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The Cost of Nocturia in Europe

Hypothesis / aims of study
Nocturia is common and can have a profoundly negative effect on those living with the condition, mainly due to its impact on sleep. Nocturia is the leading cause of sleep disruption in adults aged ≥55 years, but the consequence of poor sleep as a result of nocturia is often overlooked. Poor sleep leads to deficits in daily functioning, productivity and overall quality of life (QoL). The sleep fragmentation experienced by people with nocturia, especially when difficulties falling back to sleep are encountered, might help to explain the wide-ranging negative impact of the condition.
Since nocturia is believed to be an inevitable part of the aging process and not a serious medical condition, it is often regarded as a trivial ‘QoL problem’ which does not require treatment. It is therefore important to conduct a cost-of-illness calculation to investigate the economic consequences of nocturia. If there is significant cost to society caused by nocturia, the disease is no longer only relevant for the affected individual/family – it becomes a wider societal concern. This may impact upon the perception of nocturia and be of relevance in consideration of whether proactive treatment or ‘watchful waiting’ is the most appropriate strategy.
US data show that failing to treat nocturia leads to a large economic burden on society; however, these results cannot be translated to Europe as healthcare systems are very different in the USA and in Europe. Therefore, the aim of this study was to establish the cost implications of failing to treat nocturia in a European context. Reduced work productivity and increased falls are the two main sources of cost associated with nocturia which require consideration when calculating the economic burden of the condition.

Study design, materials and methods
Based on the Epidemiology of LUTS (EpiLUTS) data, ≥12.9% of men and 15% of women experience severe nocturia (≥3 voids/night) at least ‘often’. European data on working hours and average salaries were obtained from EUROstat.
The impact of nocturia on work productivity was calculated using published data from population surveys of both absenteeism and productivity in professionally active adults with nocturia compared with controls. The work productivity and activity impairment questionnaire was used (1). The net impairment of 9.19% (0% = maximum productivity; 100% = total loss of work productivity) was based on subjects who had ≥1 void/night in the population survey; however, to ensure a modest estimate, this level of impairment was attributed to those who had ≥3 voids/night in this study.
To assess the impact of nocturia on falls we estimated the proportional population risk from a study on hip fractures in elderly (≥65 years) nocturia patients, showing a prevalence of 1.38% and 1.52% per year for men and women, respectively (2). This was applied to the estimated EU mean cost of hospitalization for a hip fracture (8500 €) (3) to establish the total cost attributable to nocturia.

Results
Based on prevalence rates from the EpiLUTS study, approximately 7 million men and 8 million women aged between 40 and 65 years have ≥3 voids/night in Europe (defined as EU-15: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, the Netherlands, Portugal, Spain, Sweden and the UK).
Table 1 shows the estimated loss of productivity per year for men and women living with severe nocturia based on a reduction in work productivity of 9.19%. In total, nocturia costs approximately €29 billion per year.
Of the 24 million men and 33 million women ≥65 living in EU-15, approximately 3 million men and 5 million women suffer from ≥3 voids/night (severe nocturia) according to the EpiLUTS data. Applying the proportional population risk of breaking the hip due to severe nocturia (≥3 voids/night) approximately 43,000 men and 76,000 women per year will break a hip in EU-15 due to nocturia (see Table 2). The estimated total cost of hospitalization for hip fractures due to severe nocturia per year in EU-15 is approximately €1 billion.

Interpretation of results
It is difficult to conduct a cost of illness study in Europe because the European countries are very different. However, it is still interesting to compare the cost of nocturia in Europe with that in the USA. Since it was necessary to use many average values in our calculations, we have been as conservative as possible with the values incorporated into the model. Prevalence data used were for individuals with ≥3 voids/night (severe nocturia only). Although the prevalence rate (12.9% of men and 15% of women) is based on a sample of individuals aged 40–99 years and includes people above working age, it is still lower than in most other epidemiology studies. In addition, only hip fracture data were used for falls. These numbers are more reliable because a hip fracture must be treated in hospital and there are studies correlating nocturia and hip fractures. The current study, therefore, presents a conservative estimate because all other types of falls are not included. Lastly, the estimate is based upon data from the EU-15 countries only, since these have a more similar price level than some of the wider European Union countries (eg Bulgaria), and the average values therefore do not cover extreme outliers.

