Microvascular, but not macrovascular, function is reduced in winter compared with summer in healthy young adults

Cardiovascular events and death rates are highest during the winter months. Endothelial dysfunction, characterized by reduced nitric oxide (NO) bioavailability, is a non-traditional risk factor for cardiovascular disease (CVD) that typically precedes the development of hypertension and increases CVD risk. Therefore, we assessed seasonal variation in endothelial function in 14 young, healthy (23 ± 2; 6 men, 8 women) adults in the summer/early-fall and winter/early-spring. Microvascular [intradermal microdialysis and local skin heating (42°C)] and macrovascular [flow-mediated dilation (FMD)] endothelial function was assessed at two visits separated by ~6 months. Mean daytime (sunrise to sunset) outdoor temperature and 2-hr peak UV Index were recorded for the 30 days prior to each experimental visit. Serum vitamin D concentrations [25(OH)D] were measured for each visit. Ordinary least squares regression analyses were used to determine the factors (temperature, UV Index, and [25(OH)D]) that best explained the variance in microvascular endothelial function. The magnitude of the local heating response (76.51 ± 13.00 %CVCmax vs. 57.60 ± 16.52 %CVCmax, P = 0.005) and the NO contribution to that response (64.13 ± 11.50% vs. 40.65 ± 15.09%, P = 0.0003) were attenuated in winter/early-spring compared to summer/early-fall. Conversely, FMD responses were not different (P ≥ 0.51) between seasons. 30-day average outdoor temperature and 2-hr peak UV Index, but not serum [25(OH)D], were included in the multivariate regression model and were positively and negatively associated with NO-dependent cutaneous vasodilation, respectively. Healthy young adults exhibit attenuated NO-mediated cutaneous vasodilation in the winter/early-spring, which may be partially explained by cooler outdoor temperatures. 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.