Energy expenditure during sleep, sleep deprivation and sleep following sleep deprivation in adult humans
One of the proposed functions of sleep is to conserve energy. We determined the amount of energy conserved by sleep in humans, how much more energy is expended when missing a night of sleep, and how much energy is conserved during recovery sleep. Findings support the hypothesis that a function of sleep is to conserve energy in humans. Sleep deprivation increased energy expenditure indicating that maintaining wakefulness under bed-rest conditions is energetically costly. Recovery sleep after sleep deprivation reduced energy use compared to baseline sleep suggesting that human metabolic physiology has the capacity to make adjustments to respond to the energetic cost of sleep deprivation. The finding that sleep deprivation increases energy expenditure should not be interpreted that sleep deprivation is a safe or effective strategy for weight loss as other studies have shown that chronic sleep deprivation is associated with impaired cognition and weight gain.
It is interesting, but I would stress that last sentence: chronic sleep deprivation is associated with impaired cognition and weight gain.
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The findings showed that compared to a typical night of sleep, the amount of energy expended by the subjects during 24 hours of sleep deprivation increased about seven per cent. In contrast, energy expenditure decreased to five per cent during the recovery episode, which included 16 hours of wakefulness (following the sleep deprivation night), then eight hours of recovery sleep.
The study proves there is a direct correlation between the sleep–wake cycle and how the body uses energy. It also demonstrates that sleep deprivation is metabolically costly. 'The function of sleep, especially in humans, is considered one of the most important scientific enigmas,' commented Wright, who hopes the new data will help researchers better understand one piece of the sleep puzzle.
One question arising from the study concerns why humans don't conserve more energy during sleep. 'There are other functions of sleep that are important and cost energy,' explains Wright. 'Some conserved energy may be re-distributed to support vital physiological processes like learning and memory consolidation, immune function, and hormone synthesis and release.'