Concluding message
These findings demonstrate that nocturia represents a very significant economic burden for EU-15 society, especially due to a decrease in productivity. This cost estimate challenges preconceived notions about nocturia that it should not be treated because it is a natural part of the aging process. The costs associated with nocturia indicate that whether or not nocturia is treated is not just a matter of relevance for the QoL of affected individuals, but is a wider societal concern.
Table 1: Economic burden of nocturia in Europe due to loss of work productivity in patient <65 (average European wage based on full-time employees in ‘industry and services’ with ≥10 employees).
Men
Women
Average wage per hour
€14.1
€10.9
Productivity loss per person
180 hours
143 hours
Value of total lost productivity in EU per year
€17,753,966,984
€10,918,327,646
Table 2: Economic burden of nocturia in Europe due to hip fractures in nocturia patients ≥65.
Men
Women
Mean cost of total hospitalization cost due to hip fracture
€ 8500
€ 8500
Number of nocturia patients (≥3 voids/night) suffering hip fracture
43,103
75,931
Total cost of hip fractures due to nocturia per year
€366,371,964
€645,409,339

Frequent Urination at Night Linked to Raised Death Risk

People who wake up frequently during the night to urinate are at an increased risk of death even after accounting for chronic conditions that are known to cause the problem, two new studies show.

The findings, scheduled to be presented Sunday at the American Urological Association’s annual meeting in San Francisco, suggest that frequent urination at night, or nocturia, is a predictor of mortality in adults of all ages rather than just the elderly, and that other unrecognized medical conditions may be contributing factors.

In the first study, researchers at the New England Research Institutes in Watertown, Mass., examined the health records of nearly 16,000 men and women aged 20 and older, and found that those who woke up to urinate two or more times a night had a higher risk of mortality than those who made less than two nighttime bathroom trips. The association between nocturia and mortality remained even after adjusting for coexisting conditions, such as diabetes and cardiovascular disease, and was stronger in those aged 20 to 64 than it was in those aged 65 and older.

“In the younger age group, those who reported having nocturia had roughly twice the risk of mortality as those without, while in the older age group nocturia increased the risk in the range of 20 to 30 percent,” said study author Varant Kupelian, a research assistant at the New England Research Institutes.

Kupelian and colleagues examined records from the Third National Health and Nutrition Examination Survey (NHANES III) conducted between 1988 and 1994, as well as death certificate data in the National Death Index through Dec. 31, 2000. In the study group of 15,988 men and women, the prevalence of nocturia was 15.5 percent among men and roughly 21 percent among women, and increased rapidly with age.

Kupelian said the greater risk of mortality in younger adults “suggests that nocturia may be a marker or warning sign for subclinical disease or for the impending development of chronic disease.” He added that the higher mortality risk in older adults may also be partly due to falls and fractures that occur when people get up to go to the bathroom in the middle of the night.

The second study, by researchers at Tohoku University School of Medicine in Sendai, Japan, examined a group of elderly residents living in an urban district of north Japan and resulted in findings similar to the U.S. study. After conducting extensive health assessments of 788 men and women aged 70 and older, and then tracking mortality data on them for five years, Dr. Haruo Nakagawa and colleagues found a significantly increased risk of mortality associated with frequency of nighttime urination, even after adjusting for several factors that could contribute to mortality. They also found that the more times a person got up to urinate at night, the higher the risk of mortality.

“Both of these studies are showing a connection between nocturia and mortality, and now the next step is to try to identify what the underlying factors are that are causing this association,” said Dr. Tomas L. Griebling, vice chair of the department of urology at the University of Kansas School of Medicine in Kansas City.

In the meantime, said Griebling, the message for patients is “don’t be alarmed if you’re getting up two or three times a night. It doesn’t mean you’re going to die. But it is something you should tell your health care provider about, because it may be due to an underlying health condition.”

Poor Sleep Associated With Higher Risk of Chronic Pain

People who sleep poorly may be more likely to develop a chronic pain condition and have worse physical health, a study from the UK suggests.
A general decline in both the quantity and quality of hours slept led to a two- to three-fold increase in pain problems over time, researchers found.
“Sleep and pain problems are two of the biggest health problems in today’s society,” said lead study author Esther Afolalu of the University of Warwick in Coventry.
Pain is known to interfere with sleep, she told Reuters Health by email. But the new study shows “that the impact of sleep on pain is often bigger than (the impact of) pain on sleep,” she said.

