In the deepest phases of sleep, the brain waves are slowest. Sleep itself has cycles, in which the brain and body move through phases, marked by varying brain activity. Some animals, including dolphins and whales, sleep unihemispherically - one half of the brain sleeps at a time to allow them to be constantly alert. According to a Boston University database of the sleep characteristics of 133 mammalian species, red kangaroos sleep for just under two hours in a 24-hour period, while armadillos and bats can sleep for nearly 20 hours. Researchers have recently discovered that fossilized plants living more than 250 million years ago - just as dinosaurs were starting to appear - already had circadian rhythms that drove them to fold their leaves at night and reopen them during the day.Īll animals sleep, but it can look widely different depending on the species. Ideally, according to Foster and others, society would find ways to mitigate the problems caused by rigid school and work schedules. This equates to over 173 hours of lost sleep per year. One consequence of this is that teachers are generally more alert in the morning, but their students are more alert in the afternoon.Ī 2016 Rand Corporation report calculated that an employee who works irregular hours, commutes 30 to 60 minutes each way, and faces unrealistic time pressures at work sleeps on average about 28.5 minutes per day less than an employee who has regular working hours, commutes no more than 15 minutes one way, and is not exposed to unrealistic time pressure and other psychosocial risk factors at work.
'Eveningness,' or peak alertness at night, tends to be highest in adolescence. Globally, an estimated one in five workers does regular night shift work, according to a 2020 study by the International Agency for Research on Cancer.Ĭircadian rhythms shift with age. It's been estimated that more than half the population in industrialized societies may have circadian rhythms that are out of sync with their schedules. Other studies suggest we also face higher odds for divorce and road accidents. But when it lasts months or years, we become more vulnerable to cognitive and emotional effects and eventually to cardiovascular diseases, mental illness, diabetes, overweight, and other metabolic disorders, Foster said. It churns out stress hormones, releases hunger hormones, pumps extra sugar into the blood, and raises blood pressure.įor brief periods, this is not harmful. 'Night owls' do best if they can sleep until later in the morning.īut when our routines don't match our biological cycles, the body tries to compensate using responses that evolved to help early humans survive danger, neuroscientist Foster said.
Naturally early risers, or morning 'larks,' do best when they can wake up early and sleep early. People whose lives are synchronized with their body clock signals are less fatigued, have better moods, maintain healthier weights, gain more benefit from their medications, think more clearly, and have improved long-term health outcomes, said neuroscientist Russell Foster, who heads the Sleep and Circadian Neuroscience Institute at Oxford University in the UK. When we've been awake for a long time, our sleep drive kicks in and tells us we need to sleep.
The loop for sleep balances the 'sleep drive' with the need to be awake.
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