THOMAS EDISON once commented that, ‘Everything which decreases the sum total of man’s sleep, increases the sum total of man’s capabilities. There is really no reason why men should go to bed at all.’1
Although it is true that working 24/7 provides many benefits for society – and the availability of cheap, bright artificial light has made it far easier to achieve this – Edison was wrong about this last point: chronic sleep deprivation is deadly.2 In some cases, its toxic effects may take years to reveal themselves, but it can also incapacitate us so fast and so seriously that it kills instantly.
An estimated 20 per cent of accidents on British roads are sleep-related, and these are more likely to result in death or serious injury than other types of accident, according to the British road safety charity Brake. Going just 19 hours without sleep – equivalent to waking at 7.30 a.m. and driving home from a party at 2.30 a.m. – puts your attentional abilities on a par with being over the legal drink-driving limit in England and Wales, even if you haven’t touched a drop of alcohol.3 A separate study showed that driving on four to five hours of sleep quadruples your risk of crashing, compared to drivers getting the recommended seven hours sleep.4
However, sleep deprivation winds its tentacles around pretty much every physiological process going. It affects our emotional stability, memory and our reaction speed; and our hand–eye coordination, logical reasoning and vigilance also suffer. Chronic inadequate sleep precedes the onset of Alzheimer’s disease, cancer and various psychiatric illnesses; it is also associated with heart disease, obesity and diabetes. It affects the release of both male and female reproductive hormones, and may result in reduced fertility.
In part, these risks relate to missing out on the restorative impact of sleep – simply the number of hours you notch up (or don’t) on your bedpost. However, for every one of these diseases and deficits, similar links have been made to disrupted circadian rhythms – and not only because of their effects on sleep.
In one recent study,5 researchers compared the physical effects of sleeping for five hours per night for eight days in a row with getting the same amount of sleep but at irregular times. In both groups, people’s sensitivity to the hormone insulin dropped and systemic inflammation increased, escalating the risk of developing type 2 diabetes and heart disease. However, these effects were even greater in those who were sleeping at irregular times (and whose circadian rhythms were therefore knocked out of alignment): in men, the reduction in insulin sensitivity and increase in inflammation doubled.
Some of the strongest evidence for the harmful effects of circadian disruption has come out of research on shift workers. People who work the night shift are estimated to lose between one and four hours of sleep each day, which is worrying, when you consider the responsibility carried by some shiftworkers, such as doctors, nurses and pilots. But they are also plagued by disturbances to other circadian rhythms.
While shift workers are particularly at risk, few of us manage to maintain our circadian rhythms exactly as they should be. The availability of bright light at night delays our body clocks and alters our alertness, encouraging us to stay up later, even though we must still go to work or school the next morning. As a result, many of us are waking up at a time when our bodies still think they should be sleeping, and then lying in at weekends to catch up on missed sleep, which changes our light exposure yet again. Harmless as this may seem, the ‘social jet lag’ caused by these inconsistences is akin to physically travelling across several time zones each week. It is also extremely common: studies by Till Roenneberg at the Ludwig Maximilian University in Munich, who came up with the term ‘social jet lag’, and has interrogated the sleep timings of more than 200,000 individuals from around the world, have concluded that just 13 per cent of us are social-jet-lag-free; 69 per cent of people experience at least one hour of social jet lag per week, while the remainder suffer from two or more hours.6
These are more than just numbers: another recent study found that for every hour of social jet lag people experience each week, their chances of suffering from cardiovascular disease increases by 11 per cent and they experience worse mood and greater levels of tiredness. Adding an hour of social jet lag to your week also boosts your odds of being overweight by a third.7 So, perhaps it’s no wonder that the socially jet-lagged among us are also more likely to smoke and drink heavily.
In Roenneberg’s words: ‘The more of it you experience, the fatter, dumber, grumpier and sicker you will be.’8
To understand more, and how we could find some solutions, I talked to someone who has spent almost their entire career secluded from natural light.
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Life on a submarine is stressful. The pressure from the ocean water outside is crushing. So, in order to minimise the risk of leaks, submariners must pass through several hatches before reaching the living quarters, which eats up living space. Space is further restricted by all the equipment subs carry with them: a nuclear reactor to generate energy; machines to distil drinking water and purify the air; an arsenal of torpedoes; and all the food the crew will need to survive for months beneath the waves. Submariners work in shifts, so someone is always sleeping, which means that the light in the berthing area is constantly dimmed. It’s also low in the control room so that the periscope operator can maintain night vision (it has been claimed that pirates, who often attacked at night, would wear an eye-patch to achieve the same result).
