You can, in fact, have too much of a good thing — even sleep, new research suggests.
People who sleep more than eight hours per night have a significantly higher risk for stroke than those who snooze six to eight hours, according to a study published online Wednesday in the journal Neurology.
In the study, researchers followed approximately 9,600 older adults (average age: 62) for about 10 years. During that period, subjects who reported clocking more than eight hours of shuteye nightly were 46 percent more likely to have a stroke, compared with individuals with more moderate sleep durations. Even when researchers accounted for factors such as high blood pressure and physical activity that may have skewed the findings, long sleepers still had an elevated stroke risk.
Short sleep (less than six hours) was associated with a small hike in stroke risk, but the data wasn’t statistically significant (meaning the results could be due to chance).
“It is worth noting excessive sleep as an early sign of increased stroke risk, particularly among older people,” the study authors write. Previous large research studies in the U.S. and China have found similar associations between sleep duration and stroke.
The new research adds to a large body of evidence that shows both sleeping too little and sleeping too much are associated with poorer health and an increased risk for mortality. And sleeping too much seems to be worse than sleeping too little, the statistics show. Long sleepers have about a 20 to 30 percent increased risk for mortality, according to recent meta-analyses. Among short sleepers, that number is about 10 percent.
All of this raises the question: Can too much sleep hurt your health? Or is it just that people in poor health tend to sleep longer?
Dozens of health problems can encourage people to sleep more, which may partly explain the association between long sleep and stroke or mortality. “It’s hard to think of a health condition that doesn’t increase how much you sleep,” says W. Christopher Winter, MD, owner of Charlottesville Neurology and Sleep Medicine and the medical director of the Martha Jefferson Sleep Medicine Center.
Research shows that depression, cancer treatment, a recent heart attack, and even high cholesterol are all associated with lengthy snooze sessions. (For what it’s worth, short sleep is also linked to numerous health problems, including obesity and diabetes.)
“Generally speaking, when individuals are not healthy, there is a tendency to want to sleep more. It’s the body’s natural response,” Winter tells Yahoo Health. Here’s what typically happens: When you’re ill, you have more inflammatory and immune substances circulating in your system. These body chemicals feed back into brain centers that control sleepiness and wakefulness, Winter explains. “The chemicals are working toward trying to restore health to the individual, but in the meantime they’re feeding back to certain parts of the brain that regulate fatigue.”
Poor sleep quality may also partly explain the connection between long bedtime hours and health problems, Winter says. For example, if you have sleep apnea (a common disorder in which your breathing stops numerous times during the night, making sleep unrefreshing), you might snooze longer to try to make up for interrupted shuteye. (The authors of the recent stroke study write that this may have, in fact, played a role in their findings.)
Might excessive sleep be a cause of poor health as well as a consequence? That’s hard to say. No studies have found any direct evidence, but experts have a few theories. Long sleep duration is linked to inflammation, the stroke study’s authors explain. And inflammation may contribute to cardiovascular problems and, down the line, stroke and an increased risk for early death.
Winter hypothesizes that extended sleep, especially when it’s part of an irregular schedule, might throw off the body’s sleep rhythms. “Sleep is dynamic at night — there are a lot of things going on,” he says. “Many hormones all get set based upon sleep rhythms.” When those rhythms get out of whack, hormones and other body systems aren’t regulated as well, he explains.
Too much sleep can, however, worsen certain health problems, such as depression, Winter adds.
How much sleep should you get?
The National Sleep Foundation released new age-based sleep guidelines in February. The updated recommendations say most adults need between seven and nine hours per night.
In his practice, Winter uses seven hours of sleep as a touchstone. If someone sleeps eight, nine, or 10 hours, he’ll investigate to see if extra doze time is making up for restless sleep. Sometimes the cause of bad sleep is obvious — a new baby at home or moving to a noisy apartment. Other times, a sleep study might be warranted to check for disorders that can cause poor-quality sleep.
Sleep needs vary from person to person, Winter says, and it may take some experimentation to find your sweet spot. If you function well on 5.5 hours, for example, try going to 6.5 and see if you feel any better or worse.
Any change in sleep habits is “a big red flag,” Winter stresses. “Any time there’s been a change in sleeping where you need more, that’s unusual. Usually as life goes on you need less sleep.” Dozing more than you used to could signal depression, a sleep disorder, or another health problem. So if you have any noticeable changes in sleep habits, he advises mentioning it to your doctor.
“There are people out there who are long sleepers who are normal and healthy, so you shouldn’t panic one way or the other,” Winter says. “It’s pretty difficult to sleep more than you need to sleep."