Sleep disturbances, she added, contribute to problems in the ability to process and cope with pain.
Afolalu and colleagues reviewed 16 studies involving more than 60,000 adults from 10 countries. The studies looked at how well people were sleeping at the start, and then evaluated the effects of long-term sleep changes on pain, immune function and physical health. Half the participants were tracked for at least four and a half years.
Overall, sleep reductions led to impaired responses to bacteria, viruses and other foreign substances, more inflammation, higher levels of the stress hormone cortisol and other biomarkers related to pain, fatigue and poor health. Newly developed insomnia doubled the risk of a chronic pain disorder and hip fracture problems, the study authors wrote in the journal Sleep Medicine, online August 18.
Deterioration in sleep was also associated with worse self-reported physical functioning.

At the same time, researchers didn’t find links between increased sleep and less pain or arthritis, although they did find that improvement in sleep was associated with better physical functioning.
One limitation of the analysis is that the studies relied on participants to recall their own sleep patterns. Also, the studies didn’t all use the same tools to measure sleep quality and quantity.
Future studies should look at sleep patterns for different groups of people and how that affects health, Afolalu said. Her team is now analyzing data from the UK Household Longitudinal Survey to understand sleep, insomnia and health for people with arthritis.
Additional studies should also investigate how sleep deficiency leads to chronic pain disorders, said Dr. Monika Haack, who studies sleep, pain and inflammation at Harvard Medical School’s Human Sleep and Inflammatory Systems Lab in Boston.

Haack, who wasn’t involved with the new research, said in an email, “It is also important to identify whether there is a specific sleep pattern that is most dangerous for pain. For example, does sleep disruption (with frequent, intermittent awakening throughout the night) have a higher impact than a short but consolidated sleep?”

Haack and colleagues recently reported in the journal Pain that restricting sleep on weekdays and catching up on the weekends led to more pain. Furthermore, people who caught up on weekends had a tougher time dealing with pain than those who slept eight hours every night.

“In those already suffering from chronic pain, it is of critical importance to incorporate sleep improvement strategies,” Haack said. “And to have sleep specialists as part of the pain management team.”

The shorter your sleep, the shorter your life: the new sleep science

Matthew Walker has learned to dread the question “What do you do?” At parties, it signals the end of his evening; thereafter, his new acquaintance will inevitably cling to him like ivy. On an aeroplane, it usually means that while everyone else watches movies or reads a thriller, he will find himself running an hours-long salon for the benefit of passengers and crew alike. “I’ve begun to lie,” he says. “Seriously. I just tell people I’m a dolphin trainer. It’s better for everyone.”
Walker is a sleep scientist. To be specific, he is the director of the Center for Human Sleep Science at the University of California, Berkeley, a research institute whose goal – possibly unachievable – is to understand everything about sleep’s impact on us, from birth to death, in sickness and health. No wonder, then, that people long for his counsel. As the line between work and leisure grows ever more blurred, rare is the person who doesn’t worry about their sleep. But even as we contemplate the shadows beneath our eyes, most of us don’t know the half of it – and perhaps this is the real reason he has stopped telling strangers how he makes his living. When Walker talks about sleep he can’t, in all conscience, limit himself to whispering comforting nothings about camomile tea and warm baths. It’s his conviction that we are in the midst of a “catastrophic sleep-loss epidemic”, the consequences of which are far graver than any of us could imagine. This situation, he believes, is only likely to change if government gets involved.

Walker has spent the last four and a half years writing Why We Sleep, a complex but urgent book that examines the effects of this epidemic close up, the idea being that once people know of the powerful links between sleep loss and, among other things, Alzheimer’s disease, cancer, diabetes, obesity and poor mental health, they will try harder to get the recommended eight hours a night (sleep deprivation, amazing as this may sound to Donald Trump types, constitutes anything less than seven hours). But, in the end, the individual can achieve only so much. Walker wants major institutions and law-makers to take up his ideas, too. “No aspect of our biology is left unscathed by sleep deprivation,” he says. “It sinks down into every possible nook and cranny. And yet no one is doing anything about it. Things have to change: in the workplace and our communities, our homes and families. But when did you ever see an NHS poster urging sleep on people? When did a doctor prescribe, not sleeping pills, but sleep itself? It needs to be prioritised, even incentivised. Sleep loss costs the UK economy over £30bn a year in lost revenue, or 2% of GDP. I could double the NHS budget if only they would institute policies to mandate or powerfully encourage sleep.”

