Too Much Sleep Could Increase Risk of Death and Coronary Heart Disease, Study Says

The American Academy of Sleep Medicine and the Sleep Research Society officially recommend adults sleep at least seven to nine hours per night but offer no formal caution against sleeping more than that amount. A new study, however, suggests that sleeping too much could do more harm than sleeping too little.

Sleeping more than seven to eight hours a night may increase the risk of death from heart disease or stroke, while clocking fewer than seven hours did not affect one's likelihood of death, researchers found in an August study published in the Journal of the American Heart Association. Their results indicate sleep quality and consistency as a critical risk factor for cardiovascular disease.

In an analysis of 74 studies of more than 3.3 million participants that examined the link between sleep duration and cardiovascular disease, researchers concluded that participants who slept for 10 hours were 30 percent more likely to die and nearly 50 percent more likely to develop cardiovascular disease.

Excessive sleep is often a symptom of latent diseases that precedes a formal diagnosis of conditions like heart disease and obstructive sleep apnea, a potentially dangerous condition in which breathing abruptly stops and starts, lead author Chin Shing Kwok said. Other conditions, like chronic inflammatory disorders and depression, can cause fatigue and impact sleep patterns.

Still, not sleeping enough can indirectly influence mortality: Fewer hours of sleep can increase levels of leptin, the hormone that accelerates appetite and the amount of calories consumed per day, which significantly raises one's risk of obesity. One in three Americans sleeps less than seven hours per night regularly, the Centers for Disease Control and Prevention reported, which might explain why two in three adults in the U.S. are considered overweight or obese.

too much sleep causes death heart disease
A man tries out a high-tech bed at a January 2014 trade show in Las Vegas. Researchers warn that sleeping more than the recommended seven to eight hours a night could significantly increase one's risk of death and heart disease, while sleeping fewer than seven hours did not significantly impact mortality. (Photo by Justin Sullivan/Getty Images)

Inadequate sleep has also been found to elevate blood pressure, said Sheldon Sheps, former chair of the Division of Nephrology and Hypertension at Mayo Clinic. Sleep regulates stress hormones and maintains healthy nervous system functioning, and too little of it can damage the body's ability to regulate stress, resulting in high blood pressure.

While sleeping more than eight hours on occasion won't significantly impact health, consistency is key. Participants with irregular sleep patterns were nearly 45 percent more likely to develop coronary heart disease, researchers found. Past studies have showed that interrupting one's Circadian rhythm, or the body's internal 24-hour clock, can dull cognitive abilities and cause erratic emotional shifts. Common environmental and social disruptors, like artificial lighting, demanding works schedules and family care duties, create a vicious cycle of insufficient sleep followed by too much to compensate.

"Sleep is not like a bank," sleep scientist Matthew Walker told NPR in 2017. "You can't accumulate a debt and pay it off at a later point in time. If I were to deprive you of sleep an entire night, and then in a subsequent night give you all the sleep you want, you never get back all that you've lost."

Though the study's authors cautioned against excessive snoozing, others suggest that catching up on lost sleep over the weekend could bolster health: In May, researchers posited that logging nine hours on Saturday after only sleeping five hours a night throughout the week reversed participants' heightened risk of mortality.