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Sleep to Your Heart's Content
Abstract & Commentary
By Joseph E. Scherger, MD, MPH, Clinical Professor, University of California, San Diego. Dr. Scherger reports no financial relationship to this field of study.
Synopsis: A prospective study of men and women showed that duration of sleep is correlated with coronary artery calcification with 1 hour more of sleep daily reducing the odds of calcification over 5 years by 33%.
Source: King CR, et al. Short sleep duration and incident coronary artery calcification. JAMA 2008;300:2859-2866.
A group of investigators at the University of Chicago are following a cohort of 495 men and women, black and white, over many years looking at risk factors for the development of coronary artery disease. They are the Coronary Artery Risk Development in Young Adults (CARDIA) cohort. At year 15 of the study, in 2000-2001, at ages 35-47, this group underwent CT scanning for coronary artery calcification. The CT scanning was repeated in 2005-2006. Sixty-one (12.3%) had developed coronary artery disease during this 5-year period.
Controlling for age, sex, race, education, apnea risk, smoking status, lipid levels, blood pressure, body mass index, diabetes, inflammatory markers, alcohol consumption, depression, hostility, and self-reported medical conditions, duration of sleep demonstrated an impact on the development of coronary artery calcification. The duration of sleep was objectively measured using a wrist activity monitor that the participants wore for 6 nights during 2 different waves of measurement 1 year apart. The objective measurements roughly correlated with self-reported sleep duration.
Sixty-six (13.3%) of the 495 participants had a sleep duration of less than 5 hours per night and had a 5-year incidence of development of coronary artery calcification of 4%-9.5% depending on the duration sleep. The largest number (336, 67.9%) had sleep durations between 5 and 7 hours with a 5-year incidence of developing coronary artery calcification of about 2%. For the 93 participants (18.8%) with sleep duration of 7 hours or more, the incidence of developing coronary artery calcification was 0-1.5%, depending on the duration of sleep. One hour more of sleep reduced the estimated odds of developing coronary artery calcification by 33%.
Sleep is regarded as a "fourth pillar" of good health along with not smoking, good nutrition, and exercise. Understanding the importance of sleep to health, and the problems associated with poor sleep, has emerged over the past couple of decades. This cohort study of young to middle-aged adults used a novel method to objectively measure sleep duration and found that a lack of at least 5 hours of sleep substantially increases the risk of development of coronary artery calcification, a marker for coronary artery disease. Although the numbers were small, getting 7 hours of sleep or more each day seems to offer major protection from coronary artery calcification, controlling for other risk factors.
This cohort study offers suggestive evidence but is not definitive in proving that sleep protects against the development of coronary artery disease and that the lack of it is a cardiac disease risk factor. Other risk factors such as smoking and diabetes have a greater impact on the development of coronary artery calcification than sleep duration. The study shows that sleep and coronary artery calcification are inversely related. Now we have more evidence of the importance of sleep to health and the potential danger to the heart of being deprived of a good night's sleep on a regular basis.