Irregular Sleep Patterns Linked to Two-Fold Increase in Heart Disease

Tianyi Huang, ScD

A new analysis of the Multi-Ethnic Study of Atherosclerosis (MESA) from investigators at Brigham and Women’s Hospital is shedding further light on the relationship between sleep and cardiovascular health.

Results of the study indicated patients with irregular sleep schedules, which investigators defined as 2 or more hours difference in sleep duration each night, was linked to a two-fold increase in the risk of suffering a cardiovascular event over a 5-year period compared to patients with regular sleep patterns.

"Even when we talk about sleep, we tend to focus on duration—how many hours a person sleeps each night—but not on sleep irregularity and the impact of going to bed at different times or sleeping different amounts from night to night,” said lead investigator Tianyi Huang, ScD, of the Brigham's Channing Division of Network Medicine, in a statement. “Our study indicates that healthy sleep isn't just about quantity but also about variability, and that this can have an important effect on heart health."

With an emphasis on the importance of sleep on overall health at an all-time high, Huang and a team of colleagues sought to determine how irregularities in sleep might correlate to a person’s risk of cardiovascular disease (CVD). Using data from the MESA study, Huang and her team conducted an analysis of 1992 individuals free of CVD and completed 7-day wrist actigraphy for sleep assessment.

All patients included wore the Actiwatch Spectrum wrist actigraph on their nondominant wrist for 7 consecutive days and completed a sleep questionnaire that assessed sleep habits and sleep-related traits. The primary endpoint of the trial was a composite of nonfatal and fatal cardiovascular events, which was assessed through MESA follow-up examinations as well as telephone interviews.

Patients were divided into groups based upon sleep duration SD. Those with a sleep duration SD of 60 minutes or less were used as a reference group while the other groups were defined as 61 to 90 minutes, 91 to 120 minutes, and greater than 120 minutes.

Cox proportional hazards model was used by investigators to estimate hazard ratios (HR) for incident CVD according to SD of sleep duration and timing. Huang and colleagues noted their analyses were adjusted for multiple CVD risk factors and other sleep-related factors.

Of the 1992 individuals, 786 had a sleep duration SD greater than 90 minutes and 510 had sleep-onset timing SD of greater than 90 minutes. Investigators noted metallic and sleep-related parameters were generally worse among patients with higher than lower sleep duration SD.

Among the study cohort, a total of 111 incident CVD events over a median of 4.9 years of follow-up, which resulted in an incidence rate of 11.8 per 1000 person-years. Both unadjusted and adjusted analyses indicated a trend toward increased incidence of CVD with more irregular sleep duration, with investigators noting the trend becoming more apparent in the adjusted analyses.

Compared to the reference group, the HR for the SD 61 to 90 minutes group was 1.09 (95% CI, 0.62-1.92), 1.59 (0.91-2.76) for the 91 to 120 minutes group, and 2.14 (1.24-3.68 for the greater than 120 minutes group (P trend=.002) in the adjusted analysis. Additionally, an analysis assessing impact sleep timing SD found the HRs for CVD were 1.16 for 31 to 60 minutes (95% CI, 0.64-2.13), 1.52 for 61-90 minutes (0.81-2.88), and 2.11 (1.13-3.91) for greater than 90 minutes (P trend=.002). Investigators noted these results were similar even after the exclusion of shift workers.

While Huang and colleagues highlighted the indications of study results, they also pointed out multiple limitations within their study. Limitations included modest sample size and inability to exclude residual and unmeasured confounding.

"Sleep regularity is a modifiable behavior. In the future, we'd like to explore whether changing one's sleep patterns by going to bed consistently each night may reduce a person's risk of future cardiovascular events," said Huang, in the aforementioned statement.

This study, "Sleep Irregularity and Risk of Cardiovascular Events,” was published in JACC.