A Mysterious Link Between Sleeplessness and Heart Disease

By RONI CARYN RABIN
25 dec 2008--People who don’t get much sleep are more likely than those who do to develop calcium deposits in their coronary arteries, possibly raising their risk for heart disease, a new study has found.

The 495 participants in the study filled out sleep questionnaires and kept a log of their hours in bed. At night they also wore motion-sensing devices around their wrists that estimate the number of hours of actual sleep. At the beginning, none of the participants, who were ages 35 to 47, had evidence of coronary artery calcification.

Five years later, 27 percent of those who were sleeping less than five hours a night on average had developed coronary artery calcification for the first time, while only 6 percent of those who were sleeping seven hours or more had developed it. Among those who were sleeping between five and seven hours a night, 11 percent had developed coronary artery calcification, the study found.

After accounting for various other causes, the researchers concluded that one hour more of sleep per night was associated with a 33 percent decrease in the odds of calcification, comparable to the heart benefit gained by lowering one’s systolic blood pressure by 17 millimeters of mercury.

The study was published on Tuesday in the Journal of the American Medical Association. The data were drawn from the ongoing Coronary Artery Risk Development In Young Adults study.

Senior author Diane S. Lauderdale cautioned that the new report does not prove a cause-and-effect relationship between a lack of sleep and heart disease.

“It’s important to say that this is the first report and this does not yet prove the association is causal,” said Dr. Lauderdale, an associate professor of health studies at the University of Chicago Medical Center. “Until we know what the mechanism is -- that it’s really a direct or a causal relationship -- there is no point in making recommendations based on this.”

Although a number of studies have suggested that people who sleep less are at greater risk of heart disease and death, this is the first investigation to measure how much its subjects actually are sleeping, said Dr. Sanjay Patel, assistant professor of medicine at Case Western Reserve University and expert in sleep medicine. Patients’ own self-assessments can be very inaccurate, he added.

What isn’t clear is whether reduced sleep triggers physiological changes that increase heart disease risk, or whether a third, unrelated factor causes both changes, he said.

“It’s possible, for example, that people who are under more stress may be both sleeping less and at higher risk of heart disease,” Dr. Patel said.

If so, he added, “If we got those people to sleep more but they still were under a lot of stress, it wouldn’t change their risk of heart disease.”

Higher education levels are also associated with both a lower risk of heart disease and a tendency to get more sleep, said Dr. Lauderdale.

But it is also possible that lack of sleep leads to certain changes, like increasing blood levels of the stress hormone cortisol, which can raise the risk of coronary artery disease over time, Dr. Lauderdale said.

Another possible mechanism could be through the effect that sleep has on average blood pressure levels over a 24-hour period. Blood pressure usually dips when people are asleep, which could provide health benefits for those who get more sleep, Dr. Lauderdale suggested.