Why, exactly, are we so sleep-deprived? What has happened over the course of the last 75 years? In 1942, less than 8% of the population was trying to survive on six hours or less sleep a night; in 2017, almost one in two people is. The reasons are seemingly obvious. “First, we electrified the night,” Walker says. “Light is a profound degrader of our sleep. Second, there is the issue of work: not only the porous borders between when you start and finish, but longer commuter times, too. No one wants to give up time with their family or entertainment, so they give up sleep instead. And anxiety plays a part. We’re a lonelier, more depressed society. Alcohol and caffeine are more widely available. All these are the enemies of sleep.”
But Walker believes, too, that in the developed world sleep is strongly associated with weakness, even shame. “We have stigmatised sleep with the label of laziness. We want to seem busy, and one way we express that is by proclaiming how little sleep we’re getting. It’s a badge of honour. When I give lectures, people will wait behind until there is no one around and then tell me quietly: ‘I seem to be one of those people who need eight or nine hours’ sleep.’ It’s embarrassing to say it in public. They would rather wait 45 minutes for the confessional. They’re convinced that they’re abnormal, and why wouldn’t they be? We chastise people for sleeping what are, after all, only sufficient amounts. We think of them as slothful. No one would look at an infant baby asleep, and say ‘What a lazy baby!’ We know sleeping is non-negotiable for a baby. But that notion is quickly abandoned [as we grow up]. Humans are the only species that deliberately deprive themselves of sleep for no apparent reason.” In case you’re wondering, the number of people who can survive on five hours of sleep or less without any impairment, expressed as a percent of the population and rounded to a whole number, is zero.
The world of sleep science is still relatively small. But it is growing exponentially, thanks both to demand (the multifarious and growing pressures caused by the epidemic) and to new technology (such as electrical and magnetic brain stimulators), which enables researchers to have what Walker describes as “VIP access” to the sleeping brain. Walker, who is 44 and was born in Liverpool, has been in the field for more than 20 years, having published his first research paper at the age of just 21. “I would love to tell you that I was fascinated by conscious states from childhood,” he says. “But in truth, it was accidental.” He started out studying for a medical degree in Nottingham. But having discovered that doctoring wasn’t for him – he was more enthralled by questions than by answers – he switched to neuroscience, and after graduation, began a PhD in neurophysiology supported by the Medical Research Council. It was while working on this that he stumbled into the realm of sleep.
“I was looking at the brainwave patterns of people with different forms of dementia, but I was failing miserably at finding any difference between them,” he recalls now. One night, however, he read a scientific paper that changed everything. It described which parts of the brain were being attacked by these different types of dementia: “Some were attacking parts of the brain that had to do with controlled sleep, while other types left those sleep centres unaffected. I realised my mistake. I had been measuring the brainwave activity of my patients while they were awake, when I should have been doing so while they were asleep.” Over the next six months, Walker taught himself how to set up a sleep laboratory and, sure enough, the recordings he made in it subsequently spoke loudly of a clear difference between patients. Sleep, it seemed, could be a new early diagnostic litmus test for different subtypes of dementia.

After this, sleep became his obsession. “Only then did I ask: what is this thing called sleep, and what does it do? I was always curious, annoyingly so, but when I started to read about sleep, I would look up and hours would have gone by. No one could answer the simple question: why do we sleep? That seemed to me to be the greatest scientific mystery. I was going to attack it, and I was going to do that in two years. But I was naive. I didn’t realise that some of the greatest scientific minds had been trying to do the same thing for their entire careers. That was two decades ago, and I’m still cracking away.” After gaining his doctorate, he moved to the US. Formerly a professor of psychiatry at Harvard Medical School, he is now professor of neuroscience and psychology at the University of California.
Does his obsession extend to the bedroom? Does he take his own advice when it comes to sleep? “Yes. I give myself a non-negotiable eight-hour sleep opportunity every night, and I keep very regular hours: if there is one thing I tell people, it’s to go to bed and to wake up at the same time every day, no matter what. I take my sleep incredibly seriously because I have seen the evidence. Once you know that after just one night of only four or five hours’ sleep, your natural killer cells – the ones that attack the cancer cells that appear in your body every day – drop by 70%, or that a lack of sleep is linked to cancer of the bowel, prostate and breast, or even just that the World Health Organisation has classed any form of night-time shift work as a probable carcinogen, how could you do anything else?”
There is, however, a sting in the tale. Should his eyelids fail to close, Walker admits that he can be a touch “Woody Allen-neurotic”. When, for instance, he came to London over the summer, he found himself jet-lagged and wide awake in his hotel room at two o’clock in the morning. His problem then, as always in these situations, was that he knew too much. His brain began to race. “I thought: my orexin isn’t being turned off, the sensory gate of my thalamus is wedged open, my dorsolateral prefrontal cortex won’t shut down, and my melatonin surge won’t happen for another seven hours.” What did he do? In the end, it seems, even world experts in sleep act just like the rest of us when struck by the curse of insomnia. He turned on a light and read for a while.

