Sun, Moon, Day, Night: How natural cycles help you sleep.

How alert or sleepy you feel is determined in large part by two different and somewhat opposing systems: the homeostatic system and the circadian rhythm.

The homeostatic system is sleep-promoting. It runs on a simple, linear principle: the longer you have been awake, the more you want to sleep.

You have probably heard of the circadian rhythm. The circadian rhythm is our internal biological clock, and it is influenced by the sun, or daylight. The circadian rhythm is wake-promoting; the more time you have been exposed to daylight, the more awake you feel. Incidentally, the circadian rhythm influences all kinds of body functions, such as body temperature, blood pressure, and even when we perform best athletically (for most people, athletic ability is best in the late afternoon).

Here is an example of how the circadian rhythm and homeostatic system work in the body. Early in the morning, and especially if you haven’t had enough sleep, you may still feel sleepy. But over the next few hours, you’re accumulating daylight exposure and will start to feel more awake. As the sun goes down, the circadian and homeostatic systems work together to promote sleep: it’s been a long time since you were in bed (homeostatic), and it is dark out (circadian).

When the brain detects darkness, it begins to produce a hormone called melatonin, which makes you feel sleepy. Interestingly, most teens have a delay in their melatonin production, so that they have trouble falling asleep before around 11 pm. (LINK TO BLOG POST Benefits of a good night’s sleep)

Modern life can interfere with this natural process in some profound ways; the clearest example of this is that we light our homes in the evening, and more importantly we use computers, which give off a bluish light. Blue light tricks our brains into thinking we are out in daylight, and interferes with our production of melatonin, the hormone makes us feel sleepy.

So if you are working on an assignment that is due at midnight, it may be hard to fall asleep right after you turn it in.

Now that you understand how sleep works, you might want to check out this list of sleep-hacking suggestions.