The long-help belief that energy is conserved during sleep, and that sleep deprivation costs people energy was tested in a study. The energy expenditure in daytime and nighttime was calculated during sleep in a sleep deprived-state and also during recovery sleep. The energy outflow was increased during the sleep-deprived state and was regained to some extent during recovered sleep. No sleep at night meant more energy expenditure, recovered slightly by adjusted sleep. “The 7 percent increase in 24 hour energy expenditure on the sleep deprivation day was nearly offset by the energy saved during the recovery day.”
Lower sleep metabolic rates demonstrate the critical role of sleep in energy conservation. The energy expenditure value has been found to be less while asleep, implying that sleep deprivation leads to an increase in daily total energy expenditure. The present study attempts to estimate exactly the energy conserved during sleep; in other words, energy loss due to missing one night’s sleep. Additionally, energy saved during recovery sleep is believed to compensate for the mentioned energy loss. Among the sleep stages, deep slow-wave sleep is associated with the slightest energy expenditure; with the value on recovery night being least versus regular sleep. Overall metabolism was studied in further analysis.
* One week before the study began, the participants were asked to keep a regulated diet and consistent eight hours of sleep per night.
* The study regimen consisted of eight hours of sleep, a planned 16 hours of wakefulness, eight hours of sleep again, followed by a 40 hour sleep denial and eight hour recovery sleep, while maintaining constant meal content and timing throughout.
* Statistical analysis was based on oxygen utilization, respiratory quotient, protein oxidation, polysomnographic recordings and mean energy expenditure across different stages of sleep.
* The energy spent when a person is awake was definitely higher than while routinely asleep in regular time.
* Sleep deprivation was accompanied by an increase of 32 percent in energy expenditure value and regain of 4 percent with recovery sleep.
* More energy was expended after every daytime meal.
* The wakefulness prior to sleep onset recorded elevated energy expenditure levels among all other sleep states.
This study group was very small. The quantum of energy expenditure linked to the “wakefulness after sleep onset” (WASO) state is often missed. This gives rise to the likelihood of an erroneously calculated energy expenditure value for the brief arousals. The current study was carried out under controlled conditions of participants in bed-rest, while it is highly probable that the routine sleep denial in individuals would be much higher. The study suggests examining whether behavioral, environmental or pathophysiological factors which disrupt sleep, cause higher energy expenditure at night due to increased wakefulness and not due to a higher “sleeping” energy expenditure.
“The total daily energy savings associated with sleep is similar to the energy content of two slices of bread or approximately 225ml of reduced fat 2 percent milk.” The energy lost in one night of sleeplessness is similar to a 68kg adult walking 3 km at a moderate pace. Thus, the assumption that sleep conserves a physiologically significant quantity of energy is substantiated. The metabolic inflow and outflow of energy seems to balance out as a net result of the reduction in energy spent in some metabolic functions, and diverting some of this saved energy to other physiological processes that happen during sleep.
For More Information:
Energy Expenditure during Sleep, Sleep Deprivation and Sleep Following Sleep Deprivation in Adult Humans
The Journal of Physiology, November 2010
By Christopher M. Jung; Edward L. Melanson; University of Colorado, Boulder and the University of Denver-School of Medicine, Aurora, Colorado