It’s small, and cramped and dark; and it smells of musty, recycled air and diesel; ‘ship smell’, as it’s known among submariners and their partners. Except for the periscope operator, the hundred-odd men who willingly cram themselves into this unforgiving environment often don’t see sunlight for months on end.
If they’re in the right part of the world and it’s safe, one of the things submariners love most is to ‘steel beach’ – to pop open the hatch, and allow the crew to go swimming, smoke cigarettes and light a barbecue on the topside of the submarine. From a commanding officer’s perspective, providing that opportunity can buy a lot with the crew: ‘They are so excited to come up, they’re like little kids,’ says Captain Seth Burton, a submarine commander in the US Navy. ‘But you have to wear your sunglasses, because you have all these submariners that have seen no sunlight – and they’re just so pale white when they come out with just their skinny little swimsuits on.’9
The usual concepts of day and night are meaningless when you’re at sea: there’s no sunlight and, because everyone is working shifts, there’s no ‘normal’ society that you’re constantly trying to slot back into. But shift work can play havoc with your sleep and health all the same.
When Burton joined the navy, US submarines operated on an 18-hour ‘day’: submariners would stand watch for six hours; spend a further six hours ‘off-watch’, which included some training and drills; and then they’d have six hours to sleep. This essentially meant that a new day came, not every 24 hours, but every 18 hours. The body is unable to adapt to such a schedule: it begins to free run on its internal close-to-24-hour rhythm, while mealtimes and sleep opportunities arrive six hours earlier day after day after day. Although there’s no sunlight, there’s the additional problem of being exposed to bright light in the mess room – often shortly before sleeping – which the SCN (the master clock) latches on to as a substitute for daylight.
Combined with the stress, and the business of living at close quarters with other men for months at a time, the constant jet lag that this schedule induces makes getting a decent night’s sleep near impossible. For the first fifteen years of his career, Burton claims that he routinely got by on four hours of sleep per day. He was constantly exhausted: ‘The Watch routines didn’t encourage the proper amount of sleep, or a consistent pattern of sleep. You were awake when you were meant to be asleep, and asleep when you were meant to be awake.’
Burton’s work schedule was extreme, but the circadian desynchrony it created is similar to that experienced by anyone who routinely fluctuates between day and night shifts or does a large amount of international travel for work. Even those with their feet planted firmly on home soil, but who regularly set an alarm clock for work and then sleep in on weekends, are likely to be experiencing some degree of circadian misalignment – a mismatch between the time in their environment, and the body’s internal time – with consequences for their health.
Although submariners are highly trained and are taught about the value of good sleep, sleep deprivation is often identified as a contributing factor when collisions and other serious incidents have occurred. ‘A very talented person might make bad decisions, just because they are exhausted,’ Burton says.
Burton blames the relentless schedule, the lack of adequate sleep and the high-stress environment for the aggressive cancer that he developed in his chest wall when he was twenty-seven years old. This has never been confirmed, but it’s plausible: mounting evidence connects circadian misalignment and shift work to cancer.
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According to European and North American surveys, 15 to 30 per cent of the working population is engaged in some form of shift work, with 19 per cent of Europeans working at least two hours between 10 p.m. and 5 a.m. In the UK, 12 per cent of the workforce – around 3.2 million people – regularly work nights – an increase of 260,000 in the past five years.
Although there may be some who enjoy working nights, for many it is a constant struggle. It’s not so bad if you consistently work the same shift and can simply pull the blinds and go to sleep as soon as the night shift is over. But many shift workers have kids to get to school in the mornings, or friends or partners they’d like to spend time with during daylight hours. Even if they don’t, just a few minutes of morning light – possibly experienced during their journey home – can counteract and postpone the ability of their internal clock to adapt to the night shift.
More than two thirds of people who work night shifts show no circadian adaptation at all, which means that they’re active when the body thinks it should be sleeping; seeing bright light when it thinks it should be dark; eating snacks and meals when the digestive system thinks it should be resting, and then attempting to sleep when the internal clock is firing off alertness signals to switch the body into daytime mode.
