What if extreme heat not only leaves you feeling exhausted but actually makes you age faster?

Scientists already know that extreme heat increases the risk of heat stroke, cardiovascular disease, kidney dysfunction and even death. I see these effects often in my work as a researcher studying how environmental stressors influence the aging process. But until now, little research has explored how heat affects biological aging: the gradual deterioration of cells and tissues that increases the risk of age-related diseases.

New research my team and I published in the journal Science Advances suggests that long-term exposure to extreme heat may speed up biological aging at the molecular level, raising concerns about the long-term health risks posed by a warming climate.

Extreme heat’s hidden toll on the body

My colleagues and I examined blood samples from over 3,600 older adults across the United States. We measured their biological age using epigenetic clocks, which capture DNA modification patterns – methylation – that change with age.

DNA methylation refers to chemical modifications to DNA that act like switches to turn genes on and off. Environmental factors can influence these switches and change how genes function, affecting aging and disease risk over time. Measuring these changes through epigenetic clocks can strongly predict age-related disease risk and lifespan.

Research in animal models has shown that extreme heat can trigger what’s known as a maladaptive epigenetic memory, or lasting changes in DNA methylation patterns. Studies indicate that a single episode of extreme heat stress can cause long-term shifts in DNA methylation across different tissue types in mice. To test the effects of heat stress on people, we linked epigenetic clock data to climate records to assess whether people living in hotter environments exhibited faster biological aging.

We found that older adults residing in areas with frequent very hot days showed significantly faster epigenetic aging compared with those living in cooler regions. For example, participants living in locations with at least 140 extreme heat days per year – classified as days when the heat index exceeded 90 degrees Fahrenheit (32.33 degrees Celcius) – experienced up to 14 months of additional biological aging compared with those in areas with fewer than 10 such days annually.

This link between biological age and extreme heat remained even after accounting for a wide range of individual and community factors such as physical activity levels and socioeconomic status. This means that even among people with similar lifestyles, those living in hotter environments may still be aging faster at the biological level.

Even more surprising was the magnitude of the effect – extreme heat has a comparable impact on speeding up aging as smoking and heavy alcohol consumption. This suggests that heat exposure may be silently accelerating aging, at a level on par with other major known environmental and lifestyle stressors.

Long-term public health consequences

While our study sheds light on the connection between heat and biological aging, many unanswered questions remain. It’s important to clarify that our findings don’t mean every additional year in extreme heat translates directly to 14 extra months of biological aging. Instead, our research reflects population-level differences between groups based on their local heat exposure. In other words, we took a snapshot of whole populations at a moment in time; it wasn’t designed to look at effects on individual people.

Our study also doesn’t fully capture all the ways people might protect themselves from extreme heat. Factors such as access to air conditioning, time spent outdoors and occupational exposure all play a role in shaping personal heat exposure and its effects. Some individuals may be more resilient, while others may face greater risks due to preexisting health conditions or socioeconomic barriers. This is an area where more research is needed.

What is clear, however, is that extreme heat is more than just an immediate health hazard – it may be silently accelerating the aging process, with long-term consequences for public health.

Older adults are especially vulnerable because aging reduces the body’s ability to regulate temperature effectively. Many older individuals also take medications such as beta-blockers and diuretics that can impair their heat tolerance, making it even harder for their bodies to cope with high temperatures. So even moderately hot days, such as those reaching 80 degrees Fahrenheit (26.67 degrees Celcius), can pose health risks for older adults.

As the U.S. population rapidly ages and climate change intensifies heat waves worldwide, I believe simply telling people to move to cooler regions isn’t realistic. Developing age-appropriate solutions that allow older adults to safely remain in their communities and protect the most vulnerable populations could help address the hidden yet significant effects of extreme heat.

Eunyoung Choi, Postdoctoral Associate in Gerontology, University of Southern California

This article is republished from The Conversation under a Creative Commons license. Read the original article.

If the joy of seeing butterflies seems increasingly rare these days, it isn’t your imagination.

From 2000 to 2020, the number of butterflies fell by 22% across the continental United States. That’s 1 in 5 butterflies lost. The findings are from an analysis just published in the journal Science by the U.S. Geological Survey’s Powell Center Status of Butterflies of the United States Working Group, which I am involved in.

We found declines in just about every region of the continental U.S. and across almost all butterfly species.

Overall, nearly one-third of the 342 butterfly species we were able to study declined by more than half. Twenty-two species fell by more than 90%. Only nine actually increased in numbers.

