Extreme Heat Risk to Elderly Far Higher Than Estimated, Stanford Finds

Why Older Adults Are More Vulnerable

As people age, the body loses its natural ability to cool itself. Older adults sweat less and their hearts must work harder because blood vessels do not expand as much. When temperatures climb, the body eventually reaches a point at which it cannot cool quickly enough to compensate, a condition known as uncompensable heat stress. This threshold is reached much sooner and at lower temperatures by elderly people than by younger adults.

Warming around the world is occurring at a speed not seen in the past 10,000 years, according to NASA data cited in the study. Simultaneously, the global population is ageing due to longer life expectancies and falling fertility rates, meaning a greater proportion of people are exposed to severe heat. Elderly people in low-income countries such as China, India and Pakistan are likely to face the highest risk even at just 1.5C of warming above preindustrial levels.

How Heat Affects the Body and Deaths

Chris Mullington, honorary clinical senior lecturer at Imperial College London in the United Kingdom, explained that earlier assessments often assumed everyone could tolerate heat as well as a healthy young adult, which substantially underestimated the risk to older people. The new study reinforces that dangerous heat cannot be defined by one universal temperature threshold because it depends partly on who is being exposed.

Mullington noted that the 180-hour exposure figure is accumulated across the year and not necessarily continuous. It describes exposure to potentially uncompensable conditions rather than meaning everyone affected will inevitably become ill. Conditions a healthy young adult might tolerate could cause an older person to store heat, experience a rising core temperature and suffer serious illness including heatstroke.

The study attributed most heatwave deaths to comorbidities, particularly cardiovascular, renal and respiratory conditions exacerbated by elevated body temperature, rather than to direct overheating alone.

Mitigation and Next Steps

The researchers concluded that understanding where, when and to what extent human heat tolerance limits will be breached is increasingly important for developing mitigation strategies. Recommended adaptations include expanding green infrastructure, enhancing ventilation, reducing heat emissions, establishing cooling centres and improving heat warning and response systems.

Since most heat-related deaths among older adults occur indoors, the study also urged broader access to air-conditioning and other cooling facilities supported by resilient energy infrastructure. In the long term, reducing emissions remains the key to controlling global warming.