Russell Foster—
In the 1980s sleep was for “wimps,” and generally regarded as “an illness in need of a cure.” By the 2000s sleep was starting to be taken seriously, and by 2020s sleep has become a major preoccupation for many, and “getting the perfect night of sleep” an obsession. Anxiety over our sleep has been fuelled by a stream of confusing information in the form of strident orders that resemble the commands of a Regimental Sergeant Major: You “must” get eight hours of sleep; waking up in the middle of the night is “bad;” you “must” be up at 7am or you will die! Sleep apps reinforce this anxiety with inaccurate information about the quality of our sleep. Rather than enjoying our sleep, it is now an endless cause of worry.
Yes! – sleep is an essential part of our biology, and not getting the sleep each of us needs will indeed harm our cognitive abilities, decision making skills, and our social interactions. Long-term sleep disruption can result in serious illnesses including Type-2 diabetes, immune suppression, cardiovascular disease, and even a greater risk of cancer. But “good sleep” is like shoe size, “one size does not fit all.” Whilst it is possible to make generalisations, taking an average value for sleep can be deeply misleading. How long we sleep, our preferred sleep times, and how many times we wake during the night vary both between individuals, and as we age.
Between the ages of 18 to 64 years, most of us sleep between seven to nine hours each night, but some perfectly healthily individuals sleep six or even 11 hours. After 64, average sleep is between seven to eight hours, but the full range can be between nine to five hours. Our ‘chronotype,’ refers to whether we are a “lark” (10% of the population), “owl” (25% of the population), or an in-between “dove” (65% of the population). But this changes with age. As teenagers and young adults, we tend to have later chronotypes, then move earlier in our middle and older years. We are often told that a single episode of sleep without waking (“monophasic” sleep) is normal. But it is not. Sleep can occur in two episodes (biphasic sleep) or even multiple episodes (polyphasic sleep), separated by short periods of wake, and this likely represents our ancestral pattern of sleep. Critically, if we wake at night, sleep is likely to return if it is not sacrificed to social media or worrying about not getting back to sleep!
So how do we know if we are getting enough sleep? It’s not complicated. If you can operate at a high level during the day, you are fine. However, if you’re need an alarm clock to get you out of bed; if you oversleep on free days; if you take a long time to wake up; if you feel sleepy and irritable during the day; if you crave a nap; if you need caffeinated drinks; and if you are less reflective and more impulsive, you are probably not getting enough sleep, and there is a lot that each of us can do, which I discuss in detail in my book, Life Time: Your Body Clock and Its Essential Roles in Good Health and Sleep.
But what about taking a nap or siesta? A siesta or short nap in the early afternoon, is historically common throughout the Mediterranean countries, Southern Europe, and Central China. The siesta has also been adopted in many countries where Spain had a historical influence like the Philippines and Hispanic American. A feature that unites all these places is a warm climate, and a large midday meal. Accommodating the siesta into modern industrial schedules is proving difficult in the cities of Spain and other countries, and there have been repeated calls by governments, and the business sector to abandon the practice all together. However, if you live in places like rural Spain, and the siesta is still part of the daily schedule, then embrace it! Sadly, most of us cannot. North American, Northern European, and the English-speaking nations, have largely adopted the view that a one to two-hour siesta in the afternoon is not appropriate, and cannot be accommodated into modern work schedules. So, what do you do if you feel tired in the afternoon and crave a nap? The first point to make is that if you want a nap you are probably not getting enough sleep at night, and that needs to be attended to first. However, if you enjoy a nap, then the occasional nap for no longer than twenty minutes is probably fine. Such short naps in sleepy individuals have been shown to improve the alertness and performance across the afternoon. Longer naps may be counterproductive as recovery from an extended nap can lead to feelings of grogginess, and lowered alertness for some time after the nap, and this is called “sleep inertia.” In addition, naps close to bedtime (within six hours or so) can act to reduce sleep pressure, and this will delay sleep at bedtime. This can be a big problem in some teenagers who go to sleep late, get-up tired, and struggle through the school day. A recent study in U.S. adolescents suggested that sleep disruption affects around 24% of students, and similar numbers have been reported in the U.K. After school in the afternoon, students arrive home, and then sleep for several hours. This reduces the sleep pressure and delays sleep that night, generating a vicious circle of later sleep times followed by longer naps in the late afternoon. The bottom line is that for most of us the occasional nap is fine, but be careful you don’t become dependent upon long day time naps. This will delay sleep at night, leading to shortened night time sleep, especially on work days where a lie-in is not possible.
In previous decades we have been rather arrogant about sleep, we think we can do what we want, at whatever time we choose. This assumption underpins the modern 24/7 society, and an economy that is dependent upon night shift workers, and a workforce that routinely experiences shortened sleep. We all try to squeeze more and more work into an already over-packed day. So, we push multiple activities into the night – leaving less time for sleep. But we are beginning to realize that we can’t do what we want at whatever time we choose. The point being that by embracing sleep and our individual sleep needs we can become “sleep wise.” And whilst the foolish and the wise all die in the end – the “sleep wise” will on average enjoy their sleep, be happier, less stressed, healthier, and, very possibly, live longer.
Professor Russell Foster is the Director of the Sleep and Circadian Neuroscience Institute at the University of Oxford. An acclaimed scientist, Foster has been elected to the Royal Society. Foster is the author of Life Time: Your Body Clock and Its Essential Roles in Good Health and Sleep, published by Yale University Press in 2022.
The Musics of Michel Leiris