Heat Tolerance in Older Adults: A Systematic Review of Thermoregulation, Vulnerability, Environmental Change, and Health Outcomes

Background: Exposure to heat is a growing health concern in the context of climate change. Older adults (people aged 600 years or older) are particularly vulnerable due to age-related physiological changes that compromise thermoregulation. Objective: To systematically review the evidence on thermoregulatory alterations in older adults exposed to heat and their association with adverse clinical outcomes. Methods: Following PRISMA guidelines, a systematic search was conducted in PubMed, Web of Science, ScienceDirect, and Scopus. Twenty-four original studies met the inclusion criteria, including experimental studies in controlled environments and epidemiological studies on heat-related outcomes. Data on study characteristics, thermophysiological responses, clinical outcomes, and methodological quality (assessed with JBI tools) were extracted and synthesized. Results: Experimental studies showed that older adults exhibit reduced sweating and cutaneous vasodilation, attenuated cardiovascular and autonomic adjustments, impaired hydration status, and altered thermal perception. These limitations resulted in greater heat storage, faster increases in core temperature, and a higher risk of dehydration and fatigue compared with younger adults. Epidemiological evidence confirmed a significant association between high ambient temperatures and increased hospitalizations and mortality among older populations, particularly at advanced ages, in women, and in those with comorbidities or socioeconomic vulnerability. Conclusions: Heat exposure and climatic conditions—particularly high ambient temperatures, humidity, and poor air quality—reduce thermoregulatory efficiency and increase risks of dehydration, cardiovascular strain, and mortality in older adults. Integrated public health actions addressing both environmental and physiological factors are essential for preventing heat-related illness among older adults.