Siesta - Biological Need For Naps

Biological Need For Naps

Older, pre-teenage children are usually capable of napping, but acquire the ability to nap as teenagers as well.

The timing of sleep in humans depends upon a balance between homeostatic sleep propensity, the need for sleep as a function of the amount of time elapsed since the last adequate sleep episode, and circadian rhythms which determine the ideal timing of a correctly structured and restorative sleep episode. The homeostatic pressure to sleep starts growing upon awakening. The circadian signal for wakefulness starts building in the (late) afternoon. As Harvard professor of sleep medicine Charles A. Czeisler notes, "The circadian system is set up in a beautiful way to override the homeostatic drive for sleep."

Thus, in many people, there is a dip when the drive for sleep has been building for hours and the drive for wakefulness has not yet started. This is, again quoting Czeisler, "a great time for a nap." The drive for wakefulness intensifies through the evening, making it difficult to get to sleep 2–3 hours before one's usual bedtime when the wake maintenance zone ends.

In some individuals, "postprandial dip", a brief drop in blood glucose levels caused by the body's normal insulin response to a heavy meal, may produce drowsiness after the meal that can encourage a nap. However, the appearance of the dip is primarily circadian as it occurs also in the absence of the meal.