Association of sleep-wake rhythm and sleep quality with endothelial function in young adults.

Objective: The environment in modern society could disturb the sleep-wake rhythm. We aimed to study the association of sleep-wake rhythm with endothelial function and sleep quality. Material and Methods: Thirty-one healthy university students (mean age: 20.4±1.8 years) were enrolled. The endothelial function was evaluated with the percent endothelium-dependent flow-mediated dilation of the brachial artery [%FMD: (maximum diameter - baseline diameter)/baseline diameter x 100] using the high-resolution ultrasonography. We also measured the total sleep time (TST), sleep effciency, and the standard deviation (SD) of sleep timing (midpoint between bedtime and wake-up time) using the actigraphy. The irregular sleep-wake rhythm was defined as having the shift of bedtime or wake-up time for two hours or longer. Results: The %FMD and sleep efficiency were significantly lower in the irregular group than regular group (%FMD: 6.1±2.4 vs. 10.9±2.3, p<0.001, sleep effciency: 92.2±5.8 vs. 95.9±2.8%, p=0.027), whereas there was no significant difference in %FMD between the two groups of TST <6 hours and TST ≥6 hours. The %FMD was significantly correlated with SD of sleep timing (r=-0.481, p=0.006). Multiple regression analyses, including age, sex, TST, sleep effciency, and SD of sleep timing revealed that the SD of sleep timing was a significant factor associated with %FMD (ß=-0.454, p=0.017). Conclusion: Our findings suggest that the irregular sleep-wake rhythm and poor sleep quality could have adverse effects on endothelial function in young adults.