How sleep boosts your energy

Sleep is essential for the body to recover, repair, and function at its best. Understanding sleep cycles can help you improve your sleep habits and wake up genuinely refreshed.

We tend to think of sleep as simply not being awake. But scientists divide it into two major types: REM (rapid eye movement) or dreaming sleep, and non-REM or quiet sleep. Surprisingly, the two are as different from each other as each is from waking - and both may matter for energy.

Non-REM sleep has three stages: light sleep, deeper sleep, and deep sleep. Sleep specialists believe the last stage - deep or slow-wave sleep - is when the body mainly renews and repairs itself. It appears to play the greatest role in energy, enhancing your ability to make ATP, the body's energy molecule.

During deep sleep, blood flow shifts away from the brain, which cools measurably. At the start of this stage the pituitary gland releases a pulse of growth hormone that stimulates tissue growth and muscle repair. Researchers have also found higher blood levels of substances that activate the immune system during deep sleep, raising the possibility that it helps prepare the body to fight infection.

Someone whose deep sleep is cut short wakes up less refreshed than someone who got enough of it. And when a sleep-deprived person finally sleeps, they pass quickly through the lighter stages into deep sleep and spend a greater share of time there - suggesting deep sleep fills an essential role in optimal functioning.

REM sleep, meanwhile, restores the mind, perhaps partly by clearing out irrelevant information. In one set of studies, students tackled a complex puzzle involving abstract shapes; those who slept well after seeing it solved it far better than those asked to solve it immediately - evidence that the brain processes information overnight.