It is generally recommended that people get 7-9 hours of sleep per day but it is not clear that the benefits that accrue from sleep are lost if those hours are not in one block. Like many people, I often wake up very early morning before it is light outside and try to go back to sleep immediately, usually with some success unless something is on my mind that prevents me from falling asleep for some time. I used to think that this pattern of two blocks of sleep per night with a brief break was an aberration and that ‘normal’ sleep should consist of roughly eight hours of uninterrupted sleep.
But recently I have been intrigued by articles that summarize research that it is the one long sleep that is unusual and came about as a result of electric light becoming ubiquitous, and that before that nighttime sleep was in two parts separated by one to three hours of wakefulness in which people did whatever they wanted to needed to do. I wrote about this over seven years ago and now comes another article along these lines is by Karen Emslie that updates some of the information.
Modern, electrical illumination revolutionised the night and, in turn, sleep. Prior to Edison, says the Virginia Tech historian A Roger Ekirch, author of At Day’s Close: Night in Times Past (2005), sleep had been divided into two distinct segments, separated by a period of night-waking that lasted between one and several hours. The pattern was called segmented sleep.
Sleep patterns of the past might surprise us today. While we might think that our circadian rhythm should wake us only as the sun rises, many animals and insects do not sleep in one uninterrupted block but in chunks of several hours at a time or in two distinct segments. Ekirch believes that humans, left to sleep naturally, would not sleep in a consolidated block either.
Before electric lighting, night was associated with crime and fear – people stayed inside and went early to bed. The time of their first sleep varied with season and social class, but usually commenced a couple of hours after dusk and lasted for three or four hours until, in the middle of the night, people naturally woke up. Prior to electric lighting, wealthier households often had other forms of artificial light – for instance, gas lamps – and in turn went to bed later. Interestingly, Ekirch found less reference to segmented sleep in personal papers from such households.
When people wake up around 3:00 or 4:00am, they often try to force themselves back to sleep and get stressed when they cannot, which hinders sleep even further. Emslie suggest that we should embrace that early morning wakefulness to do various things before going back to sleep. The catch is that our work days often require us to get out of bed at around 6:00am or so and that prevents us from finding time for a couple of hours of activity before the second sleep block. Of course, we could go to bed earlier like people used to do, say around 8:00pm, and then when we wake up after four hours of sleep, we can do stuff for about two hours and then get another four hours of sleep before waking. In other words, we shift what we would normally do in the late evening to the middle of the night.
But so much of modern life is centered around the late evening hours that this two-sleep routine may not be feasible except for the few who can sleep until later in the morning. Now that I am retired and can sleep as late as I want, I am tempted to try this out because it will still allow me to keep to my current bed time of around 11:00pm.
Via Seamus Bellamy, I came across this fascinating video by former NASA astronaut Mike Massimino about sleeping in space. He says that the astronauts are encouraged to work on an Earth schedule of 24 hour ‘days’ even though a ‘day’ in orbit only lasts 90 minutes. This regimen includes encouraging them to sleep for eight hours. I wonder if the astronauts might be better off being advised to sleep in two blocks of four hours with activity in between.