The Washington Post reports that a new five-year study has found that more sleep can reduce calcium deposits in people’s arteries. Specifically, the study found that people getting one extra hour of sleep each night were less likely to have “artery-stiffening calcium deposits.” The researchers do not know why there is a link between more sleep reduced calcium deposits but they do have theories involving cortisol and reduced blood pressure.

After adjusting for lots of potential risk factors, such as sex, race, and smoking habits, the researchers found that one more hour of sleep a night decreased the risk of calcification by a third. That’s about as much as a 16.5-point reduction in blood pressure, the researchers said.

“Nothing came out of the study as appearing to explain the association,” Lauderdale said. But she believes that there are three possible explanations.

One is that another factor, such as socioeconomic status, was the connection here. A second is that a stress-related hormone, cortisol, which has been tied to decreased sleep and increased calcification, is the link.

“Finally, sleep is related to blood pressure, and that is a coronary artery disease risk factor,” Lauderdale said. “It’s possible that for people who were sleeping more, their 24-hour blood pressure was lower than their daytime blood pressure.”

It’s already been proven that being sleep deprived can be unhealthy so it is best to try to get a full night’s sleep. It’s disturbing news for those who are unable to get a full night’s sleep because of work or health issues. It’s also confusing because no one knows exactly what a full night’s sleep is and the hours of sleep people need varies in individuals. For more on how much sleep you really need read this article from Time that talks about a study that tried to answer this question.