Irregular or rotating shifts, where people work one or two night shifts per week, are particularly difficult to adapt to. It’s not that our body clocks can’t adapt – remember that light at night delays the clock and light in the morning advances it – it’s just that it takes time. Generally, the master clock in the brain moves about an hour or two per day when adapting to a new light-dark schedule; whether this is the result of switching from day to night shifts or adapting to a new time zone. This means that, depending on the magnitude of the change, it can take several days, or even weeks, to fully adapt. Compounding the problem, the ‘peripheral’ clocks in our organs and tissues don’t adapt at the same rate – and some of them can be further disrupted by, for example, eating when the body isn’t expecting it – so not only do they fall out of synchrony with the outside world, they also fall out of synchrony with each other.
Imagine a bakery production line: to get a decent product, the individual jobs need to proceed in a fixed order. If they cease to be coordinated then, rather than a cake, you could end up with a glacé cherry crumble topped with a fried egg.
So it is with the body. Complex processes, such as the metabolism of fats or carbohydrates from the diet, require the coordination of numerous processes occurring in the gut, liver, pancreas, muscle and fatty tissue. Circadian clocks enable these organs and tissues to predict the arrival of food, so that they can process it as efficiently as possible. They also enable the chemical processes occurring inside them to proceed in the appropriate sequence, rather than all at once. If the conversation between them becomes scrambled, they become less efficient, which can lead to, for example, dangerously high amounts of glucose circulating in the blood. If sustained, this can lead to type 2 diabetes, where the pancreas no longer produces enough insulin – the hormone that allows the glucose in our blood to enter our cells and be used as fuel – and glucose levels climb even higher. Over time, the glucose can damage tissues elsewhere, such as blood vessels or nerves in the eyes and feet. In the worst cases, this can result in blindness, or amputations.
In recent decades, epidemiological studies have associated frequent shift work with some alarming health consequences. Shift workers are more likely to be overweight and suffer from type 2 diabetes. They have a higher risk of heart disease, stomach ulcers and depression. Studies of air cabin crew10 have associated regular long-haul flights with memory problems and, longer term, with significant shrinkage in brain areas associated with thinking and learning. Animal studies have shown that such brain impairments are not simply the result of sleep loss: a disrupted circadian system was causing fewer neurons to be created, and it’s this very process of ‘neurogenesis’ throughout life that is thought to support the formation of new memories.11
Another recent study12 found that a single night shift altered the circadian rhythms in chemicals produced during the breakdown of foods by the digestive system by 12 hours, suggesting that clocks in the gut, liver and pancreas had undergone a dramatic shift in their timing, even though the master clock in the brain had only shifted by about two hours. Two of these ‘metabolites’ – tryptophan and kynurenine – are commonly associated with chronic kidney disease.
Long-term shift work is also associated with the development of certain cancers – particularly breast cancer. The theoretical basis for this link was first put forward in 1987 by Richard G. Stevens, now at the University of Connecticut. Researchers had long speculated about why breast cancer is less common in low-income countries and grows more prevalent as countries industrialise. At first, Stevens and his fellow epidemiologists assumed that dietary changes were to blame, but when study after large study failed to confirm this, they drew a blank.
Stevens’s ‘Aha!’ moment came when he awoke one night and was struck by the brightness of his apartment. ‘I realised I could read a newspaper by the light coming in through the windows,’ he says. ‘Then I thought: “artificial light: that’s a hallmark of industrialisation”.’13
Various animal studies had suggested that melatonin might have anti-cancer properties. Aside from its links to the circadian system, melatonin also helps to mop up reactive oxygen species, or ‘free-radicals’, which are generated by normal metabolism and can damage DNA and other cellular components. If melatonin is suppressed because of regular exposure to bright light at night, it seems likely that more cancer-causing mutations will occur.
In fact, Stevens now believes that melatonin’s role in maintaining circadian rhythms is of greater relevance to cancer. The secretion of numerous hormones – including oestrogen, which helps to drive the growth of some types of breast cancer – fluctuates over night and day, and if melatonin is suppressed then their levels would be altered, which might enable tumours to grow more quickly. Clinical studies have indeed suggested that peak levels of melatonin are lower in women with metastatic cancer compared to healthy women, and larger tumours have also been associated with lower levels of melatonin. What’s more, totally blind women, whose melatonin secretion is unaffected by exposure to light at night, appear to have a lower incidence of breast cancer.
