Heat waves may accelerate the aging process

Every day, Kalpana Suryawanshi, 48, looks into the mirror and whispers, "I look older than my age."

Eight years ago, she was diagnosed with Type 2 diabetes. Since then, her health has deteriorated, which she attributes to increased exposure to heat while working in the fields, planting crops, harvesting produce, and carrying heavy loads of cattle fodder. During this time, she frequently experienced dizziness and weakness as temperatures exceeded 40 degrees Celsius (104 F) in her village of Nandani in Maharashtra state, India.

Heat is known to affect cognitive function, cardiovascular health, and kidney function, and a growing body of research suggests that exposure to rising temperatures also accelerates the body's aging process. A 2023 German study published in Environment International was the first to find that higher air temperatures are associated with faster aging at the cellular level. It found that prolonged exposure to elevated temperatures can make the body age faster than its chronological age, a phenomenon known as epigenetic age acceleration. Scientists measure this process using epigenetic clocks, which analyze chemical markers called DNA methylation that turn genes on and off. The study found that in areas where the average annual temperature is 1°C higher, people tend to show signs of accelerated aging at the cellular level.

2024 was the hottest year on record, with 6.8 billion people worldwide experiencing extreme heat for at least 31 days. One unusual effect of this rising heat is observed firsthand by India's community health care workers, who report that more people appear older than their actual age.

How heat could accelerate aging

Scientists are now also finding the biological mechanisms that contribute to premature aging. Wenli Ni, a postdoctoral research fellow at Harvard T.H. Chan School of Public Health and the lead author of the German study, said heat exposure can induce alterations in DNA methylation, which is a biological process that can influence gene expression and cellular function.

She explained that this mechanism can trigger harmful biological processes and accelerate aging. "Heat exposure may also lead to oxidative stress, resulting in DNA damage that could alter DNA methylation patterns and impact aging," she added. Oxidative damage occurs when unstable molecules called free radicals attack cells. They can harm DNA, cell membranes, and proteins, contributing to aging, cancer, and cardiovascular health issues.

These results were repeated in Taiwan, where scientists examined over 2,000 people and found high ambient temperature and heat index exposure were linked to increased aging, with stronger associations in prolonged exposure. The study revealed that a 1°C increase in the 180-day average temperature was linked to a rise of 0.04 to 0.08 years in biological age acceleration, as measured by three different epigenetic aging clocks that estimate biological age.

Related: Human aging accelerates dramatically at age 44 and 60

While this increase in age acceleration might seem small at first, it's important to consider how these effects can build up over time. Even slight increases in biological aging, when sustained year after year, can add up to several years of accelerated aging. This can mean an earlier occurrence of age-related illnesses. Moreover, when these small shifts affect large populations, they can contribute to a tremendous rise in disease burden and health care costs.

A recent study published in Science Advances examined the relationship between heat and aging in more than 3,500 adults aged 56 and above in the U.S. The study found that long-term heat exposure, lasting from one to six years, was associated with epigenetic aging. Persistent exposure to high temperatures can result in frequent sleep disturbances, raising stress and anxiety levels. Over time, this physiological degradation accumulates and may accelerate health decline with age.

Women disproportionately affected

The German study found that women and individuals with obesity or Type 2 diabetes exhibited stronger associations between air temperature and aging. Women generally sweat less and have different body responses to heat, which can make it harder for them to cool down and sometimes cause their body temperature to rise faster, Ni explained.

She also said that studies suggest women have a higher threshold for activating the sweating mechanism at high temperatures, indicating their bodies take longer to start sweating.

Diabetes also makes people more susceptible to high temperatures. People with diabetes often have reduced blood flow to their skin, which can interfere with the body's ability to release heat and stay cool in hot weather.

Additionally, body fat can act as insulation, making it harder for heat to move from the body's core to the skin, reducing its ability to release heat and stay cool.

Epigenetic age acceleration can contribute to cardiovascular diseases, cancer, diabetes, and mortality, putting more pressure on public health care systems.

In 2016, Rajma Jamadar, now 47 years old, from Maharashtra's Haroli village, woke up in the middle of the night with irregular heartbeats. The next day, the doctor said that her blood pressure spiked and prescribed lifelong medication. Within months, her symptoms worsened as her cardiovascular health declined. "Upon further diagnosis, the doctor then told me my heart isn't pumping blood efficiently," she said.

She prepares meals for 175 children at a public school in her village, but rising temperatures make her job increasingly difficult as the heat from cooking takes a toll on her. "Every day, I feel sick," she said.

The risks could start even before birth

Remarkably, climate change may sometimes accelerate epigenetic aging in children even before birth. A study published last year in Nature examined 104 drought-exposed children and 109 same-sex sibling controls in northern Kenya. It found a positive association between in-utero drought exposure and aging, emphasizing that the stressors from drought may decrease overall life expectancy.

According to study author Bilinda Straight, changes can happen through three key pathways in the body. The first is the immune system, the body's first line of defense that protects one from infections and diseases. The second involves metabolic processes that provide the body with energy. The third is responsible for maintaining and repairing cells in response to stress.

"Whether the threat we face is physical or emotional, we still perceive it as a danger to our homeostasis, a health-preserving balance between all our physiological systems," she explained. This suggests that the emotional stress experienced by the women in the study, along with caloric restriction and dehydration, activated systems that help the body manage stress but can harm health if overactivated for extended periods.

Women in the study were seen to be engaged in outdoor labor while they were also experiencing hunger and dehydration. "Those physiological stressors were accompanied by worry about the next meal, for themselves, their children, and loved ones," she added.

Moreover, social factors like gender inequality exposed women to coercion, overwork, and violence. While farmers risk loss from drought, those in livestock agriculture suffer the emotional and financial toll of watching their animals die. Combined with heat stress, dehydration, and hunger, this creates immense hardship. Eventually, this maternal stress during pregnancy contributes to changes in DNA methylation in their children, Straight said.

She suggests adequate nutrition and close monitoring of children's cardiovascular and metabolic health. Researchers advocate for long-term studies to better understand the impacts of the environment on epigenetic age acceleration. "Slowing down epigenetic age acceleration is going to be tied to increasing food security and identifying alternatives to women engaging in high-risk occupational labor," she added. Effective policies are needed to achieve food and livelihood security while reducing social and economic inequalities.

However, for many women, economic insecurity and the lack of social safety nets make it nearly impossible to prioritize health. Suryawanshi's struggle highlights this problem. So far, she has spent over 600,000 Indian rupees ($7,046) on medical treatment. "I can't afford any more expenses, so I've stopped taking some medicines," she said. She visited eight hospitals in two years to search for an effective treatment. "It's a miracle that I survived. Despite being only 48, I have no strength left, but I still have to work."

This article was originally published by Yale Climate Connections.