Introduction and Objectives: Experimental research suggests that sleep deprivation may alter physiological factors associated with an increased risk for cardiovascular diseases (CVDs). Prior observational studies examining the effects of sleep duration have focused on narrowly defined CVD outcomes, such as myocardial infarction or stroke only. A more comprehensive measure of CVDs is lacking. Therefore, we examined the relationship between sleep duration and Major Adverse Cardiac Events (MACE).

Materials and Methods: In 1997, 39,047 Swedish residents (women: 64%, age: 18-94 years) were enrolled in the National March cohort study and asked to self-report their habitual sleep duration in a questionnaire. They were followed-up over approximately 7 years to study incidents of MACE. Events were defined as death from all CVDs, nonfatal myocardial infarction, stroke, or heart failure. The relationship between sleep duration and MACE was analyzed using Cox proportional hazards models.

Results: A total of 1,730 events were observed during a median follow-up period of 7.25 years. We found 665 nonfatal myocardial infarctions, 641 nonfatal strokes, 212 nonfatal heart failures, and 198 deaths from all CVDs. Age- and sex-adjusted hazard ratios (95% confidence intervals) of MACE (with 7 hours of sleep/day as the reference group) for individuals reporting ≤5, 6, and ≥ 8 hours of sleep were 1.24 (1.05-1.47), 1.03 (0.91-1.16), and 1.09 (0.97-1.23), respectively. Adjusting for BMI and physical activity did not change the hazard ratios. When adjusting for additional confounders, e.g., depressive symptoms, sleep apnea, and smoking, the association between ≤5h of sleep and MACE was attenuated (HR: 1.22, 95% CI: 0.98-1.52).

Conclusion: Sleep duration was not associated with the risk of Major Adverse Cardiac Events. Sleep duration, however, may not in itself explain the effects of inadequate sleep on cardiovascular diseases. Yet, it may serve as an essential component in the understanding of cardiovascular diseases. Copyright © 2011 Elsevier B.V. All rights reserved.