Two sleeps may be better than one

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Getting a good night’s sleep is often thought to mean having 7 or 8 hours of uninterrupted sleep before waking in the morning rested, refreshed and ready to face the day. However, a growing body of historical evidence suggests that it may be perfectly natural to sleep for a few hours, wake for a period, then go back to sleep.

By analysing diaries, letters, artwork, court records, medical textbooks and works of literature, historians Roger Ekirch and Craig Koslofsky have shown that as recently as 200 years ago the sleeping patterns of Europeans differed radically from those of today.

Historical records indicate that most people slept in 2 distinct chunks known as the “first sleep” and “second sleep”. They went to bed shortly after sundown and slept until past midnight, then woke up and spent a few hours in a state of quiet wakefulness before going back to sleep for a shorter period until morning.

Between each sleep most people would stay in bed and read, write, pray, talk or have sex. Others were more active and would get up to take a walk, go to the toilet or do housework. Some people even visited neighbours, brewed beer, tended livestock and engaged in petty thievery during the interlude between each sleep.

It is clear that people commonly awoke periodically during the night without perceiving this as a sleep interruption or problem. Indeed, it appears that in the past segmented sleep was regarded as a fact of life that was as ordinary as breakfast.

This began to change in the late 1600s, when references to the first and second sleep started to disappear amongst the upper classes of northern Europe. This spread to the rest of society by the 1850s. During the industrial revolution artificial lighting became increasingly widespread and people started to go to bed later. It is thought that staying awake long after sundown led people to be so chronically sleep deprived that they began to sleep for long uninterrupted stretches each night.

Historians also suggest that a concern with efficiency and productivity meant that spending hours lying in bed became regarded as a waste of time. For the time-conscious Victorians, the sleeping habits of their pre-industrial forebears were seen as laziness – far better to instead sleep for a single stretch then wake up and get on with work.

Regardless of the cause, by the 1890s the terms “first sleep” and “second sleep” had disappeared from common use altogether. Around this time a new disorder called sleep maintenance insomnia, in which people wake during the night and have trouble getting back to sleep, first appeared in medical literature.

This may indicate that uninterrupted sleep patterns became the new norm so when the natural pattern of sleeping in two shifts reasserted itself, it was regarded as abnormal and distressing. This suggests biphasic sleep may be the most natural sleep state for humans and that disruptions to this may be the cause of medically-diagnosed sleep problems.

This effect was confirmed when psychiatrist Thomas Wehr conducted an experiment in the early 1990s in which a group of people were plunged into darkness for 14 hours every day for a month. It took some time for their sleeping rhythms to readjust and the participants initially slept for about 11 hours to compensate for a sleep debt. However, by the fourth week the subjects had settled into a very distinct pattern that was consistent with the sleeping habits of people from pre-industrial times. They slept first for 4 hours, then woke for a few hours before falling into a second 4 hour sleep.

Similar results have been found by sleep researchers at the National Institute of Mental Health in the US and by anthropologists in Nigeria, where traditional societies also practice biphasic segmented sleep and use the terms “first sleep” and “second sleep” to refer to specific periods of the night.

Altogether, this evidence suggests that periodic wakefulness is part of normal human physiology. Some medical researchers and historians are beginning to think that this segmented sleeping pattern might actually be more beneficial than the modern “consolidated” or monophasic ideal of 7 to 8 straight hours currently championed by doctors. Sleep scientists have even suggested that the waking period between sleeps, when people engaged in periods of rest and relaxation, played an important role in our capacity to regulate stress.

The popular modern assumption that consolidated sleep with no awakenings is the normal and correct way for human adults to sleep may lead people to worry that they have sleep maintenance insomnia if they frequently awaken during the night. Worrying about being tired and fatigued the next day may paradoxically make it harder to get back to sleep.

Their concerns might best be addressed with a reassurance that their sleep conforms to historically natural patterns. Rather than becoming anxious upon waking in the middle of the night, it is far better to spend a quiet hour or so on a pleasant activity before going back to bed for the “second sleep”.

Image credit

Puvis de Chavannes, P. (1867). Sleep [Image]. Retrieved from https://www.flickr.com/photos/mazanto/14292545723

References

BaHamman, A., Sharif, M., Spence, D., & Pandi-Perumal, S. (2012). Sleep architecture of consolidated sleep and split sleep due to the dawn (fajr) prayer among Muslims and its impact on daytime sleepiness. Annals of Thoracic Medicine, 7(1), 36-41. Retrieved from PubMed Central.

Ekirch, A. E. (2005). At day’s close: night in times past. New York: Norton.

Koslofsky, C. (2011). Evening’s empire: a history of the night in early modern Europe. New York: Cambridge University Press.

Wehr, T. A. (1992). In short photoperiods human sleep is biphasic. Journal of Sleep Research, 1(2), 103-107. Retrieved from Science Direct.

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