Skipping Sleep May Signal Problems For Coronary Arteries
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. The benefit of one hour of additional sleep was comparable to
the gains from lowering systolic blood pressure by 17 mm Hg.
percent of those in the study, healthy volunteers in their 40s, 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 six 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.
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."
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.
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.
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.
filled out sleep questionnaires, kept a log of their hours in bed and
participated in 6 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.
In a previous
study, Lauderdale and colleagues used actigraphy and nightly logs to
study, on average, how long people spent in bed (7.5 hours), how long
it took them to fall asleep (22 minutes), how long they slept (6.1
hours), and their total sleep efficiency--time asleep divided by time
trying to sleep in bed (81 percent).
they looked at the connections between sleep duration and coronary
artery calcification. They found more than they anticipated.
studies have correlated decreased sleep times with established risk
factors for calcification, including high blood pressure, excess
weight, and poor glucose regulation. But in this study, "after
adjusting for age, sex, race, education, smoking, and apnea risk," the
authors note, "longer measured sleep duration was associated with
reduced calcification incidence."
suggest three possible ways that shorter sleep could connect to
calcification. First, there may be some factor not yet identified that
can both reduce sleep duration and increase calcification. Second,
although blood pressure measured during examinations did not seem to
explain the association, blood pressure generally declines during
sleep, so the 24-hour average blood pressure of those who sleep less
may be higher, and that could lead to calcification. Finally, stress or
a stress hormone like cortisol, which has been tied to decreased sleep
and increased calcification, may play a role. Cortisol data were not
available for all study participants.
"This was a
small study and a new finding, so we would love to see it duplicated in
another study population," Lauderdale said. "But there is enough here
to make a point. Although there are constant temptations to sleep less,
there is a growing body of evidence that short sleep may have subtle
health consequences. Although this single study does not prove that
short sleep leads to coronary artery disease, it is safe to recommend
at least six hours of sleep a night."
The study was supported by grants from the National Heart, Lung and Blood Institute and the National Institute on Aging.
For more information on the University of Chicago Medical Center, visit www.uchospitals.edu.