Abstract

Background: Prior studies have linked rotating night shift work to increased risk of cardiovascular disease (CVD). Irregular sleep schedules, characterized by high day-to-day variability in sleep duration or timing, represent possibly milder but much more common/chronic disruption of circadian rhythms in the general population. However, no prospective study to date has examined the association between sleep regularity and CVD outcomes.

Methods: In the Multi-Ethnic Study of Atherosclerosis, 1,993 participants who were free of CVD completed 7-day wrist actigraphy at home for objective monitoring of sleep duration and quality between 2010 and 2013, and were prospectively followed through 2015. We assessed sleep regularity using the standard deviation (SD) of actigraphy-measured sleep duration and sleep onset timing across 7 days. Incident CVD was defined as total cardiovascular events including coronary heart disease, stroke, congestive heart failure, and cardiovascular death. Cox proportional hazards model was used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for incident CVD according to SD of sleep duration and timing, adjusted for traditional CVD risk factors (e.g., sociodemographic factors, lifestyles and CVD biomarkers) and other sleep-related factors (e.g., average sleep duration, insomnia symptoms, daytime sleepiness, sleep-disordered breathing, chronotype and work schedules).

Results: During a median follow-up of 4.0 years, 95 participants developed CVD events. Compared to participants with a 7-day sleep duration SD ≤60 min, the multivariable-adjusted HR (95% CI) for CVD was 1.12 (0.61, 2.07) for 61-90 min, 1.71 (0.94, 3.09) for 91-120 min, and 2.20 (1.22, 3.96) for >120 min. Every 1-hour increase in sleep duration SD was associated with 23% higher CVD risk (95% CI: 1.05, 1.45; p-trend=0.01). In contrast to this linear association with sleep duration variability, there appeared to be a threshold pattern for the association with SD of sleep onset timing. Compared to participants with a sleep timing SD ≤30 min, the multivariable-adjusted HR (95% CI) for CVD was 1.13 (0.60, 2.13) for 31-60 min, 1.15 (0.58, 2.31) for 61-90 min, and 2.07 (1.09, 3.94) for >90 min. CVD risk was 87% higher comparing sleep timing SD >90 min versus ≤90 min (95% CI: 1.19, 2.96; p=0.007). These associations did not differ significantly by age, sex, race/ethnicity, sleep duration or work schedules. Exclusion of current shift workers yielded similar results.

Conclusion: Irregular sleep duration and timing may be novel risk factors for CVD, independent of traditional CVD risk factors and sleep quantity/quality. Given the increased prevalence of irregular sleep (e.g., due to mobile device use), our findings have important public health implications for CVD prevention and suggest value in evaluating the impact of sleep hygiene interventions aimed at improving sleep pattern consistency.