A new study from the researchers at the Brigham and Women's Hospital has revealed that irregular sleep patterns could be adversely affecting the cardiovascular health of an individual. Their study titled, "Actigraphy-measured Sleep Regularity and Risk of Incident Cardiovascular Disease: The Multi-Ethnic Study of Atherosclerosis," was published in the latest issue of the Journal of the American College of Cardiology.
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For this study, the team measured sleep timings and duration among the participants over five years and noted that the risk for cardiovascular disease rose by two folds among those who slept poorly.
The authors of the study explained that there had been several studies that linked irregular sleep patterns among night shift workers and raised risk of heart disease. They said that this alteration of the circadian rhythm in the general population and shift workers had been studied, but no studies are looking at the association of long term irregular sleep patterns in a prospective manner.
Tianyi Huang, ScD, of Brigham's Channing Division of Network Medicine, the principal author of the study, explained in a statement, "When we talk about interventions to prevent heart attacks and stroke, we focus on diet and exercise. 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. Our study indicates that healthy sleep is not just about quantity but also variability and that this can have an important effect on heart health."
For this study, the team of researchers included 1,993 participants who belonged to the Multi-Ethnic Study of Atherosclerosis (MESA) cohort group. These participants were asked to wear an actigraphy device on their wrists for a week to look at their sleep timings and durations at home. The quality of sleep was monitored between 2010 and 2013, and the participants were followed up until 2015. The participants did not have cardiovascular disease at the start of the study. They were variedly distributed according to ethnicity and race with 38 percent whites, 28 percent African Americans, 22 percent Hispanics and 12 percent Chinese Americans. The participants were aged between 45 and 84 years and belonged to six different centers across the United States.
Over seven days, the team used the activity tracker looked at sleep timings and durations. Over the five years follow up, they looked for cardiovascular diseases such as coronary heart disease, stroke, congestive heart failure, and death due to cardiovascular disease. Other factors that could raise the risk of cardiovascular disease were also taken into account lest they influence the results of the study. Among the factors that affected cardiovascular disease risk were lifestyle factors, sociodemographic factors, and biomarkers of cardiovascular disease. Sleep-related factors that could influence the results included average sleep duration, symptoms of insomnia, sleepiness, or drowsiness during the day, disordered breathing during sleep, irregular work schedules, and missing out on sleep.
Over the 4.9 years of follow up of the participants, there were a total of 95 participants who suffered a cardiovascular event, which included heart attacks and strokes.
Results revealed that compared to those who had sleep duration differences of less than 60 minutes, those that slept between 61 and 90 minutes, 91 and 121 minutes, and over 120 minutes had a lowered risk of cardiovascular disease. With each hour increase in variation in the sleep duration every night, there was a 23 percent raise risk of cardiovascular disease. The risk of heart disease was 87 percent greater among those who went to bed each night with a variation of more than 90 minutes compared to those who had variations of less than 90 minutes, the team found. The team wrote, "These associations did not differ significantly by age, sex, race/ethnicity, sleep duration or work schedules. The exclusion of current shift workers yielded similar results."
They calculated that for every 1,000 participants who had most regular sleep patterns (defined as less than 1-hour difference in the total sleep duration each night), there would be eight individuals who would have a cardiovascular event in one year. On the other hand, for those with most irregular sleep patterns (defined as a difference of two hours or more in the sleep duration each night) for every 1,000 participants, 20 would experience a cardiovascular event over one year.
Conclusions and Future directions
The team wrote in 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."
Huang said, "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."
This study was supported by the National Heart, Lung and Blood Institute and National Center for Advancing Translational Sciences.
Tianyi Huang, Sara Mariani, Susan Redline, Sleep Irregularity and Risk of Cardiovascular Events: The Multi-Ethnic Study of Atherosclerosis, Journal of the American College of Cardiology, Volume 75, Issue 9, https://doi.org/10.1016/j.jacc.2019.12.054.