Dakota Johnson says she sleeps up to 14 hours per night. Is too much sleep a bad thing?

Is it healthy to sleep 10 to 14 hours per night? Dakota Johnson thinks so.

The "Fifty Shades of Grey" star, 34, shared in an interview with the Wall Street Journal, published Monday, that she's "not functional" if she gets less than 10 hours of sleep and "can easily go 14 hours" asleep in one night.

"I don’t have a regular (wake-up) time," she said. "It depends on what’s happening in my life. If I’m not working, if I have a day off on a Monday, then I will sleep as long as I can. Sleep is my number one priority in life."

Experts say the ideal amount of sleep varies depending on the individual; but, pushing 14 hours is likely overdoing it.

"There’s a range," explains Shelby Harris, a licensed clinical psychologist and the author of "The Women's Guide to Overcoming Insomnia: Get a Good Night's Sleep without Relying on Medication." "The majority of people fall somewhere between seven to nine hours of sleep a night ... but there are some people who are outliers, with some needing only six hours and others closer to 10."

What is sleep hygiene?Tips and changes you can make to get better quality sleep.

How much sleep should you get, according to research?

For middle-aged to olderpeople looking to get the best sleep possible, seven hours of consistent sleep may be the sweet spot, research suggests. The American Academy of Sleep Medicine advises adults get at least seven hours of sleep per night and teens get eight to 10.

More:Seven hours of consistent sleep may be best for middle-aged, older people, researchers say

Is there such a thing as too much sleep?

Though many struggle to get enough sleep, it's also possible to get too much of it.

Harris says what's too much sleep varies for each individual, but more than 10 is likely overboard. This can result in feeling "sleep drunk," or especially groggy or foggy, in the morning, she says.

"Some people can feel fine if they’re naturally longer sleepers, but oftentimes people who are very long sleepers don’t usually feel like the sleep is refreshing," she says.

Oversleeping may also be a red flag of an underlying sleep disorder, such as hypersomnia or sleep apnea, says Sarah Silverman, a licensed psychologist and behavioral sleep medicine specialist.

"Sleep is just like shoe size," she says. "One size does not fit all, and some people are going to need more than eight. Some people are going to need less than eight. But really, I'd say that the sweet spot is going to be the number of hours of sleep that allows you to feel your best."

Joe Biden uses CPAP for sleep apnea:What to know about the common sleep disorder.

Why does getting enough sleep matter?

As people sleep, their brains work to consolidate memories and process things learned during the day, particularly during what's called deep sleep, Barbara Sahakian, a professor in the psychiatry department at the University of Cambridge, previously told USA TODAY.

But too little or too much sleep can create chronic stress. It can also cause changes in the hippocampus, a part of the brain vital to learning and memory, Sahakian said.

How can you improve your sleep?

If you’re looking to improve your nighttime habits and feel well-rested, here are some tips to better your sleep hygiene:

• Stay consistent: A regular bed and wake-up time can help set your biological clock to become sleepy at the same time every day.
• Wind down: A period of “wind-down time” is another step to ensure you’re getting a good quality night of sleep. Try a relaxing meditation, a warm bath or shower, reading, or listening to calming music
• Establish your sleeping space: The bedroom should be a cool, dark, quiet and comfortable place to ensure the best possible sleep experience. Dark shades and earplugs can help achieve this.
• Avoid alcohol, food, caffeine and electronics before bed: Eating before bed has been known to cause acid reflux, and caffeinated beverages (including soda, coffee, tea and chocolate) may keep you up at night. And while you may be tempted to end the night with a glass of wine, alcohol can impact your sleep. You should also avoid using electronics before bed and even leave them outside of the bedroom.
• Exercise regularly: Several studies have linked increased aerobic exercise and better quality sleep for individuals with insomnia.

Contributing: Saleen Martin, Daryl Austin and Clare Mulroy