Some species’ numbers are dropping faster than others. The West Coast lady, a fairly widespread species across the western U.S., dropped by 80% in 20 years. Given everything we know about its biology, it should be doing fine – it has a wide range and feeds on a variety of plants. Yet, its numbers are absolutely tanking across its range.

Why care about butterflies?

Butterflies are beautiful. They inspire people, from art to literature and poetry. They deserve to exist simply for the sake of existing. They are also important for ecosystem function.

Butterflies are pollinators, picking up pollen on their legs and bodies as they feed on nectar from one flower and carrying it to the next. In their caterpillar stage, they also play an important role as herbivores, keeping plant growth in check.

Butterflies can also serve as an indicator species that can warn of threats and trends in other insects. Because humans are fond of butterflies, it’s easy to get volunteers to participate in surveys to count them.

The annual North American Butterfly Association Fourth of July Count is an example and one we used in the analysis. The same kind of nationwide monitoring by amateur naturalists doesn’t exist for less charismatic insects such as walking sticks.

What’s causing butterflies to decline?

Butterfly populations can decline for a number of reasons. Habitat loss, insecticides, rising temperatures and drying landscapes can all harm these fragile insects.

A study published in 2024 found that a change in insecticide use was a major factor in driving butterfly declines in the Midwest over 17 years. The authors, many of whom were also part of the current study, noted that the drop coincided with a shift to using seeds with prophylactic insecticides, rather than only spraying crops after an infestation.

The Southwest saw the greatest drops in butterfly abundance of any region. As that region heats up and dries out, the changing climate may be driving some of the butterfly decline there. Butterflies have a high surface-to-volume ratio – they don’t hold much moisture – so they can easily become desiccated in dry conditions. Drought can also harm the plants that butterflies rely on.

Only the Pacific Northwest didn’t lose butterfly population on average. This trend was largely driven by an irruptive species, meaning one with extremely high abundance in some years – the California tortoiseshell. When this species was excluded from the analyses, trends in the Pacific Northwest were similar to other regions.

When we looked at each species by its historical range, we found something else interesting.

Many species suffered their highest losses at the southern ends of their ranges, while the northern losses generally weren’t as severe. While we could not link drivers to trends directly, the reason for this pattern might involve climate change, or greater exposure to agriculture with insecticides in southern areas, or it may be a combination of many stressors.

There is hope for populations to recover

Some butterfly species can have multiple generations per year, and depending on the environmental conditions, the number of generations can vary between years.

This gives me a bit of hope when it comes to butterfly conservation. Because they have such short generation times, even small conservation steps can make a big difference and we can see populations bounce back.

The Karner blue is an example. It’s a small, endangered butterfly that depends on oak savannas and pine barren ecosystems. These habitats are uncommon and require management, especially prescribed burning, to maintain. With restoration efforts, one Karner blue population in the Albany Pine Bush Preserve in New York rebounded from a few hundred individuals in the early 1990s to thousands of butterflies.

Similar management and restoration efforts could help other rare and declining butterflies to recover.

What you can do to help butterflies recover

The magnitude and rate of biodiversity loss in the world right now can make one feel helpless. But while national and international efforts are needed to address the crisis, you can also take small actions that can have quick benefits, starting in your own backyard.

Butterflies love wildflowers, and planting native wildflowers can benefit many butterfly species. The Xerces Society for Invertebrate Conservation has guides recommending which native species are best to plant in which parts of the country. Letting grass grow can help, even if it’s just a strip of grass and wildflowers a couple of feet wide at the back of the yard.

Supporting policies that benefit conservation can also help. In some states, insects aren’t considered wildlife, so state wildlife agencies have their hands tied when it comes to working on butterfly conservation. But those laws could be changed.

The federal Endangered Species Act can also help. The law mandates that the government maintain habitat for listed species. The U.S. Fish and Wildlife Service in December 2024 recommended listing the monarch butterfly as a threatened species. With the new study, we now have population trends for more than half of all U.S. butterfly species, including many that likely should be considered for listing.

With so many species needing help, it can be difficult to know where to start. But the new data can help concentrate conservation efforts on those species at the highest risk.

I believe this study should be a wake-up call about the need to better protect butterflies and other insects – “the little things that run the world.”

Eliza Grames, Assistant Professor of Biological Sciences, Binghamton University, State University of New York

This article is republished from The Conversation under a Creative Commons license. Read the original article.