Will Why We Sleep have the impact its author hopes? I’m not sure: the science bits, it must be said, require some concentration. But what I can tell you is that it had a powerful effect on me. After reading it, I was absolutely determined to go to bed earlier – a regime to which I am sticking determinedly. In a way, I was prepared for this. I first encountered Walker some months ago, when he spoke at an event at Somerset House in London, and he struck me then as both passionate and convincing (our later interview takes place via Skype from the basement of his “sleep centre”, a spot which, with its bedrooms off a long corridor, apparently resembles the ward of a private hospital). But in another way, it was unexpected. I am mostly immune to health advice. Inside my head, there is always a voice that says “just enjoy life while it lasts

The evidence Walker presents, however, is enough to send anyone early to bed. It’s no kind of choice at all. Without sleep, there is low energy and disease. With sleep, there is vitality and health. More than 20 large scale epidemiological studies all report the same clear relationship: the shorter your sleep, the shorter your life. To take just one example, adults aged 45 years or older who sleep less than six hours a night are 200% more likely to have a heart attack or stroke in their lifetime, as compared with those sleeping seven or eight hours a night (part of the reason for this has to do with blood pressure: even just one night of modest sleep reduction will speed the rate of a person’s heart, hour upon hour, and significantly increase their blood pressure).

A lack of sleep also appears to hijack the body’s effective control of blood sugar, the cells of the sleep-deprived appearing, in experiments, to become less responsive to insulin, and thus to cause a prediabetic state of hyperglycaemia. When your sleep becomes short, moreover, you are susceptible to weight gain. Among the reasons for this are the fact that inadequate sleep decreases levels of the satiety-signalling hormone, leptin, and increases levels of the hunger-signalling hormone, ghrelin. “I’m not going to say that the obesity crisis is caused by the sleep-loss epidemic alone,” says Walker. “It’s not. However, processed food and sedentary lifestyles do not adequately explain its rise. Something is missing. It’s now clear that sleep is that third ingredient.” Tiredness, of course, also affects motivation.

Sleep has a powerful effect on the immune system, which is why, when we have flu, our first instinct is to go to bed: our body is trying to sleep itself well. Reduce sleep even for a single night, and your resilience is drastically reduced. If you are tired, you are more likely to catch a cold. The well-rested also respond better to the flu vaccine. As Walker has already said, more gravely, studies show that short sleep can affect our cancer-fighting immune cells. A number of epidemiological studies have reported that night-time shift work and the disruption to circadian sleep and rhythms that it causes increase the odds of developing cancers including breast, prostate, endometrium and colon.
Getting too little sleep across the adult lifespan will significantly raise your risk of developing Alzheimer’s disease. The reasons for this are difficult to summarise, but in essence it has to do with the amyloid deposits (a toxin protein) that accumulate in the brains of those suffering from the disease, killing the surrounding cells. During deep sleep, such deposits are effectively cleaned from the brain. What occurs in an Alzheimer’s patient is a kind of vicious circle. Without sufficient sleep, these plaques build up, especially in the brain’s deep-sleep-generating regions, attacking and degrading them. The loss of deep sleep caused by this assault therefore lessens our ability to remove them from the brain at night. More amyloid, less deep sleep; less deep sleep, more amyloid, and so on. (In his book, Walker notes “unscientifically” that he has always found it curious that Margaret Thatcher and Ronald Reagan, both of whom were vocal about how little sleep they needed, both went on to develop the disease; it is, moreover, a myth that older adults need less sleep.) Away from dementia, sleep aids our ability to make new memories, and restores our capacity for learning.

And then there is sleep’s effect on mental health. When your mother told you that everything would look better in the morning, she was wise. Walker’s book includes a long section on dreams (which, says Walker, contrary to Dr Freud, cannot be analysed). Here he details the various ways in which the dream state connects to creativity. He also suggests that dreaming is a soothing balm. If we sleep to remember (see above), then we also sleep to forget. Deep sleep – the part when we begin to dream – is a therapeutic state during which we cast off the emotional charge of our experiences, making them easier to bear. Sleep, or a lack of it, also affects our mood more generally. Brain scans carried out by Walker revealed a 60% amplification in the reactivity of the amygdala – a key spot for triggering anger and rage – in those who were sleep-deprived. In children, sleeplessness has been linked to aggression and bullying; in adolescents, to suicidal thoughts. Insufficient sleep is also associated with relapse in addiction disorders. A prevailing view in psychiatry is that mental disorders cause sleep disruption. But Walker believes it is, in fact, a two-way street. Regulated sleep can improve the health of, for instance, those with bipolar disorder.

