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By Meghan Holohan

We know sleep is important. But most of us understand little about it, clinging to myths. Sometimes there is a nugget of truth in the misperceptions. But when we're wrong, the result can be exhausting, wakeful nights.

Watch our video with TODAY anchor Al Roker busting some stubborn sleep myths:

These are six of the most common myths: 

1. Naps make it harder to sleep at night

Actually, a short daytime nap can restore your brain power and performance

“If you are really failing during the day … take a nap,” says Winter. “It’s amazing how good that short little nap will make you feel and that makes a difference in how [you] sleep.”

Napping for 15 to 30 minutes can refresh people, allowing them to continue with their day and help people snooze better at night. But make sure that nap is short and sweet. A two-hour nap, for example, will definitely make it tough to sleep later.

2. We need eight hours of sleep a night

Doctors frequently recommend that people get eight hours of sleep to feel their best. Try seven.

“Seven and a half is probably a good average,” says Winter. “It’s a unique number. You need as much [sleep] as you need.”

Recent research even found that people who sleep between 6.5 and 7.4 hours a night live longer than those who sleep for 8 hours or more.

We need to let go of “the idea that people need to get eight hours of sleep,” Winter says.

3. No eating after 8 p.m.

That popcorn at 9 p.m. won’t stop the Sandman from visiting. Eating later at night doesn’t always lead to bad sleep.

“It probably relates more to what you are eating. Desserts, caffeine, sugar are probably destructive. If you think about Thanksgiving … that big carbohydrate meal is sleep promoting,” says Winter.

In fact, a recent study showed that when mice received the right amount of insulin it sparked drowsiness. The results indicate that eating carbs might reset a person’s circadian clock, the mechanism responsible for telling our bodies when to wake and when to sleep.

While noshing at night is okay, people still need to be careful what they eat late at night. Some foods cause indigestion, which might cause people to wake throughout the night.

4. You can bank sleep

Got a big sleep debt? Many try to make up the deficit by sleeping late over the weekend.

“You probably can’t catch up on it,” says Dr. W. Christopher Winter, a sleep medicine expert at Charlottesville Neurology & Sleep Medicine in Virginia.

But there is a caveat. If the busy schedule meant less sleep, but the sleep was restful and efficient, you probably are fine. Resting up before a long night can help, but not if the deprivation is chronic, studies suggest.

Overall, it’s better to nap on sleep-deprived days instead of waiting for the weekend to sleep until noon, says Winter.

Rokerthon: How Al will make it through his 34-hour weathercast

5. The older you are, the less sleep you need

“There is this notion, this myth that older people don’t need as much sleep as younger people,” says Dr. Alon Avidan, director of the UCLA Sleep Disorders Center. “Older adults need as much sleep as a younger person.”

Many older adults struggle to stay asleep, perhaps getting four or five hours of sleep a night. They think they are functioning well and their doctors might even agree that they don’t need as much sleep. But if they needed seven hour of sleep when they were in their 30s, they need seven hours of sleep in their 70s.

Poor sleep could be a sign of another problem, such as sleep apnea, Parkinson’s disease, rheumatoid arthritis, congestive heart disease, or restless legs syndrome, says Avidan. Don't simply accept poor sleep as normal.

6. Exercise cures insomnia

People plagued with insomnia often try anything to fix their sleeping problems. Many believe a good workout will cure their inability to sleep. While working out certainly increases the body’s sleep need, it isn’t the panacea many hope it is.

“I think it would be rare that exercise can cure insomnia,” says Dr. Timothy Morgenthaler, president of the American Academy of Sleep Medicine and a professor at Mayo Clinic. “If what we are talking about is being active for 30 to 60 minutes a day [then] there’s measurable improvement in the quality of sleep.”

Exercise won’t cure the medical reason behind the poor sleep. The bottom line: see a doctor after several days of poor sleep. There might be something else causing your wakeful nights.

All week TODAY's "Snooze or Lose" series explores how America sleeps — or doesn't offering expert-approved ways to get a good night's rest.