Yana Svetlichnaya, M.D. reports:

CHICAGO - A new study suggests too much or too little sleep can hurt your heart.

People who sleep less than six hours a night are twice as likely to have a stroke or heart attack and one-and-a-half times more likely to have congestive heart failure, while people who sleep more than eight hours a night are more likely to have chest pain and coronary artery disease - a narrowing of the blood vessels that supply blood and oxygen to the heart.

The findings are part of a study presented today at the 61st Annual conference of the American College of Cardiology in Chicago.

"Based on these findings, it seems getting six to eight hours of sleep everyday probably confers the least risk of cardiovascular disease over the long term," said study author Dr. Rohit Arora, chair of cardiology at Chicago Medical School.

Not sleeping enough activates the part of your nervous system responsible for the"fight-or-flight" response releasing high levels of stress hormones that raise your blood pressure, heart rate and blood sugar, all of which are inherently bad for your heart.

Teasing out the harmful effects of too much sleep is more complicated. But some studies suggest people who oversleep may be more likely to have depression and less likely to exercise, which could up the risk of heart disease.

Although Arora's study is not the first study to show that sleep is beneficial, it is one of the largest. The findings support a compilation of studies on sleep between 1980 and 2009 recently published in the European Heart Journal that also concluded sleeping too little or too much raises your risk of dying from coronary artery disease and stroke.

"Sleep has a large impact on health over long periods of time," said Dr. C. Noel Bairey-Merz, director of women's health center at Cedars-Sinai Medical Center in Los Angeles.

Six percent of US adults report sleeping six hours or less, according to National Health Interview Survey between 1984 and 2000.

Experts say the study should serve as a wake-up call for doctors to start asking patients about their sleep habits and for patients to bring up sleep quality with their doctors.

The importance of sleep to patients "is no longer worth ignoring," said Dr. Robert Eckel, professor of medicine and Charles A Boettcher II Chair of Atherosclerosis at the University of Colorado.

Dr. Svetlichnaya is an internal medicine resident at Northwestern University's McGaw Medical Center.