Napping is widely believed to be good for you. It's been proven to help alertness, athletic performance, reaction times, and analytical thinking. History is peppered with famous leaders who took strategic power naps, from Napoleon to Churchill. It's not that the sleep of naps is all that different from the one you have nightly; it's just restricted to a "lighter" stage, and that has a lot of implications for the napper's biology, neurochemistry, and general physical health. Napping is good for you, but to understand why, you've got to know what's going on during your 20-minute snooze in the break room.
Sleep isn't just a matter of "deep sleep" and "light sleep". There are, for sleep scientists, three stages: Stage 1, where you're basically skimming the surface and barely feel like you've slept if you're woken from it; Stage 2, when your body begins to rest more completely; and Stage 3, the deepest sleep, which is where dreaming (otherwise known as REM or rapid eye movement sleep). Good naps take place largely in Stage 2. Longer naps risk falling into Stage 3, which is more difficult to rouse from and can cause more grogginess. The optimum nap length, according to the National Institute Of Health, is about 15-20 minutes. It's long enough to get into Stage 2 sleep and reap its recuperative effects, but not long enough to go deeper.
The crucial thing to realize is that it's really hard to sleep for a long time and stop yourself from getting into deeper stages; it's just what our bodies are programmed to do. So a nap is the best way to keep yourself hovering at Stage 2, reaping the benefits, and waking up refreshed and smug when everybody else is suffering the afternoon blues. Here's what happens in those sacred 20 minutes.
1. Expecting A Nap Lowers Your Blood Pressure
This is an intriguing discovery about what bits of a nap are really healthy for you: a study by the American Physiological Society in 2007 found that it's actually in the first stages of a nap, before you've actually fallen asleep, that you encounter its big benefit for your heart: a drop in blood pressure. It seems that simply anticipating a nap makes our heart rate slow and our blood pressure lower, and that we're calmer when we actually enter sleep.
A lot of work has been done on heart health and naps; countries with cultural traditions of siestas are reported to have lower levels of heart disease-related mortality, and a six-year study of 24,000 Greek people found that people who took three naps a week or more had a 37 percent lower chance of dying of a heart problem. But this was the first time anybody ever pinpointed what happens to the heart throughout napping, and it seems that the first period of lying in darkness, expecting sweet dreams, is just as valuable as the actual refreshing snooze.
2. You Become Disconnected From Your Surroundings
Stage 2 sleep, whether you're napping or falling asleep at night, is the period when you seriously begin to disconnect from your surroundings. It's basically your body altering what it does with its sensory input: when you're awake, you're taking in information about scents, sounds, and other stimuli, but as you reach Stage 2, your body stops interrupting your rest with that information and lets you enter a "bubble" of self-contained sleep.
A 1989 study demonstrated this by putting some sleepers through a basic sensory test: They had to press a button every time they heard a noise. When they were awake, obviously, they pressed the button 100 percent of the time, but as they entered Stage 2 sleep, their accuracy fell off to about five percent. They just weren't "hearing" things in the same way.
3. Your Heart Rate Slows
Blood pressure drops before we start to nap, but during naps themselves the heart rate itself begins to fall away too. It's the same reason that we breathe much slower: our metabolisms have far fewer needs during naps, and our body is under less stress, so its various systems calm down to give everything a break.
Interestingly, this heart-rate slowing continues all the way down into deep sleep and REM sleep, which is when we start to dream — and that's when it might kick up again. This is one of the other reasons why short naps that don't allow us time to slip into REM may be a good idea: it gives a more consistent short-term rest to the heart.
4. Your Body Temperature Drops
The body has an internal thermostat called its thermoregulation system. And if you've always found it trickier to sleep in hotter environments, you're not alone: part of the body's sleep procedure during Stage 2 sleep is a lowering in overall body temperature. Part of this is that the body is using less energy and doesn't need internal heat; like most mammals, our thermoregulation system is fine-tuned to send us to Stage 2 sleep when our body temperature is dropping the fastest.
This is why it's generally not recommended to try and nap after a hot bath or heated exercise: it won't come to you as easily, and you'll take a long time to settle down, as your body is poised at its wakeful temperature.
5. Your Brain Waves Slow Down
The particular actions of your brain during Stage 2 sleep are actually some of the most interesting it'll ever do. Even if you think you're lying there like a vegetable, your brain is producing some unique wave patterns. Stage 2 sleep is characterized by what's called theta waves in the brain, which are slow waves between four and seven hertz, accompanied by some pretty aggressive "jumps" or spikes in activity.
Scientists think that this combination of slow waves and quick bursts is designed to help us suppress our reactions to outside stimuli and help us get into a sleep bubble. They may also be involved in our brain's processing: it seems to be one of the key times when we transfer the day's memories into deeper longterm memory banks.
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