However, there’s more to it than just melatonin, as studies in mice that are unable to produce this hormone reveal: they develop more tumours when they are exposed to light-dark cycles that mimic shift work than do normal mice. The circadian clock controls the body’s response to DNA damage, and if these surveillance and repair systems are no longer coordinated with the times of day when DNA damage is most likely to occur, this could lead to cancer-causing mutations being missed and left unrepaired.
In the decade after Stevens first proposed a link between breast cancer and shift work, various epidemiological studies were published that seemed to support it. The first was a large study of Norwegian women, who had worked as radio and telegraph operators between the 1920s and 1980, mostly on merchant ships.14 Initially, the researchers were concerned about the impact of radio frequency radiation on their DNA; instead, they found an association between long-term shift work and breast cancer in later life.
Further support came from the Nurses’ Health Studies carried out in America, which are some of the largest investigations into the risk factors for chronic diseases in women ever to have been done. They too found an association between shift work and breast cancer – as well as colorectal and endometrial cancer – even after controlling for things like body weight, alcohol intake and exercise levels. Other studies have linked shift work to an elevated risk of cancers – particularly prostate cancer – in men. And animal studies have indicated that tumours grow faster in mice whose circadian rhythms have been disrupted.
In 2007, the International Agency for Research on Cancer classified shift work that causes circadian disruption as ‘probably carcinogenic to humans’. Their intervention came after twenty-four scientists from ten different countries reviewed the available epidemiological evidence plus the results of numerous animal and cellular studies.
Although they cautioned that it was limited, and that more research was needed – particularly to identify the most harmful types of shift work – they found the evidence for a plausible link between disrupted circadian rhythms and cancer ‘compelling’.
Two years after the IARC classification, the Danish government began offering compensation to women who had developed breast cancer and had a history of working shifts. Even so, the association between shift work and cancer remains controversial: Seth Burton will never know if those years of working 18-hour days in the dim twilight of a submarine really caused his cancer. Following his diagnosis, Burton underwent surgery and became a health nut, eating ‘a lot of wheatgrass’, and ditching meat; he also read a lot about circadian rhythms and started prioritising sleep. In June 2018, Burton marked his nineteen-year anniversary of being cancer-free.
Despite his experience, two years after the surgery, Burton went back underwater and is now a submarine commander; as he progressed up the ranks, he became more involved in discussions about the role of sleep and circadian rhythms in submariner performance. In 2013, his submarine, the USS Scranton, sea-tested a new 24-hour watch routine during a seven-and-a-half-month deployment, to investigate whether alleviating circadian misalignment might improve sleep and alertness. Among those testing the crew was Mariana Figueiro, director of the Lighting Research Center in Troy, New York: ‘Their reaction times were faster and their sleep quality better,’ she says.
According to Burton, the crew also started to look physically different: they lost weight and had better muscle tone. He suspects that this is because they were getting more sleep, and because they felt better, they exercised more. However, other research suggests that by imposing a regular routine on their mealtimes, sleep and other daily activities, this could have had other knock-on effects on their health – including weight loss.
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The sleep lab at Brigham and Women’s hospital in Boston is widely regarded as one of the top such facilities in the world. One of the first things you notice as you approach it, via a corridor from the main hospital, is that you’re walking uphill: the entire floor of the research area is thicker than the other hospital floors, and it floats separate from the rest of the building so that vibrations from everyday life don’t reach the research participants and help them decipher what time of day it is. None of the pods where the participants spend their days and nights has external windows, and to enter them you must pass through a double set of doors in order to ensure that no daylight gets in. The technicians who attend them are trained not to say ‘good morning’, or ‘good evening’, talk about the weather, or wear sunglasses on their heads – anything that might provide a clue about the time of day is banned. During longer studies (the longest so far is seventy-three days) volunteers can read newspapers, but they are given in a scrambled order, and never on the actual day they’re published. Even letters from friends and family are screened, and if necessary redacted, to ensure they give no reference to how much time has passed.
One of the problems with epidemiological studies, such as those investigating the link between shift work and cancer, is that real life gets in the way and it is impossible to control for every factor that might influence the results. But in the highly controlled environment of a sleep lab, many of those factors can be removed. One type of experiment conducted at Brigham and Women’s Hospital is the forced desynchrony protocol, which involves exposing volunteers to a 20- or 28-hour ‘day’ to deliberately decouple internal and external time and investigate the effects of this circadian misalignment on their bodies. Such studies have confirmed that disturbed sleep and decreased vigilance and mental performance are common features of circadian desynchrony – but it’s the impact on metabolic and heart function that is currently drawing the most attention.
