Just What is Healthy Sleep?

Reader’s Question

I’m 20 years old and I’ve probably averaged about 6 hours of sleep a night since adolescence. There have been nights when I might get 8-10 hours, but they are very rare. For as long as I can remember, I’ve always been fairly tired during the day. That being said, when I lie down to sleep I do not fall asleep quickly. From what I’ve read, if you have a significant amount of sleep debt, you should fall asleep in the first few minutes.

Also, my body seems to naturally want to be awake at night — I’m not tired and I focus better. During the day I am tired, but around 8:00-9:00 pm I’ll be wide awake. Some nights I’ll be up reading until 5:00 am, and not realize it until the sun starts to rise.

Normally, I wake up at 8:00 am without an alarm or any real reason to wake up. I do not have any early classes, nor do I have a job for most of the year.

So I’m really not sure what my body wants and, more importantly, what it needs. I’m earning good grades, so my brain is not completely worthless as far as attention and learning goes. But if a sleep debt is preventing me from operating at 100%, I certainly would like to rid myself of it. I probably won’t have time to do so during the school year, but I will definitely try to get 10 hours of sleep a night to balance out my sleep debt if it will help.

Should I be getting more sleep? For how long can a sleep debt accumulate? How can I fall asleep earlier? Why am I tired during the day, but wide awake at night?

Psychologist’s Reply

It seems that so many of us have heard about the magical number — 8 hours — we’re supposed to sleep for good health. In reality, people vary (sometimes quite widely) in the amount of sleep needed. Fortunately, if we absolutely need more sleep, our bodies will make sure we get it. In extreme situations in which a person is very sleep deprived but must remain awake for personal safety, such individuals have been known to experience repeated microsleep episodes, lasting only a few seconds at a time.

You make reference to a sleep debt, but even that concept has more to do with the type or stage of sleep than the absolute time spent sleeping. The stage of sleep we seem to need most is rapid eye movement (REM) sleep. Researchers have documented what they refer to as the REM rebound effect: when deprived of REM sleep, we get into the REM cycle more quickly, and stay in it longer, the next time we sleep. So, if sleep deprived one night, the following night is liable to involve more REM sleep, even if the total number of hours of sleep is typical for us.

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Then there is the importance of our personal circadian (daily) rhythms. Yes, we all follow the same daily cycle comprised of precisely 24 hours, simply because we all use the same system of time to regulate human activity. However, our body doesn’t necessarily follow a precisely 24-hour day, and there is individual variation in the length of the daily cycle (although it is close to 24 hours for humans). Our pineal gland, a small round gland in the center of our brain, is responsible for keeping our bodies in sync with the day/night cycle. It does so by releasing melatonin to make us drowsy and ready to fall asleep. Melatonin is released on a rhythmic schedule, but its release is also sensitive to light. Bright light suppresses release of melatonin, whereas darkness facilitates it.

This connection between melatonin and darkness seems adaptive when considering our evolutionary history. Human night vision is not as good as that of some predators, so we would have been safest sleeping during the dark hours, rather than awake and active. In modern environments, however, we have artificial light, and the portion of the light spectrum used to illuminate our electronic devices is especially effective at suppressing release of melatonin. As a result, we may be suppressing our natural sleep by staring into electronic screens right up until what was supposed to be bedtime.

Although humans generally sleep at night and are active during the day, there is individual variation in when the “day” starts. Some people tend to naturally function best mentally and physically in the evening and tend to stay up later. Others truly are “morning people” and function best earlier in the day (and tend to go to bed earlier). Certainly we can make ourselves follow whatever schedule is dictated, but here we’re talking about how each individual seems to function based on his or her biological temperament. And last, there is controversy over whether humans function best by obtaining all of their sleep in one dose or by having one or more naps during the day (and perhaps that too varies across individuals).

I imagine that you can see that there are multiple possible answers to your questions. After becoming more aware of how you may be tampering with your natural cycle by your habits and use of bright lights, my advice is simply to listen to your body as to what kind of sleep schedule feels natural. Recognizing that, when it comes to sleep and circadian rhythms, one size doesn’t fit all, allows us to worry less about whether we’re somehow “doing it wrong.”