Modern sleep patterns 'mirror how our ancestors slept'
"Forget eight hours of sleep a night – we only actually need six," the Daily Mail reports. Research into hunter gatherer tribes suggests getting six to seven hours sleep a night may not be a modern phenomenon and is actually the norm for humans.
An ongoing concern about modern life is our sleep patterns are being adversely affected by the distractions of modern technology, such as smartphones, tablets and TVs. But, as the authors of this research highlight, similar concerns can be found in popular media dating back to the Victorian era.
To get a clearer picture of "pre-industrial" sleep habits, researchers studied three hunter gatherer communities who had no access to any of the trappings of modern life. These people were members of the Hadza (northern Tanzania), San (Namibia), and Tsimane (Bolivia) tribes.
The researchers found the hunter gatherers' sleep patterns were to a certain extent similar to those of the West – getting an average of 5.7 to 7.1 hours' sleep a night.
Sleep patterns seemed to mirror the temperature more than light levels. This finding could potentially help people with sleep disorders. The US National Sleep Foundation recommends a bedroom temperature of 18.3C (65F).
Interestingly, chronic insomnia was uncommon among the tribespeople – around 2% of tribespeople, compared with 10-30% in industrial societies. Two of the tribes actually had no word for insomnia in their language. This may suggest an active lifestyle can help prevent insomnia.
Where did the story come from?
The study was carried out by researchers from US universities, including academics from departments of anthropology, anatomical sciences, neurology and brain research, and psychiatry.
It was funded by US National Institutes for Health grants, the National Research Foundation of South Africa, and the National Science Foundation.
The study was published in the peer-reviewed journal Current Biology on an open-access basis, so it is free to read online or download as a PDF.
Headlines like the Daily Mail's – "Forget eight hours of sleep a night – we only actually need six" – and a similar headline in The Independent – "Six hours' sleep a night is enough, say scientists" – are not justified based on the results of this this study alone. The authors only studied sleep patterns. They make no recommendations about what sleep patterns are healthier.
Nonetheless, the Mail's statement that these "findings challenge [the] eight-hour rule" may be fair – a debate about the right amount of sleep is worth having, given the implications of this research. The next part of the sentence – "modern life is robbing us of sleep" – is largely subjective.
What kind of research was this?
This was an observational study of the natural sleep cycles in three non-industrial communities. The researchers say it has been argued that the invention of electric lighting, TV, the internet and related gadgetry, along with more caffeine use, has greatly shortened sleep duration from the "natural" levels that occurred before these modern changes.
The authors state this may have health implications. They report sleeping less has been linked to obesity, mood disorders and a "host of other physical and mental health illnesses thought to have increased recently".
With this in mind, they sought to establish what "natural" sleep patterns might be without the distractions of modern lighting, heating and electronic gadgetry.
In the absence of good data on sleep patterns from the past, they studied three non-industrial societies who live largely as hunter gatherers near the equator: the Hadza (northern Tanzania), the San (Namibia), and the Tsimane (Bolivia).
Studying these modern but non-industrialised groups, they hoped, would give an idea of the type of sleep patterns our ancestors might have had before mass migration to cities and the technological revolution.
What did the research involve?
The researchers collected data from 10 groups within three geographically different societies.
Participants wore watches that tracked their activity for between six and 28 days. The watches had been tested and validated, so they were able to detect when people were awake or asleep, as well as information on exposure to sunlight (mainly used to detect day and night sleeping habits).
Environmental temperature was measured by different devices attached to the middle fingers of both hands and the abdomen for the first four days of observation. These were also placed near where the participants slept to collect data on the temperature and humidity of their sleep environment, both in winter and summer.
On average, the participants were underweight or a healthy weight according to their body mass index (BMI). None of the people studied were overweight, a notable contrast to many industrialised societies.
The analysis looked at patterns of sleep onset and sleep duration in relation to light levels, seasons and temperature. Sleep onset is the length of time it takes to go from being fully awake to sleep – the "getting to sleep" phase.
Sleep duration is usually characterised by the time spent in either non-rapid eye movement sleep or rapid eye movement sleep, but in this study it was predicted based on how much people were moving, as detected by the watch.
What were the basic results?
All three groups showed similar sleep patterns. Sleep period – time including getting to sleep, sleeping and fully waking up – averaged 6.9 to 8.5 hours, with time spent fully asleep averaging around 5.7 to 7.1 hours. These were described as amounts near the low end of those of industrial societies.
On average, people slept an hour more in winter time than summer. None of the groups started trying to sleep near sunset – they averaged 3.3 hours after. Most woke an hour or so before sunrise, although there were examples of some waking after sunrise.
Napping wasn't particularly common, occurring in less than 7% of days in winter and less than 22% of days in summer.
How did the researchers interpret the results?
The researchers concluded that, "The daily cycle of temperature change, largely eliminated from modern sleep environments, may be a potent natural regulator of sleep."
Thinking about ways to use this knowledge to help people with sleep problems, they commented: "Mimicking aspects of the natural environment might be effective in treating certain modern sleep disorders."
Conclusion
This study of sleep patterns in non-industrialised communities indicates that sleep patterns in these communities might be more closely linked to environmental temperature and less linked to light, as had been assumed.
The use of objective sources of sleep, light and temperature information gives the study more reliability. However, the relatively short time period over which temperatures were measured – just four days – may not have given an entirely accurate picture.
Similarly, just three communities were studied – we can't assume this is representative of most non-industrialised communities. Also, the study does not take into account social and cultural attitudes to sleep, which could be a significant influencing factor.
The study notes light has been shown to be a major factor in human sleep. In this study, sleep occurred almost entirely during the dark period. This, the researchers say, contrasts with industrial populations, where sleep typically continues well after sunrise.
It is relatively common for people to have a dip in levels of alertness mid-afternoon, with some research suggesting this is unrelated to food intake.
As a result, the authors said they expected to see napping in this afternoon dip period as a natural remedy, a bit like a siesta – but they observed no such activity. This highlights how light and temperature don't predict all sleep patterns, so there must be additional explanations – possibly social – for these activities.
Often, what you do during the day can have a big influence on how well you sleep at night. Making sure you get plenty of exercise and minimising your consumption of caffeine and alcohol should help.
Read more advice on how to get a good night's sleep.
