According to a study published in the December 24/31 issue of JAMA,
sleeping an hour longer each night may lead to a lower incidence of
coronary artery calcification – a predictor of future heart disease.

Coronary
artery calcification is characterized by an accumulation of calcium
plaques that detected computed tomography scans of the heart. As a risk
factor for atherosclerotic heart disease, coronary artery calcification
also shares many of the same risk factors for heart disease including:

Being male
Being older
Glucose intolerance
Tobacco use
High cholesterol levels and other disorders of lipoprotein
metabolism (dyslipidemia)
Hypertension (high blood pressure)
Obesity
Raised inflammatory markers
A low educational level

In
some recent studies, sleep quantity and quality has been found to be
related to several of these risk factors. “However, some of
these
correlations have only been documented in studies in which sleep is
measured by self-report, which may be biased or insufficiently
accurate,” write the authors of the study.

To test if an
objectively-measured sleep duration was linked to the development of
calcification over a 5 year period, Christopher Ryan King, B.S.
(University of Chicago) and colleagues conducted a study with 495
individuals. The participants were part of the Coronary Artery Risk
Development in Young Adults [CARDIA] study, a sample of black and white
men and women between the ages of 35 and 47. The study began in
2000-2001, a time in which none of the participants demonstrated
evidence of detectable coronary calcification on computed tomography
scans.

Baseline data and follow-up data were collected on
factors that could potentially make it more difficult for the
researchers to tease out the effect of sleep. These possible
confounders included age, sex, race, education, apnea risk, smoking
status, lipids, blood pressure, body mass index, diabetes, inflammatory
markers, alcohol consumption, depression, hostility, and other
self-reported medical conditions. Measurements of sleep duration, sleep
fragmentation, daytime sleepiness and overall sleep quality were
provided by wrist actigraphy (a tool that monitors rest and activity)
and self-reports. The researchers focused the study on the effect that
these sleep metrics had on new calcification as detected by computed
tomography scans in 2005-2006.

Results indicated that 12.3% (61
participants) developed calcification after 5 years. After
controlling for confounding factors like age, sex, race, education,
smoking and apnea risk, the researchers report that one additional hour
of sleep per night lowered the estimated odds of calcification by 33%.
In addition, the magnitude or significance of sleep was not appreciably
altered by potential mediators. Sleep metrics other than duration did
not appear to be significantly linked to the risk of calcification.

“We
have found a robust and novel association between objectively measured
sleep duration and 5-year incidence of coronary artery calcification,”
write King and colleagues. “This study further demonstrates the utility
of a simple objective measure of sleep that can be used at home. Future
studies will be needed for crucial extensions to these results. First,
these results need confirmation in other cohorts. Second, does sleep
moderate the rate at which calcification accumulates? Third, will
objective sleep tie to coronary disease event outcomes over the long
term? While calcification predicts such outcomes, it is difficult to
know how and if the predictors of calcification themselves will
determine outcomes, or if their impact will be purely mediated by their
effect on calcification. Finally, if this association is born out,
interventional studies will be needed to guide clinical advice.”

Short Sleep Duration and Incident Coronary Artery Calcification
Christopher Ryan King; Kristen L. Knutson; Paul J. Rathouz; Steve
Sidney; Kiang Liu; Diane S. Lauderdale
JAMA (2008). 300[24]:
pp. 2859-2866.
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: Peter M Crosta