated aging, and experiments in mice consistently demonstrated that heat ages cells, Choi’s study stands out as the first nationally representative research to definitively establish this connection in humans. The sheer size and diversity of her subject pool helped to minimize the influence of confounding factors, making the findings more robust. Notably, Choi did not observe any major differences in the impact of heat across various demographic groups, indicating that heat’s damaging effects on cells are pervasive in older individuals, regardless of race or socioeconomic status.
However, the study also acknowledged certain limitations. It did not fully account for the adaptive measures individuals take to protect themselves from heat. For instance, wealthier individuals may have the luxury of staying indoors in air-conditioned environments throughout the day and night, mitigating their exposure to extreme temperatures.
Prior research has consistently demonstrated that the impacts of extreme heat are not evenly distributed across populations. People living in urban areas characterized by sparse tree cover and extensive concrete surfaces, known as urban heat islands, are particularly vulnerable. These heat islands can experience temperatures up to 7 degrees Fahrenheit higher than surrounding rural areas. Moreover, urban heat islands tend to be concentrated in neighborhoods historically inhabited by marginalized communities due to discriminatory zoning practices. This is a key factor contributing to the disproportionate exposure of people of color to severe heat in urban environments compared to non-Hispanic white individuals. Furthermore, these communities are often less likely to have access to affordable air conditioning, further exacerbating their vulnerability.
"We know that some demographics, such as those working outside, unhoused populations, people living in urban heat islands, incarcerated populations, and lower-income residents generally have longer periods of exposure to extreme heat (over decades)," Shandas pointed out. "Accordingly, we might draw on these findings to suggest that some certain populations will need greater attention and care as we see forecasts for heat waves."
Choi expresses hope that future research will delve deeper into these disparities, particularly given the projected demographic shift. By 2040, it is estimated that 1 in 5 Americans will be 65 or older, a significant increase from 1 in 8 in the year 2000. The implications of Choi’s study extend beyond older adults, however. "I don’t think the underlying biology is significantly different," she said. "We would expect to see some significant effects of heat in younger adults. And we really need to track people from their birth to older ages to see whether any of these effects can be reversible."
The study serves as a stark reminder of the far-reaching consequences of climate change. It underscores the urgent need for proactive measures to mitigate greenhouse gas emissions and adapt to a warming world. This includes strategies such as expanding access to air conditioning, promoting tree planting in urban areas to combat the urban heat island effect, and developing public health interventions tailored to protect vulnerable populations from the harmful effects of extreme heat. Ignoring this silent scourge will have dire consequences for the health and well-being of current and future generations.
