Regularly sweltering through hot outdoor temperatures could age you faster than if you lived in a cooler location.
That’s according to a new study in Science Advances, which suggests an adult living in a US state like Arizona could be biologically 14 months older than someone living in Washington State.
Study co-author and gerontologist Eun Young Choi, from the University of Southern California, said the impact of living in prolonged heat did not discriminate across different demographics.
“Even after looking at other factors — age, sex, ethnicity, education — this magnitude we found is comparable to the effects of smoking,” Dr Choi said.
Heatwaves and prolonged exposure to hot weather can have physiological effects on the human body from heart disease to kidney dysfunction.
Dr Choi said the new research set out to examine the physical toll of heat before diseases or organ dysfunction appeared.
“The effects of this extreme heat might not show up right away as diagnosable health conditions,” she said.
“But they could be taking a silent toll at the cellular or molecular level.
“So, over time, this biological deterioration could accumulate and eventually, years later, lead to disability and disease.”
To figure out if there were heat-related changes at a molecular or cellular level, Dr Choi and fellow gerontologist Jennifer Ailshire analysed blood samples from 3,686 adults over the age of 56.
Using an “epigenetic clock” technique, the researchers examined natural chemical changes to participants’ genetic code to estimate their biological age.
(Biological age can be higher or lower than chronological age, which is based on when a person is born.)
Participants’ biological ages were then compared to their location’s heat index, which was calculated from daily average temperature and humidity.
Dr Choi said people living at least a year in states with more days of extreme heat, defined in the study as 32 to 39.4 degrees Celsius, had, on average, a higher biological age than participants living in cooler states.
| Warning level | Heat index daily maximum |
|---|---|
| Caution | 26.7C to 32.2C |
| Extreme | 32.2C to 39.4C |
| Danger | 39.4C to 51.1C |
The warmest US states can experience up to 190 days of extreme heat annually.
Dr Choi said exposure to extreme heat over a shorter period appeared to have a temporary impact on a person’s biological age.
But the study did not go as far to link the heat data to mortality rates.
“Whether epigenetic age can explain this link between heat and mortality, that’s definitely the next question,” Dr Choi said.
What about in Australia?
The days can get pretty hot across Australia. Recent research indicated temperatures in places such as Sydney may be hotter than previously reported.
So could the study findings be relevant to people living in hot parts of Australia?
Dr Choi said she thought the study’s findings were relevant to other countries.
“The real-world consequences of [heat] exposure can vary significantly depending on local infrastructure, climate conditions and other available resources,” she said.
“That’s why we need really need heat adaptation strategies and not rely solely on individual methods [like air conditioning].”
Dr Choi said while extreme heat could affect anyone, its effects were not equal across a population.
“[Extreme heat] will disproportionately affect really vulnerable people, like those in prison and those who don’t have socio-economic resources to avoid outdoor heat.”
University of Sydney thermoregulatory physiologist Ollie Jay, who was not involved in the study, said it was interesting research, but he thought the heat index as a measurement was not relevant to all situations.
“They used the heat index, which incorporates humidity, but this is only useful in hot-humid climates where the environment is restricting sweat evaporation,” he said.
“In very hot and dry climates, sweat freely evaporates, but there still can be significant thermal strain because heat loss is limited by the ability to produce sweat.”
Professor Jay said there were better models to measure a person’s heat strain than a heat index.
“[They] incorporate not just the climate but activity, clothing and physiological restrictions to thermoregulation,” he said.
Professor Jay said he would like to see an assessment that incorporated other thermoregulation factors.
This way researchers could see whether individuals in the study with an older biological age had experienced the greatest physical heat stress.
Study limitations
Christian Nefzger, an epigenetics expert from the University of Queensland not involved in the research, said the study should not be over interpreted as definitive evidence of increased biological age.
“These changes may represent stress or environmental adaptations that could be reversible,” Dr Nefzger said.
“People living in extreme climates may be less likely to exercise than people living in more moderate climates, which could contribute to the study’s findings.
“More research is needed before drawing firm conclusions about the long-term consequences on true biological ageing in response to higher temperatures.”
Dr Choi acknowledged a closer look at data at the individual level was needed.
“On average people in hotter regions tend to show signs of faster ageing,” she said.
“But there are many factors at play and some individuals might be more resilient or have ways to reduce their heating.”
This is not a study that can be taken at face value and applied to Australia. Also as it says, there has been no reference back to mortality rates in the different climate zones of Australia. Indeed there is the reference to what we can call “Urban Heat Islands” that exist in densely built up areas of some of our cities.
With the very widespread adoption of airconditioning in most dwelling and work and shopping places, the majority of the Australian population will not be unduly stressed. However, our easy lifestyle with mush time spent outdoors opens up another risk factor that is very different to the Northern Hemisphere populace (especially for those in such dirty air areas as China, India, Japan, North America and much of Europe.
Those working outdoors are always advised to keep hydration and appropriate cooling systems available to avoid over heating.
Our skies are, comparatively speaking, crystal clear meaning that our exposure to all levels of Ultra Violet are much greater. Not only does this degrade all of our paints, fabrics and outdoor plastics, but our skin.
This can lead to premature ageing. Paradoxically, it is very important for good health to ensure that we have regular exposure to as much of our body as practical to sunlight so that our natural production of vitamin D can occur to keep up our natural immunities to such assaults as stray viruses.