The newfound risk of heatwaves

In a world increasingly defined by searing summers and record-breaking temperatures, driven by global warming and the resulting climate change, the health risks of heatwaves have become tragically familiar.

We’ve long understood their immediate dangers: heat stroke, dehydration, and a sharp spike in hospitalizations and deaths.

Yet, new and groundbreaking research is revealing a far more insidious and lasting consequence — one that quietly erodes our health on a molecular level.

A major study published recently in the prestigious journal Nature Climate Change has presented compelling evidence that repeated exposure to heatwaves can accelerate a person’s biological aging.

While your birth date remains fixed, this research shows that your body’s internal clock can speed up, leaving you biologically older than your chronological age.

The findings represent a “paradigm shift” in how we view the public health crisis of extreme heat, suggesting that even if a heatwave doesn’t kill you, it may be silently shortening your life.

While this study zeroes in on human biology, it’s part of a broader narrative of climate-driven risks.

Other research highlights how urban heatwaves disproportionately affect older populations, particularly in cities with underdeveloped infrastructure, most notably in low- and middle-income countries such as South Africa.  

Consequently, rising heat exposure isn’t just a matter of immediate discomfort — it’s a long-term, systemic strain on vulnerable bodies, often in regions that are already socially and economically marginalised.

The study, led by researchers at the University of Hong Kong, followed over 24,000 adults in Taiwan for 15 years, meticulously analysing their medical records and linking them to a history of heatwave exposure.

The researchers did not simply rely on chronological age but instead calculated each person’s biological age using a sophisticated set of biomarkers, including measures of blood pressure, inflammation, cholesterol, and the function of vital organs like the liver and kidneys.

This biological age, which reflects the true health and function of the body’s cells and systems, was then compared to their calendar age.

The results were stark. The study found that individuals who experienced more frequent and intense heatwaves displayed a corresponding increase in their biological age.

For every significant step-up in cumulative heat exposure over a two-year period, a person’s biological age accelerated by an additional eight to 11 days.

While this may sound like a small number, scientists warn that the cumulative effect over a lifetime could be substantial.

The impact of vulnerable populations

One of the study’s most alarming findings was the disproportionate impact on certain vulnerable populations.

Manual labourers, rural residents and people living in areas with fewer air conditioning units were the most affected.

For outdoor workers, who endure the full brunt of rising temperatures, the effect was more than tripled, adding nearly a month of accelerated aging for the same increase in heat exposure.

The findings have serious implications for South Africa, where rising temperatures and frequent heatwaves are already a reality.

Older adults, some of whom work on farms and other outdoor spaces, face higher risks of heat-related accelerated ageing, potentially increasing the burden of age-related illnesses such as heart disease and diabetes.

Other vulnerable groups include people living in informal settlements without cooling infrastructure.

From stress to cellular damage: how heat accelerates aging

So, how exactly does extreme heat cause our bodies to age faster? The study authors and other researchers point to a variety of plausible cellular mechanisms.

One key suspect is DNA damage. Our cells are constantly under attack from stressors, and high temperatures can significantly increase this burden.

This thermal stress can disrupt crucial cellular processes, leading to the fragmentation of mitochondria—the “powerhouses” of our cells. When these energy factories are compromised, the entire body suffers.

Another potential culprit is telomere shortening. Telomeres are protective caps at the ends of our chromosomes, and they naturally shorten as we age.

When they become too short, cells can no longer divide and may die, leading to tissue and organ dysfunction.

Research has shown that environmental stressors, including heat, can accelerate this shortening, effectively fast-forwarding the aging process.

The study also highlights the role of epigenetics. While our DNA sequence is fixed at birth, our genes can be “turned on” or “off” by environmental factors through a process called methylation.

Heat stress can alter these methylation patterns, changing how our genes are expressed and influencing our rate of aging.

A previous study from the University of Southern California (USC) found that older adults in neighbourhoods with frequent extreme heat days aged up to 14 months faster than their counterparts in cooler regions, even after accounting for socioeconomic differences.

That research found that the effect was comparable to the health impact of long-term smoking or heavy drinking.

The need for adaptation

The findings from this new research serve as a stark warning and a call to action for governments, urban planners, and individuals. For too long, heat has been considered a temporary discomfort, not a chronic health threat.

As climate change makes heatwaves more frequent, intense, and prolonged, the long-term health consequences could be immense, particularly for rapidly aging populations in both developed and developing countries.

The research suggests that even if people are not at immediate risk of death from a heatwave, there may still be a lasting effect that increases their vulnerability to age-related diseases later in life.

This new understanding underscores the urgent need for robust heat mitigation strategies.

Policymakers and city planners should prioritise initiatives like expanding urban green spaces, planting more shade trees, and redesigning infrastructure to keep cities cooler.

For individuals, the findings emphasise the importance of seeking out cool spaces, staying hydrated, and being aware of how our bodies, and those of our family members, are reacting to heat.

In the case of South Africa where the exposure to heat conditions is already a reality faced by many.

The country must urgently invest in heat-resilient urban planning, healthcare systems prepared for chronic disease surges, and targeted support for high-risk populations, or the social and economic costs could be severe.

• Dr Enock Sithole is the executive director of the Institute for Climate Change Communication.