PROLOGUE: THE END OF THE WORLD IS NIGH!

Our ancestors were using fire, for heat, protection and light, between 300 000-400 000 years ago, before Homo sapiens evolved. Thus, for our entire history we have not been slaves to going to sleep with the rising and setting of the sun. The idea that this only happened recently, because of Edison and his lightbulb, is frankly ridiculous. The oldest evidence for something that specifically functioned as a bed dates back at least 77 000 years. Approximately 10 000 years ago we started building substantial structures, first in wood and later of stone, as our houses. Then about the same time we stopped believing in ghosts, witches and the devil, we started putting glass windows in our humble abodes. All these trappings of civilisation mean that we now sleep in an environment where

• There is a low risk from pathogens.
• We, and our livestock, are safe from predators and our enemies.
• We are dry and warm, without the need to tend the fire.
• We sleep privately with at most one other person, with little if any body contact.
• Our bedrooms are quiet, dark, fresh-smelling with access to clean fresh air.
• We sleep in a comfortable bed with clean dry bedding, free from biting parasites.
• We are secure behind locked and alarmed doors and windows so we no longer need someone to remain on watch or be woken by our guard dogs.
• The eight-hour day and working time directives exist to ensure we have adequate time for sleep.
• Computers and robots are promised to allow us to work even less.

These should be halcyon days for sleep.

However, it has been claimed that we are actually living in the midst of a 'catastrophic' sleep loss epidemic, which is having a 'catastrophic' impact on our health, our life expectancy, our safety and our productivity. Furthermore, claims are made that virtually every major disease is said to be linked to sleep loss and this lack of sleep is perhaps the greatest curable disease in the world right now.

Scary stuff I think you will agree, but is it actually true?

Well the first issue with this idea is one of definition, because it is not clear as to what the research is actually referring to when they talk about poor/ insufficient /short sleep. Is it people who naturally only need <6 hours sleep a night, i.e. they have a genetic disposition to short sleep, or is it someone who only sleeps <6 hours and by doing so is getting less sleep than they their genetics dictate. These are two different things, the first person cannot change nor can the risk of any negative effects, whereas the second person can, and probably should, change.

Are we really in the midst of a sleep-loss epidemic, 'catastrophic' or otherwise?

Despite what is claimed, there is actually very little reliable data about how we slept during the last hundred years and absolutely none from before that time. In light of all the recent scaremongering it is hard to believe that there is actually very little evidence to support the assertion that adult sleep duration has decreased in recent decades.

In a review of data from 15 countries from the 1960s until the 2000s, self-reported average sleep duration of adults was found to have actually increased in 7 countries: Bulgaria, Poland, Canada, France, Britain, Korea, and the Netherlands (range: 0.1-1.7 min per night each year) and decreased in 6 countries: Japan, Russia, Finland, Germany, Belgium, and Austria (but only by 0.1-0.6 min per night each year). Inconsistent results were found for the United States and Sweden. There was no clear social or economic grouping of the countries that might explain the diverse trends. So even where there has been a decrease in sleep duration it could hardly be considered 'catastrophic'.

A further study of data from 10 developed countries found that instead of the anticipated increase in short sleep, longer sleep durations had become more common across these nations. Short sleep had increased only in Italy and Norway but had decreased in Sweden, the United Kingdom, and the United States. Long sleep had increased in Australia, Finland, Sweden, the United Kingdom, and the United States but had decreased in Canada and Italy. No changes were observed in Germany or the Netherlands. The limited increases in short sleep duration challenge the claim of increasingly sleep-deprived societies, especially as long sleep has become more widespread than short sleep, at least when reported in time-use diaries. The worldwide decline in adult sleep duration seems to have been somewhat overstated.

A recent meta-analysis of objective sleep duration in healthy volunteers, as measured by polysomnography, (recording a person's brainwaves and other physiological variables in order to accurately measure sleep), also demonstrated that sleep time has not declined over the past 50 years.

But one might point out that the Centers for Disease Control and Prevention (CDC) states more than one third of US respondents reported typically sleeping less than 7 hours in a 24-hour period. While that may be true, it is only relevant firstly if you accept that fewer than 7 hours is the definition of short sleep and, secondly, if you can demonstrate using precisely the same survey methodology that there has been a change over time in the numbers of people having short sleep. Such data does not exist.

Is there evidence of a 'catastrophic' impact of poor sleep on our health, our life expectancy, our safety and our productivity?

The idea that an epidemic of insufficient sleep is a contributor to the development of major diseases, such as to Parkinson's, dementia, cancer, heart disease, obesity, diabetes, etc., rests largely on the question of whether sleep duration has declined in the last few decades. As shown above, evidence to support this notion does not in fact exist, at least in healthy sleepers.

Poor sleep may be associated with all of these illnesses, and doubtless many more, but a large study of middle-aged adults found that insomnia complaints did not predict an increased risk of death, nor interestingly did use of sleeping tablets.

The suggestion that there has been a 'catastrophic' impact of poor sleep on our life expectancy would seem hard to justify given the steady and significant increase in life expectancy over the last 150 years or so, for instance in the UK, data from the Office for National Statistics, has shown that over the last 100 years life expectancy at birth has increased by nearly 3 years per decade, essentially doubling since 1841.

Data from a large study showed that taking 7 hours sleep as the norm, people sleeping 6 hours had a 7% relatively greater risk of dying. This may seem to be worrying proof of the negative effects of short sleep on longevity, however this is not the whole story, the increased risk of dying in the group having 8 hours sleep was actually 12%, and for those sleeping 9 hours as much as 42% when compared to 7 hours.

With regards to safety, figures from the Bureau of Labor Statistics in the US shows that the number of non-fatal occupational injuries and illnesses per 100 full-time employees has fallen from 11 in 1973 to 2.9 in 2016.

Other data from the Bureau of Labor Statistics concerning productivity shows that US business sector output has increased more than ninefold since 1947 while the hours worked to produce that output have not quite doubled.

Of course, there are a number of contributory factors which account for the change in these figures, but to make the argument that there has been a 'catastrophic' effect of poor sleep seems problematic unless you are able to show that these figures would be appreciably different if we all slept better.

A survey attempted to quantify the benefit of the complete eradication of insomnia on work performance due to presenteeism, (this is where you are at work but are doing nothing productive), they found that it would lead to a reduction of between 5.4% and 7.8% of work performance lost.

A recent report found that a person sleeping less than six hours loses six more working days due to absenteeism or presenteeism per year than a worker sleeping seven to nine hours.

So, it is not really evident that there is a large negative impact of poor sleep, let alone one that is 'catastrophic'.

Is virtually every major disease linked to sleep loss?

Poor sleep may be linked with various diseases. However, these are associations not evidence of causation. Data from large studies mean that even a very small effect can become statistically significant, but that does not in any way mean that it is clinically relevant. For instance, data from the 'Sleep Heart Health Study' shows that people sleeping 6-7 hours had a significantly higher risk of hypertension that people sleeping 7-8 hours. However, the difference in blood pressure between the two groups was actually very small (systolic 2.1mmHg and diastolic 0.7mmHg).

Many of the modern-day illnesses such as Parkinson's, dementia,...