Regularly spending more than eight or nine hours in bed may be a sign of medical issues. (Alamy)

We get it: Sleep is good for us. The National Sleep Foundation regularly campaigns “to celebrate the health benefits of sleep,” and experts have been boosting sleep’s values as no less important than proper diet and exercise.

Insufficient sleep has been linked to stroke, obesity and heart disease. But sleeping too much may also be risky: It, too, is associated with a higher risk of heart disease and obesity, not to mention diabetes and depression.

So, how much is too much? And if you’re sleep-deprived during the week, does sleeping 10 or 11 hours on Saturday and Sunday to catch up put you in any jeopardy?

Most experts say that a healthy amount of sleep for an adult is a regular seven to nine hours a night. And the operative term here is “regular,” meaning the issue isn’t the college kid who power-sleeps 15 hours on vacation to catch up from too much studying (or partying).

When scientists refer to “long sleepers,” they’re referring to people who consistently sleep nine or more hours a night, says Kristen Knutson, a biomedical anthropologist who focuses on sleep research at the University of Chicago’s Department of Medicine.

“Some people just need more than the average amount of sleep to funtion well the next day,” says Alon Y. Avidan, a UCLA neurologist. (Bigstock)

“If you’ve been pulling all-nighters, by all means extend your sleep on the weekend if you can; try to catch up,” Knutson says, “but if you’re sleeping nine or 10 hours night after night after night for months on end . . . then we’ve got to understand why are you sleeping so much.” You might be getting poor-quality sleep, she adds, or are “already on the pathway to illness and your body is reacting by wanting you to sleep more.”

Studies have shown that spending too much time in bed can be associated with some specific health problems. It can disrupt the body’s circadian rhythms, leaving you more prone to illness, for example, and depriving you of sunlight exposure, which can compromise your immune system. One study found elevated levels of C-reactive protein — a systemic marker of chronic low-grade inflammation associated with heart disease — among those who sleep a lot (and those who sleep too little). A study last spring found that those who slept too much were as much at risk of developing diabetes as those who slept too little. Diabetes was least common in people who said they slept seven to nine hours per night.

But experts caution that it can be hard to pinpoint which is the cause and which is the effect when they look at sleep duration and health problems.

In a 2012 study, Rohit Arora, chairman of cardiology at the Chicago Medical School, found that people who slept more than eight hours a night were twice as likely as those who sleep between six and eight hours to have angina — chest pain or discomfort that is often a symptom of heart disease — and also had a slightly higher risk of having coronary artery disease. The caveat, Arora says: “We could not establish a cause-and-effect relationship.”

Neurologist David Rye, whose particular expertise is in excessive daytime sleepiness, says that when a patient expresses concerns about needing too much sleep, he looks for underlying medical problems.Rye, director of Emory University’s Program in Sleep, often checks for hypothyroidism, in which the thyroid doesn’t produce the right balance of hormones.

This condition can influence metabolism and make you need to power-sleep. Some studies suggest that hypothyroidism affects almost 5 percent of U.S. adults. It can be treated fairly easily with drugs.

Another cause of long sleep is obstructive sleep apnea, which is marked by interrupted sleep, snoring and pauses in breathing during sleep, and a drop in oxygen levels. This condition affects as many as 18 million Americans, according to the National Sleep Foundation, and it can leave people fatigued and feeling as if they need more hours in bed. The condition is also associated with obesity — which has many health risks — and is often treated with a C-PAP device, consisting of a mask, a hose and an air pump, which helps improve airflow into the lungs.

One in five U.S. adults shows signs of chronic sleep deprivation

The most common health issue raised by sleeping too much is depression — which people who sleep excessively may not even know they have, says Helene Emsellem, director of the Center for Sleep and Wake Disorders in Chevy Chase. “Sometimes people with extended sleep requirements may have low-grade depression but may not overtly feel unhappiness. They still may have [only] the neurochemical disturbances of depression.” Treating the depression can often lessen the sleep needs — though antidepressants sometimes make people more sleepy.

Not everyone who sleeps nine to 10 hours a day is unhealthy, doctors say. There are the “somewhat rare” folks who happen to be naturally long sleepers, says Alon Y. Avidan, a neurologist who directs the UCLA Sleep Disorders Center. “That’s just a genetic trait: Some people just need more than the average amount of sleep to be functioning well the next day.” He adds that less than 2 percent of people are likely to fall in that category.

Jen Middleton, a mother of two who lives in Northwest Washington, says she is one of them. For as long as she can remember, she has needed nine or 10 hours of sleep a night, much more than other people she knows. Now 40, she says she has been checked for anemia, has no other health issues and feels fine during the day. “My doctor said it’s probably just me, since I’ve had the same sleeping pattern for so long,” she says.

Middleton still sometimes feels self-conscious about it, as though she’s somehow a slacker. “People say, ‘I wish I could do that, but I have so much to do at night,’ ” she says. But it’s just a nonnegotiable part of her schedule.

“What it depends on is: When they wake up, do they feel refreshed?” says Michael Breus, a psychologist in Arizona who specializes in sleep disorders. “If they do after sleeping nine hours, if they can work that into their schedule, I’m not sure I care. But if they’re waking up after nine hours and they don’t feel so hot, there’s something else going on” and it’s worth consulting a doctor.

Ianzito is a freelance journalist in Washington.