The science of napping

By Elise Moser

woman_sleeping_at_desk

Photo courtesy of the CDC

Sleep deprivation is a reality for many Americans: a 2013 National Sleep Foundation poll found adults in the United States sleep only 6 hours and 31 minutes at night on average, while the Centers for Disease Control and Prevention recommends 7-8 hours of sleep for adults. Sleep deprivation can lead to a myriad of health problems, including depression, sore muscles, increased risk of diabetes, increased blood pressure and weight gain.

Taking a nap can be a useful tool for people to recharge during the day and make up for lost sleep overnight. But there are strategies for daytime sleep that can help you make the most of your nap.

Why do I feel tired during the day?

You can thank your circadian rhythm for a mid-day drop in energy: everyone has an internal biological clock that dictates when we are sleepiest. For most people, these drops in energy occur between 2-4 a.m. and 1-3 p.m.

How do naps differ from sleep that happens overnight?

“As far as we know, the sleep that happens when we nap is not somehow magically different than the sleep that you take at night,” said Sarah Lust, project coordinator at the Center for Health, Intervention and Prevention at the University of Connecticut. “It’s just that it’s happening at a different time of day.”

Lust studied circadian rhythms during an internship at Brown University. She brought this background into her graduate studies at the University of Missouri, where she studied the effects of alchol on decision making. She continues this research at the University of Connecticut.

“We’re studying alcohol prevention research, and still doing a bit of research on the association between how much sleep people get and their helath decisions.

What makes a good nap?

The best way to nap is to pay attention to timing: the human sleep cycle is made up of five stages that last for 90 minutes on average.

Stage 1 and 2 sleep is characterized as being light. They tend to last for about 20 minutes.

“If you were to try to wake (someone in early stage sleep), they’d tell you they were just resting their eyes,” Lust said. “They wouldn’t even know they were asleep yet.”

Stage 3 and 4 sleep is much deeper, Lust said.

“If someone were to try to wake you, you’d really be conked out,” she said.

The final stage is known as rapid eye movement sleep. This is when most dreaming takes place. REM sleep is not a deep sleep like stage 3 and 4 sleep, Lust said. Waking up during REM sleep would be similar to waking up in stage 1 or 2 sleep.

When napping, Lust said its best to wake up in stage 1 or 2 sleep or after completing a full sleep cycle.

“One of the reasons a longer nap can be tricky is that if you get into stage 3-4 and you wake up, you can be very groggy,” she said. “They call that sleep inertia.”

This is why “power naps” are touted as the best way to doze off during the day: resting for 20 minutes won’t put you past stage 1 or 2 sleep.

Can naps make up for lost sleep?

Yes and no, said Lust.

“(Sleep) is truly like a bank,” she said. “If you think that your personal sleep need is about 8 hours, and you only get about 6 hours throughout the week, maybe on Monday, a 20-minute nap is all your body needs to feel refreshed.”

But by Friday, the body needs longer and longer naps to feel better: sometimes up to a full 90-minute sleep cycle.

Lust said it’s better to get most of your sleep at night, instead of trying to catch up during the day with naps.

“For humans, it’s ideal that we get as much sleep at night as possible,” she said. “Ideally, people would get a full night of sleep and their nap, if they needed one at all, would be only 20 minutes.”

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