MILWAUKEE — People in their 30s and 40s who got less sleep at night were more likely to develop the early buildup of plaque in the arteries of their heart, according to a provocative new study.
The study is the first to link an objective measure of the duration of a person's sleep to an established method for assessing the risk of coronary artery disease, a CT scan that measures calcification in the arteries.
"Science is once again confirming a commonly held belief — an anecdote of our common knowledge — sleep matters," said Richard Staudacher, a cardiologist with ProHealth Care Medical Associates Cardiology in Waukesha, Wis. "When our parents and health teachers told us that sleep was important … they were right, and we are now finding out why."
The study involved 495 healthy people ages 35 to 47 who did not have artery disease and who were followed for five years.
At the beginning of the study, they had a CT scan that looked for the presence of calcium in their arteries, a known risk factor for heart disease. Their sleep patterns were measured using a wrist device that senses movement and is considered an objective measure of the amount a sleep obtained during the night.
At the end of the study, they underwent a second CT scan. A total of 12.3 percent of the subjects had developed at least some calcification in their arteries, a sign of early heart disease. The study was published last week in the Journal of the American Medical Association.
On average, those in the study got about six hours of sleep a night.
However, only 6 percent of those who got at least seven hours of sleep had calcification, compared with 11 percent who got five to seven hours and 27 percent who got less than five hours, said the senior author, Diane Lauderdale, an associate professor of health studies at the University of Chicago.
The study took into account other known risk factors for heart disease, including sleep apnea, cholesterol, blood pressure, body weight, diabetes and depression.
In fact, getting an extra hour of sleep had the same effect on heart disease risk as lowering one's systolic blood pressure (the upper reading) by 16.5 points.
The study adds to the mounting evidence that short sleep duration (less than five hours) has subtle health consequences, Lauderdale said.
Indeed, over the last several years, research has shown the length of time a person sleeps is important to health, said Terry Young, a sleep expert with the University of Wisconsin School of Medicine and Public Health.
Some of the research suggests a U-shaped curve with too much and too little sleep being implicated in health problems, she said. However, too much sleep may be the result of people already having health problems. So studies such as the JAMA article, which focus on a lack of sleep, are important, said Young, who was not a part of the study.
"Knowing what sleep disruption does to the sympathetic nervous system, it's hard to imagine it would not have an impact on the cardiovascular system," said Young, a professor epidemiology.
B. Tucker Woodson, a sleep specialist at the Medical College of Wisconsin who was not a part of the study, said he was surprised at the magnitude of the effect given that the study lasted only five years and the volunteers were healthy people in their 30s and 40s. "What happens over 10 years in people who are less healthy?" he said.
A big question that the study did not answer was how could a lack of sleep contribute to calcium buildup in coronary arteries?
Since the study was adjusted to take into account sleep apnea, a type of interrupted breathing during sleep that is known risk factor for heart disease, doctors said the cause likely was some other process.
One possibility is that a lack of sleep leads to higher levels of cortisol, a stress related hormone made in the adrenal glands that is associated with a wide range of metabolic abnormalities such as increased glucose in the blood and inflammation in the body.
Woodson, chairman of the division of sleep medicine at the Medical College, said he and others at the college did a small study involving people with sleep apnea who got a breathing device at night or a placebo. Those who got the breathing device and who got more sleep had lower levels of cortisol, he said.
"Sleep seems to affect the body's ability to control glucose and cortisol," said Woodson.
Staudacher, of ProHealth Care, said it is possible that a lack of sleep contributes to hormonal changes that damage the lining of blood vessels. "This was a little surprising," he said. "Over a short period of time you would not expect to see much (increase in calcium in the arteries)."
Study author Lauderdale said another possibility is that a lack of sleep leads to unhealthy blood pressure changes at night.
She said more studies are needed to measure a connection over time between a lack of sleep and actual events such as heart attacks.