Many of us wake up in the night, tossing and turning rather than sinking back into slumber.
This may be because our body clocks are better suited to two shorter chunks of sleep rather than for one long period, according to researchers.
Dr Melinda Jackson, a psychologist specialising in sleep disorders at RMIT University and c, said split sleeping used to be the norm, and going to bed for a continuous eight hours is a modern invention.
From medical texts to court records and diaries, throughout history there have been accounts of segmented sleep – and such patterns are seen today in cultures who take a siesta, they said.
Sleeping in two periods may increase alertness in the day and provide people with more flexibility to carry out work and spend time with their family, they said.
Writing for the Conversation, they explain the history of segmented sleeping, and why two slumbers might be better than one…
WAKING UP IN THE NIGHT USED TO BE THE NORM
Around a third of the population have trouble sleeping, including difficulties maintaining sleep throughout the night.
While night time awakenings are distressing for most sufferers, there is some evidence from our recent past that suggests this period of wakefulness occurring between two separate sleep periods was the norm.
Throughout history there have been numerous accounts of segmented sleep, from medical texts, to court records and diaries, and even in African and South American tribes, with a common reference to ‘first’ and ‘second’ sleep.
In Charles Dickens’ Barnaby Rudge (1840), he writes:
He knew this, even in the horror with which he started from his first sleep, and threw up the window to dispel it by the presence of some object, beyond the room, which had not been, as it were, the witness of his dream.
Anthropologists have found evidence that during preindustrial Europe, sleeping in two chunks was considered the norm.
Falling asleep was determined not by a set bedtime, but by whether there were things to do.
Historian A. Roger Ekirch’s book ‘At day’s close: night in times past’ describes how households at this time retired a couple of hours after dusk, woke a few hours later for one to two hours, and then had a second sleep until dawn.
During this waking period, people would relax, ponder their dreams or have sex.
Some would engage in activities like sewing, chopping wood or reading, relying on the light of the moon or oil lamps.
Ekirch found references to the first and second sleep started to disappear during the late 17th century.
This is thought to have started in the upper classes in Northern Europe and filtered down to the rest of Western society over the next 200 years.
Interestingly, the appearance of sleep maintenance insomnia in the literature in the late 19th century coincides with the period where accounts of split sleep start to disappear.
Thus, modern society may place unnecessary pressure on individuals that they must obtain a night of continuous consolidated sleep every night, adding to the anxiety about sleep and perpetuating the problem.
ARE TWO PERIODS OF SLEEP MORE NATURAL?
Less dramatic forms of this way of sleeping – called bi-phasic sleeping – are seen in today’s society, for example in cultures that take an afternoon siesta.
Our body clock lends itself to such a schedule, having a reduction in alertness in the early afternoon (the so-called ‘post-lunch dip’).
In the early 1990s, psychiatrist Thomas Wehr conducted a laboratory experiment in a group of people were left in darkness for 14 hours every day instead of the typical eight hours – for a month.
It took some time for their sleep to regulate but by the fourth week a distinct two-phase sleep pattern emerged.
They slept first for four hours, then woke for one to three hours before falling into a second four-hour sleep. This finding suggests bi-phasic sleep is a natural process with a biological basis.
SLEEPING IN TWO CHUNKS GIVES GREATER FLEXIBILITY
Today’s society often doesn’t allow for this type of flexibility, so we have to conform to today’s sleep/wake schedules.
It is generally thought a continuous seven to nine-hour unbroken sleep is probably best for feeling refreshed.
Such a schedule may not suit our circadian rhythms – our body clock – however, as we desynchronise with the external 24-hour light/dark cycle.
To successfully maintain a split sleep schedule, you have to get the timing right – that is commencing sleep when there is a strong drive for sleep and during a low circadian point in order to fall asleep quickly and maintain sleep.
Some of the key advantages of a split sleep schedule include the flexibility it allows with work and family time (where this flexibility is afforded).
Some individuals in modern society have adopted this type of schedule as it provides two periods of increased activity, creativity and alertness across the day, rather than having a long wake period where sleepiness builds up across the day and productivity wanes.
In support of this, there is growing evidence suggesting naps can have important benefits for memory and learning, increasing our alertness and improving our mood.
Some believe sleep disorders, like sleep maintenance insomnia, are rooted in the body’s natural preference for split sleep.
Therefore, split sleep schedules may be a more natural rhythm for some people.
‘TWO SLEEPS’ COULD HELP SHIFT WORKERS
Split-shift schedules that maintain adequate sleep time per 24 hours may be beneficial for sleep, performance and safety.
A number of recent studies have found split sleep provides comparable benefits for performance to one big sleep, if the total sleep time per 24 hours was maintained (at around seven to eight hours total sleep time per 24 hours).
However, as might be expected, performance and safety can still be impaired if wake up and start work times are in the early hours of the morning.
And we don’t know if these schedules afford any benefits for health and reduce the risk for chronic disease.
While the challenges of night shift work cannot be eliminated, the advantage of some split shift schedules is that all workers get at least some opportunity to sleep at night and do not have to sustain alertness for longer than six to eight hours.
Although we aspire to have consolidated sleep, this may not suit everyone’s body clock or work schedule.
It might in fact be a throwback to a bi-model sleep pattern from our pre-industrial ancestors and perhaps work well in a modern industrial setting.