Researchers of this study were particularly interested in looking at the impact of mild sleep restriction measures of oxidative stress in endothelial cells—the cells that line blood vessels. 

Why? Well, blood vessels comprise the body’s vascular system, which is responsible for delivering oxygen-rich blood to every part of the body and sweeping away waste products. While the heart provides the force needed for blood to move throughout the body, the health of individual blood vessels also significantly impacts the brain. 

Blood vessels are susceptible to damaging oxidative stress (aka an imbalance of beneficial antioxidants to harmful free radicals). This is a major risk factor for heart disease—the leading cause of death in women. 

By understanding how a common experience many women in their 30s and 40s have (periods of not sleeping enough) on a common risk factor of the number one killer of women, we can take a more targeted approach to reducing that risk. 

So a total of 35 women (who, on average, were 36 years old) who regularly slept seven to nine hours a night completed this two-part study. For six weeks, they followed their regular sleep schedule. For another six weeks, they had their bedtime delayed by an hour and a half (bringing their sleep time to about six hours a night). 

Everyone wore a tracker on their wrist to monitor their sleep. At the end of each six-week period, researchers also collected endothelial cells—looking for indicators of oxidative stress.