Frank Scheer didn’t set out to become a chronobiologist, but during his undergraduate degree in biology he became fascinated by the human brain; then he encountered the brain’s master clock, and its role in regulating the sleep-wake cycle, and he was hooked. Being comprised of such a small number of cells, the SCN seemed to Scheer to be a manageable thing to study. However, the discovery of multiple clocks within the body, each generating its own rhythm, one that can be decoupled by things like food, has made Scheer’s research a vastly more complex challenge.
In 2009, Scheer set out to investigate what would happen to a hormone called leptin, which signals to our bodies that we’re full after eating, if people’s circadian rhythms became misaligned during a forced desynchrony. After just ten days, his ten previously healthy volunteers had deteriorated to the point where three of them met the diagnostic criteria for pre-diabetes. They became less sensitive to insulin, and their blood sugar levels went up; they also secreted less leptin, which left them feeling less sated after eating. What’s more, their blood pressure rose by 3 mm Hg, enough to be clinically significant in people with high blood pressure.15
His findings could help explain why Captain Burton’s men lost weight when they were able to get more sleep, and could eat, sleep and exercise at the same time each day. Sleep deprivation has also been shown to skew the balance of leptin and a second, hunger-boosting hormone called ghrelin, which helps explain why we often want to eat more when we’re tired, and tend to crave less healthy sweet, salty and starchy foods.
Mounting evidence suggests that, in terms of broader aspects of health, as well as maintaining a healthy weight, it’s not just what we eat, but when we eat it that matters. And that applies to everyone, shift worker or not.
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Gerda Pot is a nutrition researcher, investigating how day-to-day irregularity in people’s energy intake affects their long-term health. She was inspired by her grandmother, Hammy Timmerman, who was rigorous about routine. Each day she’d eat breakfast at 7 a.m.; lunch at 12.30 p.m., and dinner at 6 p.m. Even the timing of her snacks was intransigent: coffee at 11.30 a.m.; tea at 3 p.m. When Gerda came to visit, she soon learned that sleeping in was a mistake: ‘If I woke up at 10 a.m., she’d still insist I ate breakfast, and then we’d be having coffee and a cookie half an hour later,’ she says.
Increasingly, though, Gerda is convinced that Hammy’s rigid routine helped keep her in good health until she was almost ninety-five; enabling her to live independently until her final year, and even master Skype so that she could keep in touch with Gerda when she left the Netherlands and moved to London. Using data from a national survey which has tracked the health of more than 5,000 people for over seventy years, Gerda discovered that it’s not only what people eat that makes a difference, but consistency in the amount they eat at each meal:16 even though they consumed fewer calories overall, she found that people who had a more irregular meal routine had a higher risk of developing metabolic syndrome – a cluster of conditions, including high blood pressure, elevated blood sugar levels, excess fat around the waist and abnormal fat and cholesterol levels in their blood, which together increase the risk of cardiovascular disease and type 2 diabetes.
However, when we eat our meals is also important. Scientists have long noticed differences in the way we respond to food at various times of day. When overweight and obese women were put on a weight-loss diet for three months, those who consumed most of their calories at breakfast lost two and a half times more weight than those who had a light breakfast and ate most of their calories at dinner – even though they consumed the same number of calories overall.17
Many people think that the reason you gain more weight if you eat late at night is because you have less opportunity to burn off those calories, but this is simplistic. ‘People sometimes assume that our bodies shut down when asleep, but that’s not true,’ says Jonathan Johnston at the University of Surrey, who studies how our body clocks interact with food.18
The way we metabolise and process food varies across the day, which makes sense: ‘If your food is arriving at a regular time of day, you want your metabolic clocks synchronised to when you’re going to eat, so that they can process it as efficiently as possible,’ says Johnston.
One thing that varies across the day is the sensitivity of our tissues to the hormone insulin, with people becoming more resistant to its effects at night. Insulin encourages our tissues to take up glucose from the blood, so eating a large meal later in the day could lead to higher levels of circulating glucose. Over time, this might increase someone’s risk of developing metabolic syndrome and type 2 diabetes. However, that’s not the same thing as gaining more weight. If you’re eating more calories than your body uses, your tissues will eventually store some of it as fat, regardless of daily variations in insulin sensitivity.
