One extra hour of sleep per night appears to decrease the risk of coronary artery calcification, an early step down the path to cardiovascular disease, a research team based at the University of Chicago Medical Center reports in the Dec. 24/31 issue of JAMA.

The benefit of one hour of additional sleep was comparable to the gains from lowering systolic blood pressure by 17 mm Hg.

About 12 percent of those in the study, healthy volunteers in their 40's, first developed coronary artery calcification over five years of follow-up. Calcified arteries, however, were found in 27 percent of those who slept less than five hours a night. That dropped to 11 percent for those who slept five to seven hours and fell to 6 percent for those who slept more than seven hours a night.

The benefits of sleep appeared to be greater for women. They did not vary according to race.

"The consistency and the magnitude of the difference came as a surprise," said study director Diane Lauderdale, PhD, associate professor of health studies at the University of Chicago Medical Center. "It's also something of a mystery. We can only speculate about why those with shorter average sleep duration were more likely to develop calcification of the coronary arteries."

Recent studies have suggested that chronic partial sleep deprivation may be a risk factor for an array of common medical problems, including weight gain, diabetes and hypertension. One study found that both long and short self-reported sleep durations were independently associated with a modestly increased risk of coronary events.

This is the first study to link objectively measured sleep duration to a pre-clinical marker for heart disease.

The research focused on 495 participants in the Coronary Artery Risk Development in Young Adults (CARDIA) study. An ongoing project begun in 1985, CARDIA was designed to assess the long-term impact of various factors on the development of coronary artery disease.

Participants underwent two electron beam computed tomography scans, designed to assess the buildup of calcium within the arteries that deliver blood to the heart muscle, five years apart.

They also filled out sleep questionnaires, kept a log of their hours in bed and participated in six nights of sleep studies with a technique called wrist actigraphy that uses a motion sensor--worn like a watch--to estimate actual sleep duration.

This approach provides the most accurate measure of routine sleep behavior without subjecting the volunteers to the unfamiliarity of multiple sensors that determine sleep by monitoring brain activity.

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