If you sleep too little, or even too much, you might be doing a lot of damage to your heart. A new study published in Arteriosclerosis, Thrombosis and Vascular Biology finds that either of these factors in young to middle-age people – along with poor quality of sleep – raises levels of calcium in the coronary arteries, leading to arterial stiffness.
Researchers in South Korea discovered that men and women who slept for 9 or more hours a day had more calcium in their arterial walls and stiffer arteries than those who slept 7 hours a night. Higher calcium in the arterial walls and stiff arteries are both contributing factors for heart disease. 
People that get poor-quality sleep are at risk, too.
The scientists found that people who said they slept poorly were more likely to have these two early signs of heart disease than those who said they slept better. 
“Many people, up to one third or one fourth of the general population, suffer from inadequate sleep – either insufficient duration of sleep or poor quality of sleep,” said co-lead author Dr. Chan-Won Kim of Kangbuk Samsung Hospital of Sungkyunkwan University School of Medicine in Seoul, South Korea.
Inadequate sleep has been linked with a higher risk of heart attack and stroke in the past, but in an e-mail to Reuters, Kim explained that other health issues like depression or obesity could influence this association.
“In contrast, we studied if sleep of inadequate duration or quality would be linked to early markers of heart disease in asymptomatic healthy adults free of heart disease,” Kim said
More than 47,000 men and women filled out questionnaires about their quality of sleep for the study. Researchers also conducted tests to detect lesions of calcium and plaque on the walls of the arteries leading to the heart, as well as arterial stiffness in the leg. The presence of calcium and plaque indicates early heart disease; arterial stiffness is a sign of vascular aging.
The participants, age 42 on average, had an average sleep duration of 6.4 hours per night, with about 84% reporting that their sleep quality was good. People who slept 5 or less hours per night were categorized as “short” sleepers by researchers, and people who slept 9 or more hours were categorized as “long” sleepers.
Fifty percent more calcium was found in the arteries of short sleepers than those who snoozed 7 hours a night, and 70% more calcium was observed in long sleepers than people who slept 7 hours. 
People who responded that they slept poorly also tended to have more calcium in their arteries and arterial stiffness.
“The calcium score obtained by computerized tomography scan is a very good measure of calcium buildup in the coronary arteries reflecting coronary atherosclerosis,” Kim said. “The higher the coronary calcium score, the greater the risk of having a heart attack in the future.
It is still not clear if inadequate sleep is the cause or the consequence of ill health,” but good sleep hygiene, including avoiding electronic media at bedtime, should be part of a healthy lifestyle.
For doctors, it can be helpful to evaluate sleep duration and sleep quality when assessing the health status of their patients,” Kim said.
The study showed a “U-shaped curve” between sleep duration and calcium in the arteries and arterial stiffness, indicating that neither extreme is a healthy one.
Heart disease and diseases of the blood vessels, such as hormone disturbances and inflammation, have been consistently linked to sleep disturbances. And plenty of other studies have linked too much or too little sleep with higher rates of strokes, heart disease and even death.