If you’ve ever awakened from a nice nap and returned to a difficult problem with an easy solution, you have experienced the improved brain function that can result from deep sleep. A good nap can wash away brain plaques that cause foggy thinking, according to scientific studies1. As our brains conduct the daily business of scheduling, decision-making, and other cerebral tasks, our neural cells give off a sticky by-product called beta-amyloid2. This corrosive goo eats away at our brain’s neural network if it’s not cleaned out regularly. If it builds up over time, it can cause dementia.3

When we sleep, the interstitial space among our brain’s neural cells and capillaries4 increases by 60 percent to allow for a rush of cleansing cerebral-spinal and interstitial fluids.5 These rivulets of fluid wash away the beta-amyloid plaques that are the key culprit in Alzheimer’s. The very reason we sleep is to allow this cleansing process. [Researchers are still speculating on the purpose of REM sleep, which only happens while the sleeper is dreaming.]

A nap that lasts 30 – 90 minutes can sharpen your cognitive skills. Sleep is divided into two types – REM (rapid eye movement) sleep and non-REM sleep. Non-REM sleep comes in three stages known as N1, N2, and N3.7 Stage one is the threshold of sleep wherein the sleeper feels relaxed and drowsy, but can still hear surrounding noises. This stage usually lasts five to ten minutes. You can easily wake up stage one sleepers.8 Stage two is a slow descent into deep sleep and lasts 10 to 25 minutes.9 During stage three, also known as deep sleep, the brain’s interstitial space opens up for the deep cleanse.

In a study cited by Johns Hopkins School of Medicine, adults who napped for 30 – 90 minutes had better word recall and were better at figure drawing than a control group who didn’t nap. Better word recall and more accurate figure drawing are both signs of improved brain function.10

Napping longer than 90 minutes can impair your ability to think and form memories and should be avoided.6 It takes your brain 90 minutes to go into a stage of sleep known as REM (rapid eye movement). If you trigger the REM cycle, and then break it when you wake up, you could wind up feeling foggy for the rest of the day. Napping too long can also interfere with your normal night-time sleep cycles.

But a shorter nap can still refresh your brain and bestow better cognitive function than no nap at all. The ideal time of day to take a nap is between 1 to 3 p.m. so you can wake up by 4 p.m. This allows roughly six hours of wakeful activity to prepare your brain for a good night’s sleep. 

Additional benefits from napping include sleeping deeper and longer through the night, improved mood, healthier weight, and, thanks to the cell repair that occurs during deep sleep, a better complexion.

1 Lulu Xie, et al.

Sleep drives metabolite clearance from the adult brain (2013)

National Institutes of Health

https://pubmed.ncbi.nlm.nih.gov/24136970/

“…we show that natural sleep or anesthesia are associated with a 60% increase in the interstitial space, resulting in a striking increase in convective exchange of cerebrospinal fluid with interstitial fluid. In turn, convective fluxes of interstitial fluid increased the rate of β-amyloid clearance during sleep.”

2 Beta-amyloids and the amyloid hypothesis

Alzheimer’s Association

https://www.alz.org/national/documents/topicsheet_betaamyloid.pdf

“One prime suspect is a microscopic brain protein fragment called beta-amyloid, a sticky compound that accumulates in the brain, disrupting communication between brain cells and eventually killing them. Some researchers believe that flaws in the processes governing production, accumulation or disposal of beta-amyloid are the primary cause of Alzheimer’s.”

3 Ibid.

4 Yiming Lei, et al.

The brain interstitial system: Anatomy, modeling, in vivo measurement, and applications (2015)

Science Direct

https://www.sciencedirect.com/science/article/pii/S0301008215300691

“Thus, it is also important to consider the influence of brain interstitial system (ISS), which refers to the space among neural cells and capillaries.”

5 Lulu Xie, et al.

Sleep drives metabolite clearance from the adult brain (2013)

National Institutes of Health

https://pubmed.ncbi.nlm.nih.gov/24136970/

“…we show that natural sleep or anesthesia are associated with a 60% increase in the interstitial space, resulting in a striking increase in convective exchange of cerebrospinal fluid with interstitial fluid. In turn, convective fluxes of interstitial fluid increased the rate of β-amyloid clearance during sleep.”

6 Can a Nap Boost Brain Health?

Johns Hopkins Medicine

https://www.hopkinsmedicine.org/health/wellness-and-prevention/can-a-nap-boost-brain-health

“While a 30- to 90-minute nap in older adults appears to have brain benefits, anything longer than an hour and a half may create problems with cognition, the ability to think and form memories…”

7 Cari Nierenberg

REM vs. Non-REM Sleep: The Stages of Sleep (2017)

Live Science

https://www.livescience.com/59872-stages-of-sleep.html

“This is a relatively light form of sleep that lasts about 5 to 10 minutes.”

8 Ibid.

“A person can be easily awakened from N1 sleep…”

9 Ibid.

“Shortly after N1 sleep ends, a person enters this second stage of non-REM sleep, which typically lasts 10 to 25 minutes…”

10 Can a Nap Boost Brain Health?

Johns Hopkins Medicine

https://www.hopkinsmedicine.org/health/wellness-and-prevention/can-a-nap-boost-brain-health

“Scientists found that people who napped for 30 to 90 minutes had better word recall – which is a sign of good memory – than people who did not nap or who napped for longer than 90 minutes. People who napped for that golden 30 to 90 minutes were also better at figure drawing, another sign of good cognition.”