People aged 60 and over can suffer dangerous heat stress at far lower temperatures than scientists previously assumed, according to a new study published in The Lancet Public Health. Led by health researchers at Stanford University in California, the research found that older adults could face harmful, potentially fatal heat stress once global warming reaches just 1.5C above preindustrial levels, compared with a threshold of roughly 4C for younger adults. The findings suggest that as the planet continues to heat up, older people will bear a disproportionate share of the health burden from increasingly frequent and prolonged heatwaves.
The study focuses on a condition known as uncompensable heat stress (UHS), in which the body loses its ability to regulate its own temperature, raising the risk of serious illness or death. Researchers say growing numbers of people of all ages will be exposed to UHS as global temperatures rise, but older adults will experience it far more often and across much larger areas.
What did the researchers find?
The study concludes that earlier models underestimated the danger to older people because they applied a single heat-tolerance threshold, accurate mainly for younger adults, across all age groups. By separating results into three brackets — younger adults aged 15 to 39, middle-aged adults aged 40 to 59, and older adults aged 60 and above — the researchers found that intolerable heat will affect far larger populations and last far longer than previous estimates suggested.
“Our results suggest accounting for age stratified vulnerability, intolerable heat will be experienced at much larger scales and for longer durations, affecting far more people than previously thought.”
“UHS will become increasingly prevalent with global warming across all age groups. Older adults are projected to face far more frequent and widespread UHS than young adults.”
The study estimates that each additional degree of global warming exposes roughly one million more people to at least 180 hours of uncompensable heat stress annually, with older adults absorbing a disproportionate share of that burden. The researchers warn that if warming continues unchecked, parts of the tropics and subtropics could become effectively uninhabitable for older residents.
Why are older adults more vulnerable to extreme heat?
Ageing bodies are physiologically less equipped to cope with high temperatures. Older adults sweat less efficiently, their hearts must work harder to compensate for heat stress, and their blood vessels are less able to widen to help dissipate heat, all of which limit their capacity to stay cool during extreme conditions.
This vulnerability is compounded by demographic trends: the global population aged 60 and over is projected to roughly double to 2.1 billion by 2050, meaning far more people will fall into the highest-risk category just as heatwaves become more frequent and intense, particularly in low- and middle-income countries such as India and Pakistan.
How does this connect to the UK's recent heatwaves?
The findings arrive as the UK Health Security Agency has warned that 2026 is on course to become the country's deadliest year on record for heat-related deaths, after England experienced five separate heatwaves. A four-day heatwave in May and an eight-day heatwave in June together were estimated to have caused 2,877 excess deaths, almost double the total recorded over the same period the previous year.
According to a more detailed regional breakdown reported by phys.org, England and Wales recorded roughly 550 heat-related deaths during the May heatwave between the 21st and 29th, and around 2,200 during the June heatwave between the 18th and 28th, with people aged over 85 accounting for approximately 60% of all excess deaths across both episodes. The UKHSA's own interim monitoring report, cited by the government's official heat mortality report, put the total estimated heat-associated deaths for those months at 2,877, within a 95% confidence interval of 2,476 to 3,278.
Separately, a news agency report noted that this year's toll is approaching the UK's previous record of 2,985 heat-associated deaths, set in 2022 when temperatures in Britain first exceeded 40C. For background on how extreme heat physically affects the body, earlier coverage explained the dilation of blood vessels and fluid loss that drive heat exhaustion and heatstroke, while a separate report examined the rare red heat warnings issued across the UK as a wider European heatwave caused multiple deaths. A summary of the continent's 2026 heatwaves, compiled by an online reference source, also recorded roughly 480 excess deaths in the Netherlands, mostly among elderly people or those with pre-existing health conditions.
What do medical and charity experts say?
Dr Simon Williams, an expert in the health impacts and inequalities associated with heat at Swansea University, described the research as highly significant.
“This is a very significant study, with findings suggesting that heatwaves and extreme heat exposure is going to be a growing threat to human health in the coming years. In particular, it shows that heatwaves have unequal health impacts, with older adults particularly vulnerable.”
Caroline Abrahams, charity director at Age UK, said the findings should end any doubt about the scale of the threat facing older people.
“These findings are alarming. This study means there's now no denying that extreme heat poses a very real health threat to our older population.”
“High temperatures can exacerbate certain medical problems that are common among older people and, more generally, ageing bodies find it harder to adapt to more extremes of heat and cold as we age.”
Dr Hilary Williams, clinical vice-president of the Royal College of Physicians, said extreme heat should be treated as a matter of patient safety.
“Extreme weather, including severe heat, is a patient safety issue.”
“We know that heatwaves bring a surge in patients. Patients often arrive with dehydration, having collapsed, or with existing conditions like heart and kidney disease made worse by the heat. Managing multiple health conditions at once is hard enough but doing it when the body's ability to regulate its own temperature is less efficient makes it harder still.”
One hospital doctor described conditions recorded on a hospital corridor during this summer's extreme heat as inadequate for care, prompting Williams to warn:
“That is not a safe environment for patients or staff.”
What new evidence has emerged since the study?
Additional research published on 5 August 2026 by Stanford Medicine found that older adults sharply curtailed how far they travelled from home once daily average temperatures reached 84F, with the area they covered shrinking by nearly two-thirds of a square mile for every additional degree above that threshold. The finding offers direct evidence that extreme heat is already changing older people's daily behaviour and mobility, independent of any diagnosed illness.
Outside the UK, health officials in Louisiana reported eight heat-related deaths in 2026, according to a local news outlet, with seven of the eight victims aged 65 or older, underscoring that the age-related risk pattern identified in the Lancet study is also visible in real-world mortality data elsewhere.
What happens next?
The UK Health Security Agency extended amber heat-health alerts across most of England in mid-August 2026, according to the agency's official update, with some regional alerts set to expire on 15 August 2026 and others on 14 August, meaning further alerts could follow if temperatures rise again. England's interim heat mortality monitoring report may also be revised later in the year if additional heat episodes occur, which would determine whether 2026 ultimately surpasses the 2022 record of 2,985 heat-associated deaths. In the United States, local health agencies have continued to issue guidance urging residents to check on vulnerable older neighbours at least twice a day during ongoing summer heat.
Key Facts
- Older adults could face harmful heat stress at 1.5C of global warming above preindustrial levels, versus about 4C for younger adults, the Lancet Public Health study found.
- England's May and June 2026 heatwaves caused an estimated 2,877 excess deaths, nearing the 2022 record of 2,985.
- People aged over 85 accounted for roughly 60% of excess deaths during England and Wales's summer 2026 heatwaves.
- A Stanford Medicine study found older adults' daily travel range shrank by nearly two-thirds of a square mile for each degree above 84F.
- The global population aged 60 and over is projected to nearly double to 2.1 billion by 2050, increasing exposure to dangerous heat.
