Does a simulated heat event impact endothelial function in older adults?

Aging is associated with a decline in vascular function, namely a deterioration of endothelial function. This vascular rarefaction can be exacerbated during extreme heat events, which are increasing due to climate change. Thus, we aimed to compare the effect of prolonged heat exposure on endothelial function in young versus older adults. We hypothesized that endothelial function in older adults (60-80 years) would be attenuated compared to young adults (18-35 years) during and 24 hours (h) after a six-hour simulated heat event. Thirteen young (n=13; 7 F, 6 M; age 23 ± 3 years) and fourteen older (n=14; 8 F, 6 M; age 68 ± 4 years) adults participated in a six-hour simulated heat event (42ºC, 20% relative humidity). During the heat event, participants cycled at 3 METS for 15 minutes every hour to simulate activities of daily living. Flow-mediated dilation (FMD) measurements were measured 24 h before (pre-) and 24 h after (post-) the heat event. Venous blood samples were taken prior to, immediately after, and 24 h after the heat event to measure serum von Willebrand factor (vWF). FMD was greater pre- and post- heat event in young adults compared to older adults p ≤ 0.01 for interaction; young, pre: 8.1% (6.3,9.9); post: 7.6% (5.5,9.7); older, pre: 4.4% (2.9,5.8); post: 3.1% (2.0,4.2). There were no differences in FMD pre- to post-heat event in young adults (p = 0.46), but there was a trending reduction in older adults (p = 0.06). At all blood sampling time points (prior, immediately after, 24 h post-heat event), serum vWF was higher in older adults than in young adults. Furthermore, vWF was increased in older adults immediately after the heat event compared to measurements taken prior to the heat event ∆mean: -16.96 ug/mL (-32.09, -0.99), p = 0.04. Thus, the heat-induced increase in vWF and trending decrease in FMD raise concerns about potential endothelial injury in response to heat events in older adults. Supported by the Eugene and Clarissa Evonuk Memorial Graduate Fellowship. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.