Sleep Duration Linked to Cardiovascular Health

Skimping on sleep may increase the risk of coronary heart disease, an observational cohort study of middle-aged persons showed.

The effect was independent of other risk factors for the buildup of calcified plaques, they reported in the Dec. 24/31 issue of the Journal of the American Medical Association.

Dr. Lauderdale and colleagues were unable to explain the mechanism underlying the association and said that there may be unknown factors that predict both sleep duration and calcification.

Previous studies have found that sleep duration and quality are associated with risk factors for coronary artery calcification, such as glucose regulation, blood pressure, sex, age, education, and obesity, according to the researchers.  But the studies were subject to various limitations, including the use of self-reported sleep measures, they said.

To explore the issue using objective measures of sleep duration and quality, the researchers turned to the Coronary Artery Risk Development in Young Adults (CARDIA) study, an ongoing prospective, multicenter cohort study examining the development of cardiovascular risk factors.

They calculated the five-year incidence of coronary artery calcification in 495 participants from the Chicago study site.  The participants ranged in age from 35 to 47 and were free of calcified plaques at baseline as determined by computed tomography.  Sleep duration and quality were measured using a wrist activity monitor and questionnaires assessing daytime sleepiness, overall quality, and self-reported duration.

Mean sleep duration was 6.1 hours.

Through five years of follow-up, 12.3% of participants showed signs of coronary artery calcification.

The risk of calcified plaque accumulation decreased significantly with each additional hour of objectively measured sleep after adjusting for age, sex, race, education, smoking, and apnea risk (P=0.01).

Additional adjustment for major cardiovascular risk factors had little effect on the results.

There were no significant associations found between incident coronary artery calcification and any of the other sleep metrics -- self-reported sleep (P=0.30), sleep fragmentation (P=0.66), a measure of overall sleep quality and disturbance (P=0.24), and a measure of daytime sleepiness (P=0.10).

Stratification by sex seemed to suggest a stronger effect in women than in men, but the between-group difference was not statistically significant (P=0.12). In addition, the effect did not vary by race (P=0.92) or apnea risk (P=0.51).

The researchers said that "the magnitude of the observed effect was similar to sizable differences in established coronary risk factors."  For example, they said, the modeled effect of one additional hour of sleep was equal to the modeled effect of a 16.5-mm Hg decrease in systolic blood pressure.  Additional factors such as inflammatory biomarkers, fibrinogen and interleukin 6, and cortisol profiles -- for which data were lacking -- may also play a role, they said.
Finally, diurnal variation in calcification pathways may influence the association, they said.

Practice Pearls:
Explain to interested patients that developing coronary artery calcification is not a certain predictor of developing cardiovascular disease
Journal of the American Heart Association; King C, et al "Short sleep duration and incident coronary artery calcification" JAMA 2008; 300: 2859-2866.