Tonight, let’s look at what happens once you drift off into slumberland, and dive in a little deeper into why it’s so damaging to your health (and fitness goals) when you don’t get enough shut-eye.
Typically, over the course of a night, your body and brain goes through a series of anywhere from four to seven sleep cycles. If uninterrupted, each cycle takes about 90 to 110 minutes, and consists of several distinct stages:
- Stage 1: This initial stage of light sleep (which occurs only when you go from a conscious state to an unconscious one) lasts about 5 or 10 minutes, during which you drift in and out of sleep. Your muscles relax (except when your whole body twitches and you get that sudden “OH CRAP, I’M FALLING!” sensation -- it's called hypnic myclonia, by the way) and your eye movements slow down. You can be awakened pretty easily during Stage 1 sleep; when that occurs, you usually don’t recognize that you fell asleep at all.
- Stage 2: In this second stage of the sleep cycle, which lasts for a half-hour or so, you’re still in light sleep, but your body temperature drops a bit. Also, your eye movements, respiration, heart rate and brain waves slow considerably – interrupted by just a few occasional bursts of rapid brain waves. Fully half of your total sleep time is spent in Stage 2 sleep, which is also called “spindle sleep” because of the spikes (or spindles) in brain activity. These spindles, incidentally, are critical to the brain’s ability to process information.
- Stage 3: When you enter Stage 3 (some experts separate this into two stages – 3 and 4 – but for our purposes, let’s just lump ‘em together), you’re in deep sleep. Your brain begins producing much slower, high-amplitude “delta” waves. When you’re in deep sleep, there’s basically no eye movement or muscle activity. (This is also the time when some kids experience sleepwalking or bedwetting.) It’s very difficult to be awakened from deep sleep – but if you manage to be roused, you’ll likely feel disoriented and out-of-sorts for a while.
- REM Sleep: Rapid eye movement distinguishes REM sleep from the other stages. But it’s not just your eyes that move faster -- during this period, your heart rate increases, blood pressure rises, and breathing becomes rapid, irregular and shallow. Brain waves during REM sleep increase to levels similar to those during regular waking hours, and most of your dreaming occurs during this stage.
If you’re awakened -- by noise, light, your own snoring, your alarm clock -- and you go back to sleep, you actually start over again at square one: Stage 1 sleep. If this happens within the first few minutes of sleeping, no harm, no foul; after all, your head just hit the pillow a few minutes ago. But if some disturbance awakens you while you’re in Stage 2 sleep or beyond, you’ve just deprived yourself of some valuable Stage 3 and REM sleep.
The same goes for inadequate sleep. Go to sleep too late or wake up too early, and you’re missing out on the full benefits of a full night’s rest -- and exposing your mind and body to a host of risks.
What risks, you ask?
First and foremost, lack of sleep can lead to obesity, diabetes and premature aging.
Research suggests that chronic sleep deprivation “may influence weight through effects on appetite, physical activity, and/or thermoregulation,” and that it's linked to the development of type II diabetes. The link between lack of sleep and insulin resistance is clear:
In laboratory studies of healthy young adults submitted to recurrent partial sleep restriction, marked alterations in glucose metabolism including decreased glucose tolerance and insulin sensitivity have been demonstrated. The neuroendocrine regulation of appetite was also affected as the levels of the anorexigenic hormone leptin were decreased, whereas the levels of the orexigenic factor ghrelin were increased. Importantly, these neuroendocrine abnormalities were correlated with increased hunger and appetite, which may lead to overeating and weight gain. Consistent with these laboratory findings, a growing body of epidemiological evidence supports an association between short sleep duration and the risk for obesity and diabetes.In other words, your metabolism is wrecked and your appetite goes haywire.
This appears to be especially the case if your Stage 3 deep sleep is restricted or interrupted -- even if your total sleep time remains the same. A University of Chicago study concluded that suppression of slow-wave “delta” sleep resulted in significant decreases in insulin sensitivity, which leads to reduced glucose tolerance and increased risk for type II diabetes.
Even a single night of partial sleep deprivation can induce insulin resistance in otherwise healthy individuals.
As Robb Wolf put it:
Sleep deprivation mimics many elements of the aging process. One could make the argument that how you feel when you are sleep deprived is likely how you will feel if you are both diabetic and old (sleep deprivation dramatically impacts insulin sensitivity). Improved sleep time and quality will help you: Lean out, avoid depression, autoimmunity, heart disease... It might even help you be a better athlete.Stephan Guyenet has similar stuff to say:
Besides making us miserable, lack of sleep appears to predispose to obesity and diabetes, and probably sets us up for the Big Sleep down the line. I can't say I'm surprised, given how awful I feel after even one night of six hour sleep. I feel best after 9 hours, and I probably average about 8.5. Does it cut into my free time? Sure. But it's worth it to me, because it allows me to enjoy my day much more.Want more? Sleep deprivation will jack up your cortisol -- the hormone released by your adrenal glands in response to stress. “Even partial acute sleep loss” can negatively “affect the resiliency of the stress response and may accelerate the development of metabolic and cognitive consequences of glucocorticoid excess.” If you accumulate high levels of cortisol overnight, you’re more likely to be insulin resistant during the day, which in turn will derail your body’s efforts to efficiently process glucose. Your diet may be clean, but heightened cortisol levels will negate all your awesome Paleosity. Plus, chronically elevated cortisol levels have been linked with decreases in muscle tissue and bone density, elevated blood pressure, and lowered immunity. Fun!
Wait -- what did you say? Oh, so you’re lean and insulin sensitive and a super-kick-ass athlete and think you can therefore get by with less sleep? Consider this: Studies show that even a “relatively low degree of sleep disturbance” can disturb the natural secretion of human growth hormone (HGH) that occurs while you sleep.
Sleep deprivation also impairs your body’s ability to recover from your crazy metcon beatdowns. According to U.C. San Diego study, lack of sleep results in reduced levels of Interleukin-6 (IL-6) -- a cytokine that triggers an immune response to trauma -- including normal microtraumas from exercise.
Not enough to convince you? Okay -- how about this: Another effect of sleep deprivation is lowered testosterone. That's right: Sleeplessness is not a sign of virility -- it's the exact opposite.
Want to get bigger, stronger and faster? Get enough sleep.
For those of you who care about your noggins, there's even more to consider: Sleep deprivation will rob you of the brain-related benefits of REM sleep, which is essential for processing and managing everything from information and memories to emotions and stress.
Even if you like to pride yourself on being a lunkhead who cares not a whit about your brainpower or emotional well-being, think about this: REM sleep is the period when your brain transfers the muscle movements you learn from your short-term memory into your long-term memory. Your hippocampus downloads information to your neo-cortex so that you can recall -- among other things -- how to perform physical skills. In other words, don’t waste your time trying to perfect your snatch technique if you’re not going to get enough sleep.
Check out this handy infographic for more about the risks of sleep interruption and deprivation:
(Click the image above for the full picture.)
The upshot? Go to bed early. Try to wake up without using your alarm clock, or use an alarm that'll gently rouse you rather than jolting you awake. (Gadget hounds: Try the Lark or Zeo.) Worried you won't wake up in time for your early morning meeting or workout? THEN GO TO BED EARLIER. Make sure you keep your room pitch-black -- no nightlights, no glowing LCD displays on your cell phone, clock, DVD player. Cover 'em up if that's what it takes. Get blackout curtains. The light's bad for you and contributes to you getting fatter. And no, I’m not kidding.
I know I’m guilty of not
So I'm off to bed. Are you?