Are we sleepwalking into a 'global sleep crisis'?

"We are facing a global sleep crisis because we don't go to bed early enough, say scientists," the Mail Online reports.

The warning comes from a study produced by a research team using a smartphone app (Entrain) to track sleep patterns from around the world.

The findings reveal that as people age, they tend to go to sleep earlier and wake later, and women tend to sleep more than men.

The researchers also found the timing of sunrise and sunset does influence sleep, but less than you might think.

Worldwide, there is a lot of variability in people's bedtime and the researchers believe this is down to social influences.

The researchers warn of a "global sleep crisis", but it is difficult to assess exactly what evidence this warning is based on.

The big stumbling block for this research is it can't provide us with any conclusive answers. It may be that factors such as using technical devices are disrupting our sleep, but we can't say anything about that based on this research.

Another drawback is that people chose to download this app. It could be that people with troubled sleep patterns would be more motivated to download the app than people with healthy sleep patterns.

Signs you may not be getting enough sleep include irritability and problems with concentration and memory. Persistent lack of sleep can make you more prone to accidents and chronic diseases.

Where did the story come from?

The study was carried out by researchers from the University of Michigan, and was funded by the Biomathematics Program at the Army Research Laboratory and the Human Frontier Science Program.

It was published in the peer-reviewed journal Science Advances on an open access basis, so it is free to read online or download as a PDF.

The Mail's headline, which says "we are facing a global sleep crisis", probably goes too far – the study provided no evidence to support the claims of an impending "sleep crisis". But, to be fair, this term was used in the study itself, but the researchers didn't elaborate on this.

What kind of research was this?

This cross-sectional study aimed to validate the use of mobile technology to collect information on sleep patterns worldwide, and explore the possible influences that social pressures have on sleep.

Sleep is known to be driven by our internal body clock. Naturally, sunrise and sunset would regulate this rhythm, but our modern lives are controlled by social factors, work obligations and artificial lighting, meaning we can't follow this natural rhythm.

As the researchers say, understanding the factors that control how much sleep we get is important as this can have a direct effect on human health.

In 2014 the researchers released a free app for iOS and Android devices – Entrain – that recommends optimal lighting schedules for adjusting to new time zones.

Users input data on their normal sleeping times, home time zone and typical lighting, sleep schedules and experience of jetlag.

In this study, the researchers analysed sleep habits from those who submitted data.

What did the research involve?

In 2014, the first year of the app's release, 8,070 users submitted data.

The researchers explained that when the app is loaded, the opening screen asks users their normal wake time and bedtime to the nearest hour, home time zone, and typical amount of light exposure.

The options for typical light were:

low indoor (200 lux)
bright indoor (500 lux)
low outdoor (1,000 lux)
bright outdoor (10,000 lux)

For the purposes of this study, the researchers combined the indoor categories into a single group and did the same for the outdoor ones.

Users were also asked to give data on age, gender and travel frequency (from several times a week to less than once a year). They could also record data on travel dates and experiences of jet lag.

The main countries contributing data were the US (45%), Australia (9%) and Canada (5%). The UK, France, Spain, the Netherlands, Denmark and Germany jointly contributed 15% of the data, and China, Japan and Singapore made up 5%.

The researchers excluded "outlier" data that was far from the norm: for example, those who woke before 3am or after 11am, who went to bed before 7pm or after 3am, or who had less than 4 or more than 12 hours' sleep a night. This means most shift workers would have been excluded.

They also excluded those aged under 18 or above 85. This left 5,450 people for analysis.

What were the basic results?

The adults analysed (majority male) represented a wide range of time zones, and more commonly reported indoor rather than outdoor light.

The researchers observed a relationship between age and sleep schedule, where in general increasing age was associated with less sleep and earlier waking times.

They found age has the strongest influence on the timing of midpoint of sleep, while gender had the strongest influence on duration of sleep, with women getting more sleep at nearly all ages.

Prior mathematical models suggested a later sunset and sunrise influence both bedtime and wake time, and the app data supported this. Sunrise after 6.30am and later sunset were both associated with later wake time and bedtime.

Later sunset was also associated with more sleep, particularly in the group who reported spending more time in outdoor light.

In general, women, older people and those with more outdoor light exposure seemed more sensitive to changes in sunset and sunrise than men, younger people and those with mostly indoor light exposure.

However, sunset timing had a weaker effect on bedtime than models may have predicted. The researchers considered that solar cues do influence sleep but may be ignored in the real world, particularly around bedtime.

The country the person resided in had an influence on their bedtime, suggesting that people are more responsive to social cues at night.

And sleep duration goes down as bed time becomes later. While average bedtime varied across countries, average wake time remained fairly consistent.

No results are reported for the influence of travel and reports of jet lag.

How did the researchers interpret the results?

The researchers noted that the trends they identified agree with previous large-scale surveys and laboratory studies, and validate the use of this mobile technology for assessing sleep.

They said that, "This work better defines and personalises 'normal' sleep, produces hypotheses for future testing in the laboratory, and suggests important ways to counteract the global sleep crisis."

Conclusion

These findings show that the app works, and it is possible for people to input data on the timing and duration of their sleep for researchers to get a global picture of sleep patterns worldwide.

The researchers noticed a number of themes, including that age, gender and the amount of time we spend outdoors are factors that can influence the timing and duration of sleep.

Timing of sunrise and sunset do seem to have an influence on our sleep, but less than may be expected. Across countries worldwide there is most variability in the time we go to bed, and this directly influences our sleep duration.

The researchers also considered that social influences are causing us to go to bed later and ignore the natural influences of sunset.

However, this is the big stumbling block of this research – it can't provide us with any answers, and we can only speculate as to why this is the case.

It may be that factors such as late-night working, socialising or using technical devices are influencing our sleep, but we can't say anything about that based on this research.

Another limitation of the study is that excluding people with outlying sleep patterns – very late bed times or waking times – automatically excludes shift workers. This is often the group in which previous research has speculated disrupted sleep patterns could have an adverse effect on health.

There is also the potential for misclassification when people are asked to categorise their typical light exposure as indoor or outdoor. There is likely to be wide variation in the amount of natural daylight that people in these two broad categories are exposed to.

A final important limitation is that the population were self-selecting. People actively chose to download and use the application, meaning the study could be at risk of selection bias.

Arguably, people with sleep problems are more likely to download a sleep app than people without sleep problems, so the results may not be truly representative.

It is also worth noting that only a fraction of the data analysed comes from the UK, so the study can't give any great insight into this country's sleep patterns and influences.

Overall, the findings are undoubtedly of interest in furthering understanding of the world's sleep patterns. However, they raise more questions than answers on how our social and working lives are affecting our sleep and health.