Exposure to extreme heat triggers a cascade of physiological responses that can overwhelm the body’s cooling mechanisms, particularly in vulnerable populations. The US Centers for Disease Control and Prevention has documented rising heat-related illness across multiple age groups, with certain individuals—elderly people, those with chronic conditions, and outdoor workers—facing disproportionate risk during summer months.
Heat-Related Emergency Department Visits by Age Group
United States, per 100,000 population during peak summer months
Source: CDC Environmental Health Tracking Network, 2023 | Georgian Medical Journal News
Core physiological mechanisms of heat stress
When ambient temperature rises, the human body activates thermoregulation—a complex process in which blood vessels dilate near the skin surface to increase heat dissipation, and the sweat glands intensify evaporative cooling. However, this adaptive response demands substantial cardiovascular and metabolic resources, placing strain on the heart and circulatory system.
The body’s core temperature normally hovers around 37°C (98.6°F). When internal temperature exceeds 39°C, heat exhaustion can develop, marked by profuse sweating, weakness, and tachycardia. If core temperature reaches 40–41°C, heat stroke—a medical emergency—can occur, characterized by loss of thermoregulatory control and potential organ damage. Research published in The New England Journal of Medicine emphasizes that heat stroke carries mortality rates between 10% and 65%, depending on age and comorbidity profile.
Why older adults and patients with chronic disease face heightened vulnerability
Adults aged 65 and older show significantly elevated risk during heat waves, experiencing emergency department visit rates nearly 6.5 times higher than children under five, according to CDC data. This disparity reflects age-related declines in cardiovascular efficiency, reduced sensation of thirst, and impaired sweating response—all of which compromise the body’s cooling capacity.
Patients with hypertension, diabetes, cardiovascular disease, and respiratory conditions face compounded risk. Many commonly prescribed medications—including beta-blockers, diuretics, and anticholinergics—further impair heat dissipation or increase dehydration. A systematic review in The Lancet found that individuals taking three or more medications showed a 40% elevation in heat-related hospitalisation risk compared to those on no regular medication.
Environmental and occupational factors amplify exposure risk
Heat vulnerability is not uniformly distributed. Outdoor workers—including agricultural labourers, construction crews, and emergency responders—face prolonged exposure without adequate cooling breaks. Urban populations in areas with limited tree cover and dense infrastructure experience urban heat island effects, where surface temperatures can exceed ambient air temperature by 5–7°C, according to analysis from the World Health Organization.
Socioeconomic factors compound physiological risk. Individuals with limited access to air conditioning, reliable electricity, or cooling centres during heat emergencies, along with those experiencing homelessness or living in densely populated informal settlements, face substantially higher mortality. A PubMed-indexed cohort study found that social isolation—often correlated with poverty—was an independent predictor of heat-related death in adults over 75, independent of medical comorbidities.
Heat stroke—defined as core body temperature exceeding 40°C with central nervous system dysfunction—carries a mortality rate of 10–65%, with rates highest in unacclimatised older adults and those with multiple comorbidities.
— The New England Journal of Medicine, 2023
Key takeaways
- Heat-related illness kills over 1,220 Americans annually, with emergency department visits concentrated in adults aged 65 and older at 92 per 100,000 population
- Medications including beta-blockers, diuretics, and anticholinergics impair thermoregulation and increase hospitalisation risk by up to 40%
- Older adults, outdoor workers, and socioeconomically disadvantaged populations face disproportionate risk due to impaired cooling capacity and limited access to air-conditioned spaces
- Urban heat islands can elevate surface temperatures by 5–7°C above ambient air temperature, intensifying exposure in city centres
Frequently asked questions
At what core body temperature does heat stroke occur?
Heat stroke—a medical emergency requiring immediate cooling intervention—develops when core body temperature reaches 40°C (104°F) or higher and thermoregulatory mechanisms fail, according to The New England Journal of Medicine. Symptoms include cessation of sweating, confusion, seizures, and loss of consciousness. Rapid cooling to below 39°C within the first hour of treatment significantly improves survival.
Why do elderly people have reduced heat tolerance?
Age-related physiological changes include reduced cardiac output during thermoregulation, attenuated sweating response, blunted thirst sensation, and impaired peripheral vasodilatation. These adaptations collectively reduce the body’s capacity to dissipate heat, making older adults vulnerable to rapid progression from heat exhaustion to heat stroke, particularly if dehydration develops.
Can common medications increase heat-related illness risk?
Yes. Diuretics promote fluid loss; beta-blockers reduce cardiac output; and anticholinergics suppress sweating. A systematic analysis in The Lancet found that polypharmacy (three or more medications) increased hospitalisation risk by 40%. Patients on these medications should maintain hydration, avoid midday sun exposure, and monitor for heat exhaustion symptoms during warm weather.
As climate change drives more frequent and intense heat waves across temperate and tropical regions, public health responses must prioritize identifying and protecting high-risk populations through targeted cooling interventions, medication review programmes, and equitable access to air-conditioned public spaces. Occupational heat exposure standards, urban greening initiatives, and real-time heat health alert systems represent evidence-based strategies that have demonstrated effectiveness in reducing heat mortality in cities across North America and Europe. For more information on vulnerable populations, see our coverage of global health threats and patient safety interventions.
Source: What does hot weather do to the body?
