Original Link: http://www.boston.com/bostonglobe/ideas/naps/
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For years, naps have gotten a bad rap, derided as a sign of laziness, weakness, or senility. We are "caught" napping or "found asleep at the switch."
But lately napping has garnered new respect, thanks to solid scientific evidence that midday dozing benefits both mental acuity and overall health. A slew of new studies have shown that naps boost alertness, creativity, mood, and productivity in the later hours of the day.
A nap of 60 minutes improves alertness for up to 10 hours. Research on pilots shows that a 26-minute "NASA" nap in flight (while the plane is manned by a copilot) enhanced performance by 34 percent and overall alertness by 54 percent. One Harvard study published this year showed that a 45-minute nap improves learning and memory.
The body benefits, too. Napping reduces stress and lowers the risk of heart attack and stroke, diabetes, and excessive weight gain. Naps make you smarter, healthier, safer. But to understand how you can nap best - when, for how long, to what end - you need to understand your body.
BORN TO NAP
Most mammals sleep for short periods throughout the day. We have consolidated sleep into one long period, but the biological vestige remains. Our bodies are programmed for two periods of intense sleepiness: in the early morning, from about 2 to 4 am, and in the afternoon, between 1 and 3 p.m. This midday wave of drowsiness is not due to heat or too many fries at lunch (it occurs even if we skip eating). Rather, it arises from an afternoon quiescent phase in our physiology, which diminishes our reaction time, memory, coordination, mood, and alertness.
ARE YOU A LARK OR AN OWL?
To determine the best time to nap, it helps to know your "chronotype." What time you would get up and go to sleep if you were entirely free to plan your day? If you're a lark, apt to wake as early as 6 a.m. and go to sleep around 9 or 10 p.m., you're going to feel your nap need around lor 1:30 p.m. If you're an owl, preferring to go to bed alter midnight or 1 a.m., and to wake around 8 or 9 a.m., your afternoon "sleep gate" will open later, closer to 2:30 or 3 pm.
WHAT'S IN A NAP?
In designing the optimal nap you need to grasp its potential components. During sleep, your brain's electrical activity goes through a five-phase cycle:
Stage 1: Falling asleep
Stage 2: Light sleep
Stages 3 and 4: Deep, slow-wave sleep
REM: Dreaming Sleep
A whole cycle lasts about an hour and a half (and repeats during night time sleep)
A short afternoon catnap of 20 minutes yields mostly Stage 2 sleep, which enhances alertness and concentration, elevates mood, and sharpens motor skills. To boost alertness on waking, you can drink a cup of coffee before you nap. Caffeine requires 20 or 30 minutes to take effect, so it will kick in just as you're waking. Naps of up to 45 minutes may also include rapid eye movement (REM) sleep, which enhances creative thinking and boosts sensory processing.
Limit your nap to 45 minutes or less, if you need to spring into action after dozing. Otherwise, you may drift into slow-wave sleep. Waking from this stage results in serious sleep inertia, that feeling of grogginess and disorientation that can last for a half hour or more.
But you might want to take a long nap, at least 90 minutes. Many of us get about an hour to an hour and a half less sleep per night than we need. A new study shows that the sleep-deprived brain toggles between normal activity and complete lapses, or failures, a dangerous state of slowed responses and foggy inattention. Sound familiar?
Naps of 90 to 120 minutes usually comprise all stages, including REM and deep slow-wave sleep, which helps to clear your mind, improve memory recall, and recoup lost sleep. Longer naps in the morning yield more REM steep, while those in the afternoon offer more slow-wave sleep. A nap that is long enough to include a full sleep cycle, at least 90 minutes, will limit sleep inertia by allowing you to wake from REM sleep.
