The science of a good night’s sleep
Why we sleep. For a long time, sleep was thought of as a passive state, a simple switching-off of the body at the end of the day. Research over recent decades has shown the opposite. While we sleep, the brain is highly active: it consolidates memories, clears out waste products that build up during waking hours, and restores the body’s energy. Far from being wasted time, sleep is when much of the day’s learning is made permanent.
The stages of sleep. A night’s sleep is not uniform. It moves through repeated cycles, each lasting roughly ninety minutes and made up of several stages. These range from light sleep, from which a person is easily woken, to deep sleep, during which the body carries out most of its physical repair. Later in the night comes REM sleep, the stage most associated with vivid dreaming. A healthy adult passes through four or five of these cycles each night.
What gets in the way. Modern life offers many obstacles to good sleep. The blue light from phones and tablets can suppress melatonin, the hormone that signals to the body that it is time to rest, which is why experts advise against screens in the hour before bed. Caffeine, taken too late in the day, can remain in the system for many hours. Irregular hours, such as those worked by night-shift staff, disrupt the body’s internal clock and are among the hardest patterns to adjust to.
The cost of too little. The effects of poor sleep go well beyond feeling tired. In the short term, concentration and mood suffer and reaction times slow, which is why driving while sleep-deprived is so dangerous. Over longer periods, a persistent lack of sleep has been linked to a weakened immune system and to a higher risk of several serious health conditions. Sleep, researchers now argue, is not a luxury but a necessity.
Building better habits. The good news is that sleep can usually be improved without medication. Specialists recommend a consistent routine: going to bed and getting up at the same time each day, even at weekends. A cool, dark and quiet bedroom helps, as does avoiding heavy meals late in the evening. For those who lie awake worrying, keeping a notebook by the bed to jot down concerns can help clear the mind. These simple measures are together known as sleep hygiene.