Irregular sleep patterns can double heart disease risk, study suggests
A newly published study from researchers at Brigham and Women’s Hospital in Boston is suggesting irregular sleep patterns, such as inconsistent bedtimes from day to day, can potentially double a person’s risk of developing cardiovascular disease.
"When we talk about interventions to prevent heart attacks and stroke, we focus on diet and exercise," says Tianyi Huang, lead author on the new study. "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.”
A great deal of recent research has affirmed the importance of sleeping a solid eight hours every night. Too little sleep can increase your risk of diabetes, too much sleep has been linked to stroke, and optimal cognitive performance during the day can be tied to an ideal duration of sleep. But how much of an effect do irregular sleep patterns have on a person’s health? Are the benefits of a solid eight hours undercut if you go to sleep at different times every night?
A 2019 study from Brigham and Women’s Hospital raised this possibility after evaluating data from a long-term research project called the Multi-Ethnic Study of Atherosclerosis (MESA). Part of the study involved participants recording sleep patterns across a seven-day period using an activity tracking wearable device. The participants general health was then followed for an average of five years.
Last year’s study revealed those subjects with the greatest variation in bedtimes from night to night were more likely to develop metabolic disorders such as hypertension, obesity and diabetes. The new study is now presenting an association between irregular sleep patterns and cardiovascular events.
The most irregular sleep patterns determined in the new study were defined as bedtimes differing by 90 minutes or more each night, and sleep durations varying by two hours or more each night. Those subjects with these these most irregular sleep patterns displayed nearly double the amount of cardiovascular events across the five year follow-up period, compared to those subjects with the most consistent sleep patterns.
“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,” says Huang.
While the research is undeniably compelling and novel, it does suffer from the same limitations as last year’s study. Data gathered from self-reported sleep diaries and questionaries is notoriously inconsistent, and the participants’ sleep patterns were only objectively tracked for a seven-day stretch at the beginning of the study. So, it is unclear how consistent these irregular sleep patterns were across the entire five-year study.
The study is also not designed to offer insight into causal connections between irregular sleep patterns and cardiovascular health. It could be that variable bedtimes and inconsistent sleep durations are symptoms of other harmful lifestyle behaviors that are causing the negative health consequences.
The researchers do hypothesize consistent circadian rhythm disruptions as the potential causal mechanism resulting in the increased risk of cardiovascular events. Other recent research has indeed found links between metabolic disease and circadian rhythm disruptions, so this hypothesis is not a stretch. However, further work is certainly needed to better understand the correlation uncovered in this new study.
"Sleep regularity is a modifiable behavior,” says Huang. “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.”
The new study was published in the Journal of the American College of Cardiology.