Cutaneous microvascular function is reduced in winter compared with summer in healthy young adults

Seasonal differences in temperature and ultraviolet radiation (UVR) exposure may alter NO‐mediated vasodilation in the cutaneous microvasculature. We assessed seasonal variation in cutaneous microvascular function in 10 healthy (23 ± 2; 6 men, 4 women) adults in the summer/early‐fall and winter/early‐spring. Microvascular (intradermal microdialysis and local skin heating [42°C]) endothelial function was assessed at two visits separated by ~6 months. Mean daytime (sunrise to sunset) outdoor temperature and 2‐h 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. Multivariate regression analysis evaluated the factors (temperature, UV Index, and [25(OH)D]) that best explained variance in microvascular endothelial function. The local heating response (74.37 ± 12.21 %CVC max vs. 55.89 ± 15.50 %CVC max , p = 0.009) and the NO contribution to that response (61.73% ± 9.67% vs. 38.13% ± 13.26%, p = 0.004) were lower in winter/early‐spring compared to summer/early‐fall. The best‐fit regression model suggested that 30‐day average outdoor temperature and 2‐h peak UV Index were positively and negatively associated with NO‐dependent cutaneous vasodilation, respectively. Healthy adults exhibit lower NO‐mediated cutaneous vasodilation in the winter/early‐spring compared with summer/early‐fall, which is partially explained by seasonal differences in outdoor temperature.