Sleep may be natural way of regulating body’s energy consumption
A new analysis posits the theory that the purpose of sleep is to increase the dormant animal’s metabolic efficiency and to minimize risk of predation or other dangers.

The theory proceeds from research conducted by Jerome Siegel, director of the Center for Sleep Research at the Semel Institute for Neuroscience and Human Behavior at UCLA. Siegel and his team studied the sleeping habits of several species to formulate the theory.

Observing the animals showed Siegel that sleep reduces metabolic activity, meaning that it can be used to conserve energy. Animals also hide or burrow in many cases when preparing to sleep, so another aspect of it is to provide security from predation.

The exact relationship between sleep and security varies with age, according to Siegel. "We sleep more deeply when we are young, because we have a high metabolic rate that is greatly reduced during sleep, but also because there are people to protect us," he said. "Our sleep patterns change when we are older, though, because that metabolic rate reduces and we are now the ones doing the alerting and protecting from dangers."

Siegel’s theory helps to explain why lack of sleep can cause a sense of fatigue: a higher metabolic rate throughout the night means more energy was spent. Serotonin supplements may help regulate sleeping patterns in those who have trouble sleeping.