Biphasic Sleep

Until recently, the supremacy of 8 to 9 hours of uninterrupted sleep for optimum health has gone unchallenged, but forthcoming research indicates that biphasic sleep might be just as good, if not better for human health!

A peaceful night of continuous sleep seems to be the elusive goal that doctors recommend and that we are all hoping to obtain. Yet many of us, despite following the advice of sleep therapists or owning a comfortable mattress, continue to wake up in the middle of night.

To compound matters, random waking can cause anxiety about getting enough rest before work the next day, making falling back to sleep that much more difficult. Recent research, however, may explain this late-night tossing and turning and perhaps shed light on one of the causes of elevated stress levels in modern society.

In At Day’s Close: Night in Times Past, historian Roger Ekirch reveals that before the Industrial Revolution, people used to sleep in two distinct chunks, which people from the time referred to as “first sleep” and “second sleep.” Psychiatrists and other researches call this type of sleep cycle “biphasic” or “bi-segmented.” A biphasic sleep pattern has been observed among some primitive cultures, as well as in various animals, but until now it was assumed that most people throughout history slept once per day for a continuous length of time. It turns out, however, that before the invention of electricity, people were more in-tune with the natural rhythms of light and dark in creation.

While reading hundreds of documents from the early modern period (1500-1800), Ekirch noticed that people repeatedly referred to a “first” and “second” sleep, as well as a period of semi-wakefulness in-between sleeps. People would usually wind down for bed as soon as it started to grow dark, fall-asleep for about 4 hours, wake for 1 to 3 hours, and then fall back asleep for another 4 or more hours. Further research revealed that this biphasic sleep pattern was quite common and that the time between “first” and “second” sleeps was used for a variety for purposes.

After a long day of work, “the time between sleeps” was the best time for peace and relaxation, or visiting with loved ones or friends. For others, such a writers and philosophers, it proved ideal for thinking and journaling. Doctors advising married couples on how to conceive, recommended late night wakefulness as a good time for conception, as it was during this period that the couple would be most relaxed and rejuvenated. Psychiatrist Walter Brown believes that such a sleep schedule may have helped people better cope with the stresses of daily life.

The tendency for humans to sleep in two phases in the lack for artificial light was also confirmed by several experiments conducted by psychiatrist Dr. Wehr. In one experiment in-particular, Dr. Wehr found that when individuals went from receiving 16-hours of light exposure (what most experience as a result of artificial lighting) to only 10-hours of light exposure per day (equivalent to a winter day without any artificial light), the subjects’ sleep cycles naturally split into two distinct periods with 1-3 hours of wakefulness in-between.

This rediscovery about the human tendency towards a biphasic sleep cycle is very interesting, especially in light of our modern habits. But what are we supposed to do with this knowledge? At this point it’s difficult to say for sure; going without artificial lighting might be a fun experiment, but for most of us it’s unrealistic. If anything, maybe we can try to live a little more with the rhythms of creation by turning the lights or TV off a bit earlier at night. Or, the next time one of us wakes up in the middle of the night, we might find some solace in the knowledge that it could be because of the body’s natural sleep cycle.

Research continues to reveal how technology and societal “advancements” affect our health in unforeseen (and often negative) ways. The more we trust in God’s provision and enjoy the goodness of his creation, the healthier we will become.

References: At Day’s Close: Night in Times Past, by Roger Ekrich; In short photoperiods, human sleep is biphasic. Dr. TA Wehr; Acknowledging Preindustrial Patterns of Sleep May Revolutionize Approach to Sleep Dysfunction Dr. Walter Brown

Recommended Reading: The Neuroscience of Sleep with Russell Foster

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