“What’s the right amount of sleep I need? Should I be drinking cherry juice to sleep better? Why do you keep ignoring my voicemails?”
In the absence of being asked about dreams, people are generally keen to hear my views on how to get the best sleep possible. I think this is a fair question to ask a sleep scientist. I’m less convinced that you’ll get an accurate answer from a mattress salesman – but maybe that’s just me. A normal night’s sleep typically involves a single block from the moment our heads hit the pillow to when we feel our way towards our phone alarm in the morning. The number of hours sleep will vary but this will probably be somewhere between 7 to 9 hours (it may be slightly more or less than this). Hopefully, you’ll also feel fairly refreshed after waking up. Many of us still feel tired the following day for a myriad of reasons and will seek some solution for how to feel more energetic, creative and productive. One sleep buzzword which has attracted many such sleep perfectionists is ‘biphasic sleep’ and it involves splitting up our usual undisturbed bout of sleep.
For some people, sleep is experienced as two (or more) bouts of slumber throughout a night. For these biphasic sleepers, they will enjoy an initial sleep followed by a period of wakefulness and then finish off the night with their second sleep. Unlike those of us who restlessly wake up in the middle of the night and feel awful the following day, biphasic sleepers feel fully refreshed with their fragmented pattern. Some natural biphasic sleepers can even mistake their wakefulness for insomnia and this can cause its own problems.
There is some evidence that biphasic sleep is everyone’s normal sleep patterns but artificial lighting has forced us to sleep in one undisturbed bout. However, the scientific evidence to back this up has been somewhat sluggish. It wasn’t until late into the 20th century that our capacity for a biphasic sleep schedule was brought to light.
In the early 1990s, the psychiatrist Thomas Wehr showed that individuals under strict lighting conditions shifted from a single block of sleep to sleeping in a more segmented fashion. In his sample of eight healthy white men, Wehr had them spend 4 weeks under ‘winter’ lighting conditions whereby they had 10 hours of light a day. Then, as a comparison condition, the participants were exposed to 16 hours light and 8 hours dark to broadly mimic summer lighting for a single week. Under summer lighting conditions, the participants slept in one single block and appeared to be largely consistent in their sleeping patterns. However, when they were required to spend a month in the winter lighting pattern, they showed fragmented sleep that was typically, but not always, split in two or more segments (e.g. biphasic). This suggests that provided the period of darkness is long enough, such as experienced during the winter months, then the sleep period will start to be split up over a typical night. As a result, advocates of biphasic sleep as the optimum sleep schedule frequently quote this study as concrete evidence for their point of view.
It’s important to note a few things about this commonly referenced study. In the ‘winter’ condition, participants were told they could do not do anything active during the dark periods (e.g. listen to music or exercise). They were not allowed to use artificial lighting and were encouraged to rest during the dark period. This didn’t leave much choice but to sleep during this 14-hour window. Therefore, biphasic sleep might be seen because the participants had nothing better to do than go back to sleep if it was still dark upon awakening.
This was the same conclusion put forward by a study published in 2015 which also argued that a switch to biphasic sleep may simply be a result of long winter nights. Not everyone agrees so readily with this interpretation. However, until more convincing research is forthcoming it looks like we shouldn’t be trying to wake ourselves up at 2am every morning for that mid-sleep conference call. There is no evidence (as always please try to prove me wrong) that splitting your sleep into two segments is better than sleeping in a single block. Current advocates of biphasic sleep tend to singularly use Wehr’s study as evidence for their points without acknowledging the caveats to his study.
So, that still leaves the question remaining why some groups are advocating splitting up your sleep into small segments if the evidence is lacking. Well, besides our obsession with being told exactly how much of everything (e.g. fruit, water, sleep, fun) we are supposed to have there is a common theme to those keen to split up their sleep – they want to sleep less. Madness, I know.
Terms such as biphasic and polyphasic are frequently kidnapped against their will to lend legitimacy to schedules such as Everyman and Uberman schedules. These sleep schedules aim to break the day into small naps so that people can work unhindered by something as trivial as sleep. To put this into context, the Uberman schedule involves sleeping no more than 2 hours broken neatly up into 6 separate 20-minute naps – sounds lovely, doesn’t it? Well… By contrast, the Everyman schedule allows you 3 hours of sleep followed by 3 naps of 20 minutes throughout the day. So, you get a whole 4 hours sleep with this approach. I will save why these schedules are ridiculous for another post, but I’ve included them to illustrate that interest in segmenting the night’s sleep overlaps considerably with ‘hacking’ the numbers of hours of sleep we need in a day.
As I’ve hopefully make clear so far, sleep is important – all of it. Hacking your sleep will leave you exhausted and at an increased risk for multiple physical and mental illnesses. If you’re interested in feeling more energetic, perhaps think about whether sleep really is the culprit. Alternatively, maybe stop reading these blog posts at 2am and sleep. Actually, on second thoughts…
WEHR, T. A. (1991). The durations of human melatonin secretion and sleep respond to changes in daylength (photoperiod). The Journal of Clinical Endocrinology & Metabolism, 73(6), 1276-1280.
Ekirch, A. R. (2016). Segmented sleep in preindustrial societies. Sleep, 29 (3), 715-716.
Yetish, G., Kaplan, H., Gurven, M., Wood, B., Pontzer, H., Manger, P. R., … & Siegel, J. M. (2015). Natural sleep and its seasonal variations in three pre-industrial societies. Current Biology, 25(21), 2862-2868.