It also seems to be the case that more energy is used to process a meal when it’s eaten in the morning, compared with later in the day, so you burn slightly more calories if you eat earlier. However, it’s still unclear how much of a difference this would make to overall body weight. For now, the take-home message is that it is probably healthier to breakfast like a king, lunch like a prince and eat dinner like a pauper – but we don’t yet entirely understand why.
So the timing of our clock influences our response to food, but it also works the other way around: Johnston has discovered that the timing of our mealtimes can also alter the timing of our clocks – but not all of our clocks. Altered mealtimes shifted some metabolic rhythms without changing the central clock in the brain.19 This indicates that mealtime can reset the clocks in human metabolic tissues – perhaps the liver, fat and muscle – which means that eating at irregular times could be another source of circadian misalignment.
Eating irregular amounts at irregular times doesn’t just affect our metabolism: the delicately balanced nature of our circadian rhythms means that disruption in one area may have unexpected consequences elsewhere. When mice were fed in the daytime, when they would usually be asleep, scientists found that they sustained more skin damage in response to UV light, compared with those fed at night. The clocks in their skin had shifted, meaning that a crucial DNA repair enzyme was now being produced at an abnormal time.20
There may be other factors, like exercise, that could decouple our clocks if timings are unexpected. Performing vigorous exercise, such as running, just before bed can interfere with your sleep because it boosts levels of adrenaline and cortisol, which increase alertness. However, animal studies suggest that exercising at unexpected times, such as when you’d usually be sleeping or preparing for sleep, also alters the timing of clocks in the muscles, lungs and liver, without altering the master clock in the brain.
The message from these studies is clear: you don’t need to be regularly flying across time zones, or working night shifts, for your internal clocks to become scrambled – and, potentially, for your health to suffer. If it’s possible to regularise your schedule – which may also mean getting to bed earlier on work nights, cutting down evening light exposure, and trying to get outside more during the daytime – it could have tangible benefits for the way you look and feel. And it may also boost your chances of living to a ripe old age, just like Hammy Timmerman.
Finding a solution to the problem of shift work is less easy. Insisting that people stop working nights is impractical; we need hospitals and power stations to work around the clock, and there are huge benefits to the economy created by both shift work and international travel. Even the sleep lab at Brigham and Women’s hospital employs a shift rota to enable its research participants to be monitored 24/7.
However, some of these discoveries about meal timings could help. One thing night-shift workers have control over is when they eat, and if they can keep regular mealtimes during the day, and try to avoid food during the night, they might avoid some of the metabolic disturbances they will be experiencing because of circadian misalignment (at least if they’re only working a couple of night shifts a week). This is something Scheer is currently testing.
Another solution to the circadian desynchrony brought about by working nights and absorbing light at the wrong time could be artificial light itself.
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Forsmark Nuclear Power station looms out of the flat forest landscape, like a young child’s Duplo model of how a building should look: the three large, grey-white blocks of Forsmark 1, 2 and 3, are each 500 metres high, and topped with straight, 400-metre chimneys. Viewed from the sea, their colour is such that on a cloudy day – as is common in central Sweden – you could easily mistake them for the sky.
Yet there was little mistaking the alarm that rang out at Forsmark on the morning of 28 April 1986. It was triggered by an employee who had accidentally left something in the control room and was going back to retrieve it. En route he passed a radiation detector, which identified high levels of radiation on his shoes, prompting fears that an accident had occurred within the plant itself. Further investigations revealed that he had, in fact, picked up the radiation outside: it had been carried some 1,100 km across the Baltic Sea, from the Ukrainian town of Chernobyl.
Many famous industrial accidents have occurred at night. The Chernobyl disaster happened at 1.30 a.m.; the alarm to the Three Mile Nuclear incident of 1979 was raised at 4 a.m., while the 1989 Exxon Valdez oil spill off the coast of Alaska occurred at midnight. All three incidents involved errors by night-shift workers, which subsequent investigations at least partly attributed to sleepiness.
Our alertness and cognitive performance vary over the 24-hour period, reaching their nadir during the early hours of the morning – at around the same time as our body temperature is at its lowest. They also start to deteriorate if we stay awake for too long, which is bad news, considering that it’s not uncommon for people working irregular shifts to go more than 20 hours without sleep, particularly during their first night shift.
The longer the night shift, and the more night shifts worked in a row, the greater the risk. Taking a nap either before or during a shift can help – although, because it can take a while to regain full alertness after sleep, this is a bad idea for jobs that demand an instant reaction to a problem. This rules out mid-shift napping for submariners, who must spring to action at a second’s notice. It is also probably unwise if you’re manning the control room at Forsmark.
