Despite the lack of a legal definition, different types of shift work have some common characteristics. These include work during the afternoon, night or weekend, with periods of the work scheduled outside daytime hours; extended work periods of longer than twelve hours often associated with a compressed working week; rotating hours; split shifts; overtime and standby or on-call duties. Within these are other features: shift pattern (permanent or rotating, forward and backward), shift rotation (fast or slow), shift timing, shift duration, and rest breaks between shifts.
Shift work is prevalent across a range of industries, however the variety in working patterns makes it difficult to determine how challenging it is. Assessment will consider many factors such as how long the employee has been awake for, how long the shift has been, how many breaks taken were taken, whether the breaks were paid or not, and so on.
According to the European Working Conditions Survey, 22% of UK employees work shifts, while 22% of UK employees report having worked at least one night-shift a month. The Trades Union Congress (TUC) estimated that there were 3.2m night workers in the UK in 2017 (equivalent to 11.7% of the working age population).
Shift work prevalence varies by country. Within the EU for example it can reach 40% of the population (Croatia). In the US in 2010 according to the National Health Interview Survey, 29% of workers work hours outside 6.00a.m and 6.00pm.
Shift work prevalence also varies by profession. Survey data of the nursing workforce collected by the Royal College of Nursing (pdf) showed that 57% worked shifts, with 10% working permanent nights and 58% on rotating shifts.
It should be noted that precise figures of shift work prevalence are hard to come by, as estimates vary depending on how shift work is defined (by different sectors and between countries). However, it is unlikely that these figures will go down, which is why gaining insight into the health consequences of shift work is important.
Image: Tim Vrtiska
Cardiovascular Disease – 34 observational studies of over two million people, suggest that shift work is associated with increased risk of myocardial infarction (pooled risk ratio 1.23) and ischaemic stroke (pooled risk ratio of 1.05). The highest risk is associated with night shifts (risk ratio 1.41). There is no significant risk from evening shifts.
Metabolic Disorders – Shift work is associated with obesity and weight gain (with one estimate of risk ratio at 1.14), and impaired glucose tolerance. For type 2 diabetes data from cohort studies puts the risk ratio between 1.12 and 1.15. These are not large effects but are significant.
Cancer – In 2007 The International Agency for Research on Cancer stated that shift work probably increases the risk of breast cancer. Since 2007, three other reviews have concluded that there is insufficient or limited evidence. Four reviews have reported that long exposure to shifts (>20 years) is associated with elevated risk for breast cancer with risk ratios ranging from 1.06 to 1.20. For prostate cancer, a meta-analysis based on eight studies found that the risk ratio is 1.24, with a 2.8% increase in risk for each five year’s duration of night shift work. For colorectal cancer the available evidence paints a similar picture: a meta-analysis of six studies reported an odds ratio of 1.32, with an 11% increase in risk for every five years of night shift work.
Today, research is being conducted on several other areas of interest centred on other consequences including life expectancy, cognitive decline, depression, multiple sclerosis and overall quality of life. Other research looks at individual differences and how sex, age, and chronotype (whether one is a morning or evening person) can affect the risk of negative outcomes.
Effects on genes and other processes – The effects of mistimed sleep (through shift work or jet lag for example) on peripheral circadian rhythm disruption have also been characterised at the molecular level, as seen in gene expression studies. Genes and processes at the core of circadian rhythm generation and gene expression were reduced significantly, although the centrally driven circadian rhythm of melatonin is not affected. Research at the molecular level adds important insights to the overall biology of sleep and the effects of sleep disruption.
- Educating and informing people about health in relation to shift work, such as educating shift workers about good sleep routines, including how to compensate for lost sleep and how to get back into day-mode after shift work at night. Research in a cohort of London junior doctors showed that 76% found education alone improved outcomes either by improving their core sleep, how they worked at night, or both. This is an intervention that really brings into focus the impact of messaging. Mike thinks that promoting the idea of coping with shifts is unhelpful and we should not expect people to perform to super-human standards. At the end of the day, shift workers are not super-human but have the same physiology as everybody else.
- Creating appropriate shift schedules: while these will differ for different people in different situations, it should be acknowledged that workers need a higher degree of control of individual working patterns. Intelligent rostering software can take individual preferences into account.
- Considering lighting: lighting is a powerful tool that can modulate shift work consequences.
- Promoting rest and breaks: there is currently a wide range of what we think is acceptable in terms of break timings and durations but there are likely to be benefits from a more considered approach. For example, there might be different break periods needed between professions, for example between heavy goods vehicle (HGV) drivers and medical consultants.
- Provision of facilities: it is especially important to have access to high quality food, including the ability to take a proper break in a well-designed space with adequate rest facilities. This type of space is provided for flight crew by some airlines.
