You might not need 8 hours of rest. Here’s how to find your perfect sleep time

By Gina Park, CNN

(CNN) — With so much to do heading into the busy holiday season, is anyone getting enough sleep?

Most sleep experts advise that adults get seven to nine hours of sleep per night for good health and emotional well-being (although that changes as you get older). And studies warn that sleeping for less than seven hours a day can increase the risk of obesity, high blood pressure, heart disease and other issues that come with sleep deprivation.

CNN has reported on those risks, too, including how getting five hours or less of sleep can increase the likelihood of developing chronic disease.

Dr. Tony Cunningham, clinical psychologist and director of the Center for Sleep and Cognition in Boston, said it isn’t as simple as getting the “right” number of hours of sleep. In a conversation with CNN, he explained his thinking.

Sleep quality is just as important as sleep time

A lot of people tend to focus on how many hours of sleep they’re getting but neglect the quality of their sleep, which can be even more important than sleep time.

“There’s two different things going on in our bodies that dictate both the type of sleep that we’re getting and the quality of sleep that we’re getting, and that is our sleep pressure and circadian rhythms,” said Cunningham, who is also an assistant professor of psychology at Harvard Medical School.

Sleep pressure or sleep drive builds up the longer that you’re awake and decreases while you’re asleep. It’s what causes you to start feeling tired after being awake for an extended period.

“It’s just like eating,” Cunningham said. “The longer it’s been since you’ve eaten, the hungrier you get.”

To get a good night’s worth of sleep, you want to get into bed when you’ve built up a lot of sleep pressure.

Your circadian rhythm is your body’s internal clock.

Don’t let the name fool you though. Although external factors, such as light, can affect your circadian rhythm, the pattern that your body follows is guided by your brain.

“The circadian rhythm can fluctuate and send either sleep-promoting signals or wake-promoting signals throughout the course of the day,” Cunningham said. “So, if you’ve ever pulled an all-nighter and you’ve gotten a second wind in the middle of the night, and you felt less tired, then that is your circadian rhythm kicking in.”

For higher sleep quality, sleep pressure and your circadian rhythm should be working together. That means that any abrupt changes or an irregular sleep schedule can affect your ability to sleep and lower sleep quality.

One way to enhance sleep quality “is to start waking up at the same time every day, as it can be a little bit more impactful than going to bed at the same time every day — because it’s not always a good idea to go to bed if you’re not sleepy yet,” Cunningham said.

Once you have a general sleep schedule or routine, then your body will naturally start to seek out its optimal sleep time.

How many hours of sleep do you need?

There is nothing wrong about advising people to get an average of seven to nine hours of sleep, but it’s important to remember that this range is the average.

“That does not mean that every single person on the planet needs eight hours of sleep,” Cunningham said. “There are some people that really, truly only need five or six hours — like their biology and physiology only would allow them at optimal functioning to get five to six hours of sleep.”

This goes both ways though. “There are also people out there that need nine, 10, 11 hours of sleep per night,” he added.

To figure out how much sleep you need, you can do these two things.

“You’re going to keep a consistent bedtime. I want it to be a bedtime that you are pretty confident you’ll be able to fall asleep within no more than 20 to 30 minutes,” Cunningham said.

Your bedtime should be when you’re feeling sleepy, not just tired. If you get into bed and can’t fall asleep within that 20-to-30-minute range, then it’s likely that you haven’t built up enough sleep pressure.

If that’s the case, it’s better to engage in some low-arousing activities, such as taking a bath or meditating with the lights dimmed, until you start to feel sleepy.

“Then you need to find a period of time in your life where you can sleep until you wake up naturally with no alarm,” Cunningham said.

“Go around your room, hide your clocks, block out the curtains, maybe do noise machines, have an eye mask on. Everything you can do so that you can be in your room, you have no sense of what time it is, and then you go to sleep, and you sleep until you wake up,” he added.

Of course, not everyone has the schedule to do this exercise. But if you’re a student who is home for the holidays or you’ve taken some time off work, it might be a worthwhile experiment, especially if you’re concerned about the amount of sleep you’re getting.

“The first couple of days, you’re probably going to sleep for longer than you normally would,” he said. “So, if you let yourself go to bed at midnight, it’s not uncommon for people to sleep until like 10 or 11 in the morning the first couple of days, while they catch up on their sleep pressure.”

After those first few days of catching up, you’ll know you’ve found your sleep time “when you wake up for three or four days in a row at approximately the same time with no external cues, no light cues and no alarm,” he said.

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