It's true — hard work really can kill you. Working more than 45 hours a week over the course of 10 years raises your risk of heart disease, says a study from The University of Texas Health Science Center at Houston.

Researchers studied the data from 1,999 full-time workers who had been employed for at least 10 years. They found that averaging 46 hours or more a week increased the long-term risk for cardiovascular disease (CVD).

"In general, we found that the risk of CVD increased as the average weekly working hours increased, above a certain threshold," said lead author Sadie H. Conway, Ph.D. The study found that among full-time workers, the risk of heart disease was lowest in those who worked between 40 and 45 hours per week.

People who worked 55 hours a week increased their cardiac risk by 16 percent, and those who averaged 60 hours a week were 35 percent more likely to suffer cardiovascular disease.

Although other studies have indicated a link between cardiovascular disease and long working hours, the new study was the first to identify and quantify a "dose-response" effect.

"This study provides specific evidence on long work hours and an increase in the risk of CVD, thereby providing a foundation for CVD-prevention efforts focused on work schedule practices, which may reduce the risk of CVD for millions of working Americans," said Conway.

Heart disease is the No. 1 cause of death in the U.S., claiming more than 610,000 lives every year, more than all types of cancer combined, according to the Centers for Disease Control and Prevention.

The study was published in the Journal of Occupational and Environmental Medicine.