- Proactive screening: since shift work is likely to cause sleep disruption, and as a consequence a range of resulting health outcomes, access to at least annual health checks is important.
- Challenging misconceptions: communication is key in many public health interventions. Changing the language around shift work and endurance, moving away from referring to shift workers as ‘superheroes’ for working at night or not taking breaks, can take some pressure off shift work.
- Medication: Using medication should not be routine unless absolutely necessary (for example the use of drugs such as modafinil to stimulate attention). While there may be a role for some medications, such as melatonin, this decision should be made after consulting with a trained healthcare professional. Interventions should assess the overall health and specific circumstances of a person. Medications should not be used as a blanket approach to managing shift work.
- Preventing driving when tired: driving home after night shifts can lead to accidents that can be lethal. It should be the responsibility of employers to ensure that their staff can get home safely. Junior doctors now benefit from being given a bed to sleep in at work, if they are too tired to drive home and every employer should be considering ways to manage similar risks in their sector.
For example, let's take the sector's system determining pilots’ fitness to fly, which takes tiredness into account. Pilots’ working hours are controlled through European regulation (and deregulation) which comprise two main components:
- The prescriptive rule-set which is a complex set of rules defining quantitatively what is allowed: for example, a maximum of 900 hours per year. This rule-set can “allow” very fatiguing rosters to be created.
- An overarching rule-set that pilots must not fly when “too fatigued” and airlines must not roster pilots to do fatiguing duties.
These systems create a catch 22 situation: pilots need to carry out a number of tasks that make them tired, but are not permitted to carry out these tasks if they're "too tired". But how tired is too tired? There is an exemption from the prescriptive rule set to allow bespoke assessments of the risk, through so called Fatigue Risk Management Systems (FRMS), but these are vulnerable to conflicting interests. Adding to the complexity of this assessment system, pilots report finding it less tiring to put up with something rather than to go through the process of reporting instances of where fatigue has been an issue.
For example, pilots can decline work due to fatigue. But there are precedents of airlines contesting pilots' assessments and subjecting pilots to disciplinary action. In one such case, data on effectiveness showed that the pilot’s level of fatigue on the declined day of duty was equivalent to being four times the legal limit for drinking alcohol.
Along similar lines, a body of research from 2003 investigated crew sleep patterns in the cockpit on transatlantic flights. Figures showed periods of alertness and sleep in both the captain and the first officer. The captain’s scheduled nap provides rest to allow them to be well rested for landing at GMT 11.30. Despite this, both pilots were flying through the circadian load and there were several instances where neither pilot was fully alert.
The question then arises as to how aviation is so safe, given the commonplace experience of fatigue on the flight deck? Let's look at this video describing a recent near miss in 2017 as an Air Canada plane began to land on a runway where four other full passenger aircraft were taxiing for take-off. The Air Canada plane came within 13 feet of the other aircraft. The subsequent investigation found that the captain of the Air Canada flight had been awake continuously for 19 hours. A crash was averted through a set of established safety procedures instigated by air traffic control and auto-pilot safety functions in the aircraft, and to some degree, luck.
Shift work is a risk factor for poor quality sleep, particularly for those working nights. Crossrail and Transport for London research sought to examine the impact of shift work and the impact of changes to shift patterns. They examined a number of interventions that modulated shift duration and frequency. They found that people who worked shifts shorter than ten hours did not necessarily have better sleep, probably because they had more leisure time and were not prioritising sleep. This motivated a key Crossrail policy that staff “arrive at work fit and ready to work”, including not being ill, not on medication and not sleepy. Still, managing human resources in such a setting is challenging as certain policies could be argued to blur the boundaries between professional and personal life.
In summary the Crossrail working hours policy requires:
- An uninterrupted break of one day in seven days, or two days in a 14-day period
- A minimum rest break of 20 minutes when working more than six hours and two breaks if working twelve hours
- No more than twelve hours per day shift, 14 hours door to door
- No more than ten hours per night shift or early shift
- First night shift no more than eight hours
- A minimum of twelve hours rest between shifts, or 14 hours for consecutive nights
- Not to work more than 60 hours in any seven day period
- An uninterrupted break of one day in seven days, or two days in a 14 day period
- Overtime not to exceed by two hours past usual shift
Taking all the research and contextual factors into account led to Crossrail’s Fatigue Management Plan:
- Identify all staff who work some form of shift roster patterns
- Apply the HSE Index, if the pattern falls outside, re-evaluate
- Carry out occupational health assessments for all on night shifts
- Provide information and training for those ‘at risk’ to better understand lifestyle issues
- Review fatigue after a month, and every three months
- Include fatigue into accident investigation. If it's a root cause, further review
- Undertake a management review each year