As climate change intensifies heat events globally, the vulnerability of aging populations to heat-related illness is a growing public health concern. A key question has been whether the nervous system's declining command over cooling responses — sweating and skin blood flow — is fixed in older age, or whether it can be rehabilitated through deliberate heat exposure. The answer has significant implications for how we protect and prepare older adults for rising temperatures.
In a controlled study of 31 adults — 15 older (ages 60–78) and 16 younger (ages 21–40) — researchers measured skin sympathetic nerve activity (SSNA), local sweat rate, and cutaneous vascular conductance before and after seven consecutive days of passive hot water immersion. Critically, before acclimation, the temperature threshold at which the nervous system triggered sweating and skin vasodilation did not significantly differ between age groups, challenging the assumption that neural thermoregulatory deficits are a primary driver of heat vulnerability in older adults. After acclimation, older adults showed significant reductions in the onset threshold for all three neural markers — meaning their cooling responses engaged earlier at a lower core temperature — and these improvements were statistically indistinguishable from gains observed in younger participants.
This finding is both clarifying and somewhat surprising. The dominant narrative in thermoregulation research has framed older adults as having fundamentally compromised sympathetic control of body temperature. This study suggests the neural architecture remains plastic well into the seventh decade. The mechanism likely involves heat-induced downward resetting of the hypothalamic temperature set point and enhanced afferent sensitivity, though the study cannot fully disentangle central from peripheral adaptations. The cohort is modest in size, and participants were healthy older adults — generalizability to those with cardiovascular disease or taking vasoactive medications remains an open question. Still, the finding that passive, non-exercise-based heat exposure — achievable via hot baths — produces comparable neural thermoregulatory adaptation across age groups positions this as a practically accessible and potentially important intervention for aging populations.
