Sleep and cardiovascular disease are not two terms generally associated. Sleep duration or quality are rarely listed as risk factors for cardiovascular disease, but a growing body of research suggests that perhaps they ought to be. In order to minimize the risk of cardiovascular disease, it is important to make restful sleep in the right amounts a priority.

Heart Disease: A Rising Threat

The term cardiovascular or heart disease encompasses many different conditions affecting the blood vessels or tissue of the heart. These may include heart valve problems, atherosclerosis (in which plaque builds up in the walls of the arteries and causes clotting), arrhythmias (irregularities in the heartbeat), heart attack, stroke, and heart failure. Every year, cardiovascular disease is responsible for nearly 800,000 deaths in the United States alone. If there is a link between sleep and cardiovascular disease, surely, it is critical to learn more. 

Sweet Dreams: The Importance of a Good Night’s Sleep

Any parent with a small child knows the importance of bedtime, both for the child and for the parent. Sleep provides a critical interval for the body to rest, purge the toxins in the brain, alleviate anxiety, strengthen the immune system, and basically perform a system reset. In our busy world, it is meant to serve as a time of stillness to let our body’s rhythms catch up. In order to do this, the body needs enough time spent in high quality sleep. 

The CDC recommends that people 18 years or older get 7 or more hours of sleep each night. While sleep quality is more difficult to measure than duration, it is a vital part of ensuring a well-rested night. If you wake up and do not feel rested, the health benefits of that interval of sleep are likely to be less potent. Poor quality sleep and cardiovascular disease risk are linked. If you are prone to poor-quality sleep, speak to your doctor. There are many causes of restless sleep—insomnia, sleep apnea, etc.—and treatment must be based on the root.

Studying the Link Between Sleep and Cardiovascular Disease

While the relationship between sleep and cardiovascular disease leaves much room for exploration, a body of research does exist. In 2018, authors Kwak, et al. published a meta-analysis in the Journal of the American Heart Association reporting their findings. Their work, entitled “Self‐Reported Sleep Duration and Quality and Cardiovascular Disease and Mortality: A Dose‐Response Meta‐Analysis,” reviewed the data collected in 74 studies, representing more than 3 million participants. 

The bottom line of their work, which included meta‐analysis, systematic review, and spline analysis of the cohort studies reviewed, is a definite hormetic relationship, a bell curve between duration and quality of sleep and cardiovascular disease incidence and mortality.

A Matter of Time

In their review of the data, Kwok, et al. observed no significant increase in incidence of stroke or cardiovascular disease mortality in patients with self‐reported sleep intervals of <7 hours. On the other hand, other adverse effects of insufficient sleep are well documented, including increased levels of leptin and ghrelin, metrics that are associated with increased appetite and caloric intake, reduced energy expenditure, and low-grade inflammation. These are associated with impaired glycemic control and obesity and may have less clear ties with cancer and cardiovascular disease.

Perhaps surprisingly, the adverse effects of getting too much sleep are better defined and more dramatic. Kwok, et al. found that self-reported sleep in excess of 8 hours produced increased risk for stroke and cardiovascular disease mortality proportional to the excess:

• 14% increased risk for 9 hours
• 30% increased risk for 10 hours
• 47% increased risk for 11 hours

The moderate risk of cardiovascular harm and mortality increased in direct proportion to the divergence from the recommended durations of sleep. Additionally, as in the case of insufficient sleep, sleep in excess of 8 hours was also associated with non-cardiovascular negative outcomes, including depression, low physical activity, low socioeconomic status, and unemployment.

Quality Matters

Coming as no surprise, the quality of sleep is significant in its association with cardiovascular disease. Abnormal or poor sleep serves as a marker of elevated cardiovascular risk. Non-restorative or unrefreshing sleep increases the risk of coronary heart disease by 47% with a 95% confidence interval, though it should be noted that other outcomes were not observed. Other adverse effects include perpetual tiredness and decreased productivity.