A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Why do we sleep?

November 3, 1989

Dear Cecil:

So why do we have to sleep, anyway? I hate spending almost a third of my life in a coma.

Cecil replies:

Why? It helps you understand what it's like being president. Besides, what else are you going to do at 4 AM? The truth is, researchers don't know why we have to sleep, although they have pots of theories. For example:

(1) Sleep restores. In other words, "sleep either allows or promotes physiological processes which rejuvenate the body and the mind," as one researcher puts it. Studies suggest sleep restores neurons and increases production of brain proteins and certain hormones.

(2) Sleep conserves energy. It takes a lot of energy to keep us warm-blooded critters warm-blooded. Since energy consumption drops during sleep, maybe we doze so we don't have to eat all day long (not that that stops a few people I could name). Supporting this theory is the fact that cold-blooded animals have a much less regular sleep-wake cycle.

(3) Sleep keeps you out of trouble. No kidding. Says here, "according to this theoretical position, prehistoric mankind adapted the pattern of sleeping in caves at night, because it protected humans from species physiologically suited to function well in the dark, such as saber-toothed tigers."

(4) Sleep helps you remember. In other words, it gives the brain a chance to process the day's experiences and file them away in the memory. Thus we remember things learned just before sleep better than things learned earlier.

(5) Sleep helps you forget. Unlearning during sleep prevents the brain from becoming overloaded with knowledge. Not, in my observation, a critical problem for most people, but perhaps sleeping simply works all too well.

Complicating matters is the fact that some people thrive on virtually no sleep. In 1973 British researchers reported on a 70-year-old woman who claimed she slept only an hour a night with no daytime naps. In one 72-hour test, during which she was under constant watch, the woman stayed awake 56 hours, then slept only an hour and a half. Yet she remained alert and in good spirits.

According to one study, short sleepers (six hours or less per night) are well-organized, efficient, ambitious, decisive, and self-confident — in other words, totally obnoxious. This suggests the real function of sleep is to let the short sleepers get the jump on the rest of us. Next time your lids get heavy, therefore, think: the short sleepers are out there, smirking.

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