A new study published in the Journal of the American Medical Association suggests that not getting enough sleep might leave you more than cranky – it might also lead to hardening of the arteries, an early step to heart disease.

The study, which followed new cases of coronary artery calcification among nearly 500 middle-aged US adults over a five-year period, found that people who slept five to seven hours nightly were almost twice as likely as those who slept longer to develop early blood-vessel damage that may lead to heart problems.

“There’s mounting evidence that really short sleep duration, as in less than five hours a night, may well have health consequences. It’s pretty safe to say that it’s a good idea to get more than five hours of sleep a night,” said Diane Lauderdale, the University of Chicago epidemiologist who led the research team.

At the beginning of the study none of the participants had detectable calcium deposits, but five years later, 61 (12.3 percent) did. Calcium deposits can make the coronary arteries less flexible and ultimately lead to heart disease.

The study found that after adjusting for lots of potential risk factors, such as sex, race, and smoking habits, 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.

There are some explanations for these findings. Firstly, there may be some factor not yet identified that can both reduce sleep duration and increase calcification. Or, it’s a known fact that less sleep leads to high blood pressure which increases the likelihood of calcification and blood pressure goes down during sleep.

Also, stress or a stress hormone like cortisol, which has been tied to decreased sleep and increased calcification, may play a role.

“Although there are constant temptations to sleep less, there is a growing body of evidence that short sleep may have subtle health consequences. Although this single study does not prove that short sleep leads to coronary artery disease, it is safe to recommend at least six hours of sleep a night,” Lauderdale said.

The study is the more important as heart disease is the number one killer in the United States. More and more people are suffering from high blood pressure, the first sign of heart disease.

High blood pressure is a serious condition that can lead to coronary heart disease, heart failure, stroke, kidney failure and other serious health problems. There are several risk factors that contribute to hypertension, such as smoking, alcohol use, excessive salt in diet, sedentary lifestyle, obesity and family history. Lack of sleep seems to be another major reason of concern when it comes to high blood pressure and heart disease.

According to recent estimates, about one in three U.S. adults has high blood pressure, but because sometimes there are no symptoms, nearly one-third of these people are unaware they have it.