I’ve mentioned deep sleep in this (too brief) summary several times. What is it, exactly? We sleep in 90-minute cycles, and it’s only towards the end of each one of these that we go into deep sleep. Each cycle comprises two kinds of sleep. First, there is NREM sleep (non-rapid eye movement sleep); this is then followed by REM (rapid eye movement) sleep. When Walker talks about these cycles, which still have their mysteries, his voice changes. He sounds bewitched, almost dazed.

“During NREM sleep, your brain goes into this incredible synchronised pattern of rhythmic chanting,” he says. “There’s a remarkable unity across the surface of the brain, like a deep, slow mantra. Researchers were once fooled that this state was similar to a coma. But nothing could be further from the truth. Vast amounts of memory processing is going on. To produce these brainwaves, hundreds of thousands of cells all sing together, and then go silent, and on and on. Meanwhile, your body settles into this lovely low state of energy, the best blood-pressure medicine you could ever hope for. REM sleep, on the other hand, is sometimes known as paradoxical sleep, because the brain patterns are identical to when you’re awake. It’s an incredibly active brain state. Your heart and nervous system go through spurts of activity: we’re still not exactly sure why.”
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Does the 90-minute cycle mean that so-called power naps are worthless? “They can take the edge off basic sleepiness. But you need 90 minutes to get to deep sleep, and one cycle isn’t enough to do all the work. You need four or five cycles to get all the benefit.” Is it possible to have too much sleep? This is unclear. “There is no good evidence at the moment. But I do think 14 hours is too much. Too much water can kill you, and too much food, and I think ultimately the same will prove to be true for sleep.” How is it possible to tell if a person is sleep-deprived? Walker thinks we should trust our instincts. Those who would sleep on if their alarm clock was turned off are simply not getting enough. Ditto those who need caffeine in the afternoon to stay awake. “I see it all the time,” he says. “I get on a flight at 10am when people should be at peak alert, and I look around, and half of the plane has immediately fallen asleep.”

So what can the individual do? First, they should avoid pulling “all-nighters”, at their desks or on the dancefloor. After being awake for 19 hours, you’re as cognitively impaired as someone who is drunk. Second, they should start thinking about sleep as a kind of work, like going to the gym (with the key difference that it is both free and, if you’re me, enjoyable). “People use alarms to wake up,” Walker says. “So why don’t we have a bedtime alarm to tell us we’ve got half an hour, that we should start cycling down?” We should start thinking of midnight more in terms of its original meaning: as the middle of the night. Schools should consider later starts for students; such delays correlate with improved IQs. Companies should think about rewarding sleep. Productivity will rise, and motivation, creativity and even levels of honesty will be improved. Sleep can be measured using tracking devices, and some far-sighted companies in the US already give employees time off if they clock enough of it. Sleeping pills, by the way, are to be avoided. Among other things, they can have a deleterious effect on memory.

Those who are focused on so-called “clean” sleep are determined to outlaw mobiles and computers from the bedroom – and quite right, too, given the effect of LED-emitting devices on melatonin, the sleep-inducing hormone. Ultimately, though, Walker believes that technology will be sleep’s saviour. “There is going to be a revolution in the quantified self in industrial nations,” he says. “We will know everything about our bodies from one day to the next in high fidelity. That will be a seismic shift, and we will then start to develop methods by which we can amplify different components of human sleep, and do that from the bedside. Sleep will come to be seen as a preventive medicine.”

What questions does Walker still most want to answer? For a while, he is quiet. “It’s so difficult,” he says, with a sigh. “There are so many. I would still like to know where we go, psychologically and physiologically, when we dream. Dreaming is the second state of human consciousness, and we have only scratched the surface so far. But I would also like to find out when sleep emerged. I like to posit a ridiculous theory, which is: perhaps sleep did not evolve. Perhaps it was the thing from which wakefulness emerged.” He laughs. “If I could have some kind of medical Tardis and go back in time to look at that, well, I would sleep better at night.”