Operating a nuclear power station is a monotonous job, although the managers at Forsmark try to mitigate the potential tedium through education (there are a lot of procedures to learn) and by changing workers’ roles. Each day, there is a long list of checks and tests to work through: there are 3,000 rooms in Forsmark 3 alone, some of which you can only enter if you’re wearing a radiation-proof suit, or only view through a CCTV camera. And once you get to the end of that list, it’s time to start again.
If a problem is detected, you need to be able to think on your feet. The control room operators have instructions on what to do in the event of an earthquake, a flood or an aircraft crash, but they can’t plan for every possible scenario. The accident at the Fukushima Daiichi plant in Japan – the result of a 15-metre tsunami disabling the power supply and therefore the cooling of the three nuclear reactors – is testament to that. As Jan Hallkvist, the operations manager at Forsmark 3, says: ‘People need to be alert, and able to solve complex problems quickly.’
The control room operators at Forsmark work in rotating shifts, including two night shifts per week. Maintaining alertness within the control room is made even more difficult by the fact that it’s buried deep in the heart of the power station, with metres of metal and concrete separating it from the outside world. The problem is particularly severe during the winter months. Located at roughly the same latitude as the Shetland Islands and Anchorage, Forsmark’s control room operators see barely any daylight from November to February, regardless of which shift they’re working.
As if to compensate for the lack of windows, four paintings depicting the changing seasons have been hung above the entrance to the meeting rooms. But otherwise the control room is a drab, beige kind of place, lined with giant circuit boards that map out the reactors’ connections to the grid and show how much power is being generated at any given time.
I’d liken it to a cave, but Hallkvist does it for me: ‘We had to do something about the lighting,’ he says, walking over to a control panel on the wall.
Hallkvist originally approached the circadian researcher Arne Lowden about his workers’ shifts. He was looking for ways to help his staff adjust to their changing schedules and maintain their alertness, but he also mentioned the gloomy control room. Lowden told him: ‘If you’re going to change the lighting, you should think about circadian lighting.’
Although the high blue-light content of standard LEDs disrupts circadian rhythms when people are exposed to them at night, LEDs also enable at least some of the effects of daylight to be realistically recreated indoors. Because they are tiny, many different-coloured LEDs can be joined together to vary the shade of the light they produce, enabling the colour and intensity of a lighting system to be adjusted according to the time of day.
For an extra couple of thousand euros, Lowden explained, it would be possible to install a ‘circadian lighting system’ that could supply a shot of intense white-blue light to boost workers’ alertness at key times, such as the start of a night shift, but also fade to a dimmer, warmer white in the run-up to the shift’s end, preparing them for sleep – in this way, the night shift would be more like an afternoon/evening shift, and when the workers got home they would be ready to sleep. Similarly, the intense, blue-white lighting could provide a substitute for sunlight for those working day shifts in the cave-like interior of the control room, keeping them rooted in the 24-hour world.
Hallkvist was intrigued enough to allow Lowden to test whether such lighting could really boost alertness and sleep in a subset of his workers, as well as help them better adapt to rotating shift work. Beforehand, the illuminance in the control room was a weak yellow light of 200 lux – like that of many offices. The new lights were hung above the reactor operators’ desk and, at their peak, yielded 745 lux of intense blueish-white. The rest of the operators worked at desks turned away from the new lights so that they could function as controls.
The experiment was performed during winter, and the results21 were positive enough to persuade Hallkvist to install the lighting system throughout the control room. The most convincing result was a reduction in the reactor operators’ sleepiness during both night and day shifts – but particularly during the second night shift, which is often the hardest. This was despite the reactor operators being exposed to the intense white-blue light for only one to two hours at the start of the night shifts. During day shifts the bright lights were on between 8 a.m. and 4 p.m. – replicating what was occurring in the outside world.
Even so, not everyone is convinced about the wisdom of exposing night-shift workers to intense white-blue light. It boosts their alertness, but it’s also suppressing their release of melatonin and delaying the timing of their clocks. ‘It’s not an easy fix,’ says Scheer. ‘There’s a risk of making things worse by interfering with light exposure during or after the night shift.’ He points to the example of blue-blocking glasses, which some tout as a means of shielding oneself from daylight on the journey home: it’s true that this may make it easier to sleep, but if you’re driving, it also increases the risk of accidents.