It seems we're always being told to get more sleep — and for good reason.
Studies suggest skimping on sleep can lead to obesity, diabetes and even cancer. You might even find yourself with a head-full of false memories.
But rarely does science explore the dark side of sleeping too much. Maybe that's probably because few of us in today's work-addled world have the luxury of exploring that option.
It turns out, even that end of the sleep spectrum is not without its perils.
In a new study published in the journal Neurology, researchers plumbed the sleep patterns of those "fortunate" few — and found they may not be so lucky after all.
In fact, they found that people who take long naps or who sleep nine or more hours at night may have a greater risk of stroke than those who get less sleep.
Specifically, researchers discovered that people who get nine or more hours of sleep are 23% more likely to later have a stroke than people who sleep between seven and eight hours each night. People who take regular naps lasting more than 90 minutes were 25% more likely to eventually have a stroke than people who nap less than 30 minutes.
Scientists say more research is needed to understand how all this sleeping is tied to stroke risk, but point out that earlier findings show that people who sleep a lot often have cholesterol issues and other risk factors for stroke.
"In addition, long napping and sleeping may suggest an overall inactive lifestyle, which is also related to increased risk of stroke," study author Xiaomin Zhang, M.D., Ph.D., of Huazhong University of Science and Technology in Wuhan, China, said in a statement.
Sleep, your heart and your life span
In a similar study published in the Journal of the American Heart Association, researchers found people who get more than eight hours of sleep have greater mortality and cardiovascular risk compared to those who cobbled together less than seven hours.
What's more, sleep-aholics — those who manage to get 10 hours a night — stood a 30% higher chance of dying compared to the seven-hour crowd.
"Our study has an important public health impact in that it shows that excessive sleep is a marker of elevated cardiovascular risk," lead researcher Chun Shing Kwok of Keele University notes in a press release.
The wide-ranging global study involved more than 3 million people who self-reported on their sleep habits — and came to an eye-opening conclusion:
If you tend to sleep a lot, you may want to invest in an alarm clock. Or even a rooster.
Because, as with all things in life, sleep is best taken in moderation.
What about sleeping in on the weekends?
You may be thinking: Well what if I only sleep in on Saturday and Sunday, am I still at risk? The answer is yes, according to a 2019 study published in Current Biology .
Researchers discovered that even if a person sleeps more than seven hours on the weekends but still sleeps less than that on weeknights, they are at risk of gaining weight and developing a sensitivity to insulin.
For the study, 36 participants were divided into three groups that each had a different sleep schedule: nine hours every night, five hours every night and five hours Monday-Friday and sleeping in on the weekends. Both sleep-deprived groups consumed more food and gained weight. Researchers noted that hunger hormones are triggered by lack of sleep.
"One of the things we and others have found in the past is that when people don't sleep enough, they tend to eat more, partly because their body is burning more calories," study author Kenneth Wright Jr., sleep lab director at the University of Colorado in Boulder, told CNN. "But what happens is that people eat more than they need and therefore gain weight."
The group that slept in on the weekends also showed signs of increased insulin sensitivity.
"That helps us understand why is it that when we don't get enough sleep, we have an increased risk for things like diabetes," said Wright, because "short, insufficient sleep schedules will lead to an inability to regulate blood sugar and increases the risk of metabolic disease in the long term."
Symptoms of metabolic disease include high blood pressure, high blood sugar, change in cholesterol and weight gain and increases the risk of heart disease, diabetes and stroke.
Of course, this raises a chicken-or-the-egg question: Do people with high mortality rates tend to sleep more? Or do people who sleep more tend to develop higher mortality rates because of it?
Sleep, the final doctor/patient frontier
In any case, the research points to a new and possibly life-saving line of questioning at the doctor's office: Namely, how much do you sleep?
"The important message is that abnormal sleep is a marker of elevated cardiovascular risk and greater consideration should be given in exploring both duration and sleep quality during patient consultations," Kwok says.
The sweet spot for sleep? That time-tested prescription of seven to eight hours.
The researchers admit that sleep is a many-splintered thing — and the amount we can scrape together on any given day fluctuates wildly. It isn't like a multivitamin that we can pop daily and be assured of healthful results.
"The amount and quality of our sleep is complex," Kwok explains. "There are cultural, social, psychological, behavioral, pathophysiological and environmental influences on our sleep such as the need to care for children or family members, irregular working shift patterns, physical or mental illness, and the 24-hour availability of commodities in modern society."
We are indeed living in an increasingly time micro-managed society.
And the boss needed that report — and yes, even this story — yesterday.
Editor's note: This article has been updated with new information since it was originally published in August 2018.