THURSDAY, Sept. 10, 2015 (HealthDay News) -- Otherwise healthy people who have poor sleep habits may be putting themselves at risk for early signs of heart disease, a new study suggests.

Folks who get too much or too little sleep -- or not enough quality rest -- are more likely to suffer from stiffened arteries and calcium deposits on the walls of their major arteries, said study lead author Dr. Chan-Won Kim.

"Coronary calcium develops way before heart attack symptoms occur, and a greater amount of calcium in the coronary arteries predicts future development of heart disease," said Kim, a clinical associate professor in the Center for Cohort Studies at Kangbuk Samsung Hospital in Seoul, South Korea.

The sweet spot appears to be about seven hours of sleep, the researchers reported. People who got more or less sleep tended to have increased signs of potential future heart problems.

Earlier studies have linked poor sleep to bad heart health, but this research goes a step further by looking for precursors of heart disease in people who appear healthy, said Dr. David Meyerson, a cardiologist at Johns Hopkins Bayview Medical Center in Baltimore and a national spokesman for the American Heart Association.

Because the study authors took this route, their implications more directly highlight sleep as a potential risk factor for heart disease, Meyerson said.

"Quality and duration of sleep is not always asked by every physician during a cardiovascular risk assessment session, and perhaps it should be," he said.

While the study uncovered a link between poor sleep and potential heart problems, it did not prove a cause-and-effect connection.

The study involved more than 47,000 young and middle-aged adults who completed a sleep questionnaire and had advanced tests to measure arterial stiffness and detect early artery lesions caused by calcium deposits.

The findings revealed that study participants who:

• got five or fewer hours of sleep a day had 50 percent more calcium in their arteries than those who slept seven hours a day.
• slept nine or more hours a day had at least 70 percent more calcium compared to those who slept seven hours.
• reported poor sleep quality had more than 20 percent more calcium than those who reported good sleep quality.

"Since we studied apparently healthy young and middle-age men and women without major diseases, it is unlikely that other health problems can explain the association between extreme sleep duration and early markers of heart disease," Kim said.

Doctors don't yet know exactly why the proper amount of sleep appears to protect heart health, said Meyerson and Dr. Mark Urman, a cardiologist with Cedars-Sinai Heart Institute in Los Angeles.

During sleep, a complex dance of metabolic changes, hormone releases, body repair and brain refreshment takes place. These processes affect blood pressure, blood sugar, inflammation, stress hormones and a host of other factors that can increase risk of heart disease, the cardiologists said.

"We know our bodies every day need this ability to recharge our batteries, to put everything at ease and calm everything down," Urman said, adding that poor sleep has been linked to heart risk factors like diabetes and obesity.

Sleep should be considered part of an overall heart-healthy lifestyle, Urman said.

"This adds to the importance of getting a good night's sleep on a regular basis, in addition to regular exercise and a heart-healthy diet, in reducing risk of heart disease," he said. "This is one more thing that's part of that package."

People who want to improve their sleep should dim the lights in their living room or bedroom as bedtime approaches, and they should go to bed at the same time every day, Kim said.

"It is also important to avoid exposure to electronic media at bedtime," Kim said. He added that "people who experience inadequate sleep need to avoid caffeine-containing beverages after lunch."

The study findings were published Sept. 10 in the American Heart Association journal Arteriosclerosis, Thrombosis and Vascular Biology.

More information

For tips on getting a good night's sleep, visit the Harvard Medical School.