Work and sleep: Surviving in the 24-hour society

Shift- and nightwork are linked to reduced alertness and performance, ill health, accidents and sleep-related road crashes, according to leading experts in sleep research. Evidence presented at a major international conference at the Royal Society of Medicine (RSM), "The sleepless society: can we cope?", shows the tenacious grip our body clock exerts over work activities, with serious implications for HR and fleet managers.

Dr John Shneerson, head of the RSM sleep section, described the Selby train crash as "the most dramatic demonstration of how sleep impinges on our lives". On average, we sleep two hours a night less than our grandparents did. One worker in six works shifts. Globalisation means that the shiftwork burden is moving from blue- to white-collar staff.

The "day-within"

Dr Derk-Jan Dijk, chair of the scientific committee of the European Sleep Research Society, said: "Humans evolved on a highly periodic planet, regulated by cycles of day/night and the seasons. We are a diurnal species, we occupy the 'day' niche. The day-within is our biological clock, which generates complex physiological adaptations for us to be active during the day and asleep at night."

Sleep is accurately regulated and essential for optimal performance during waking hours. Sleep is dual-controlled, by sleep homeostasis ("maintaining a stable equilibrium") and the biological clock:

  • Our sleep homeostat keeps track of how much we sleep and how long we have been awake. With sleep loss, homeostatic processes are activated, and subsequent sleep is longer and more intense.

  • The biological clock regulates our circadian ("about a day") cycle of alternating phases for sleep and activity.

    Successful adaptation to shiftwork and the wider demands of the 24-hour society must be based on these two systems.

    We sleep longest when we sleep in rhythm. Sleep deprivation is affected by the biological time we go to sleep, as the biological clock cannot follow rapid changes in sleep times. So, when a nightshift worker goes home to rest at 9am or 10am, they may sleep well for the first two hours, but then rest becomes more and more disrupted by their biological signal.

    The biological clock and the time we are awake play a major role in alertness. Tests, such as simple addition tasks monitored over 24 hours, show that alertness is lowest during the night, until around 7am, and best during the morning and afternoon. A nightshift worker wakes in the afternoon, and is awake for several hours before working the nightshift during an unalert and potentially "dangerous" time of day.

    Trend in job performance over a 24-hour period2

    XpertHR article image

    Source: adapted from "Shiftwork: body rhythm and social factors", Simon Folkard and Joanne Hill, in Psychology at Work, ed Peter Warr, available from www.penguin.co.uk.

    Shiftwork, health and safety

    Dr Philip Tucker of Nottingham Trent University outlined the ill-health symptoms linked to shiftwork, including:

  • cardiovascular symptoms, thought to be associated with stress linked to the disruptive effects of sleeplessness; and

  • gastrointestinal disorders, linked to such factors as eating at odd times, food quality at night and stress.

    For nightworkers, Tucker's research shows a major trough in alertness around 4am, when circadian rhythms reach a low point, exacerbated by the relatively poor quality of sleep during the previous day. "Adjustment to a new shift system is slow," he suggests. Nightworkers never achieve full adjustment. On their rest days they rapidly readjust to diurnal patterns and all the adaptation work is undone.

    Overall, rapidly rotating shift systems are preferable, minimising the time spent readjusting and, for the majority of working life, ensuring a decent sleep (see box below).

    "Ideally, workers in safety-critical roles should maintain their nocturnal routines on their days off," he added.

    Night accidents

    Although studies show a marked increase in accident rates at night, several aspects of work organisation and control can mask the true comparison between day- and nightshifts:

  • the presence of additional dayworkers alongside those rotated on to daytime shifts;

  • change in work tasks, with more routine activities at night;

  • change in workloads, with lighter work at night;

  • different accident and injury reporting systems. One study showed notably fewer accidents at night, but it emerged that night staff reported accidents to the duty nightwatchman, rather than to the OH centre. As a result, less serious incidents may have been underreported; and

  • different levels of supervision between day/evening and nightwork.

    When these factors are controlled, the evidence shows that nightwork is riskier.

    Risks of early starts

    Early start dayshifts are also potentially riskier. The reason is the poorer quality of sleep the night before, with alertness levels for people starting at 6am substantially lower than for a 7am start.

    Safer shift routines

    "There's no such thing as a perfect shift system. It depends on the nature of the job," said Dr Tucker. But general safety principles include:

  • forward-rotating shift systems - morning, afternoon, night - preferable because the body finds it easier to delay the onset of sleep than to bring it forward;

  • rapid shift rotation - linked to safer working and better performance;

  • longer shifts - workers tend to prefer 12-hour shifts rather than eight, as there is less disruption to domestic and social life; and

  • accident reporting procedures - check that they are accurate, reliable and consistent across all shifts.

    Think - don't drive tired

    Professor Jim Horne of the Sleep Research Laboratory, Loughborough University, said that one crash in five on a major non-urban road is caused by sleepiness. These accidents tend to be worse because of higher impact speed. More people are killed or injured through sleepiness than alcohol.

    Sleep-related crashes tend to occur at:

  • around 2am, when people are returning home late;

  • around 4am to 6am, when people are making an early start or returning from work; and

  • mid-afternoon, when older drivers are vulnerable to sleepiness.

    When feeling sleepy, drivers should:

  • stop and take a break; and

  • drink two cups of caffeinated coffee (150mg of caffeine), followed by a 15-minute nap. The caffeine kicks in after 15 or 20 minutes. Laboratory tests show that this cuts accidents by more than 90%. Two cups are suggested because caffeine content varies widely. Energy drinks are a more reliable source of caffeine.

    More training and guidance is needed for employers and employees on the dangers of driving while sleepy, and driving at vulnerable times of the day. Professor Horne advises regular journey planning, using alternative modes of transport, and proper rest breaks. He commented on weaknesses in the Working Time Regulations1, which require rest breaks, but do not offer advice on having adequate sleep. "Rest is not equivalent to sleep," he said.

    Safety case for rapid shift rotation

    Job performance is low during much of the night, reaching its minimum at around 3am. Using injury risk rates during the morning shift as a benchmark, studies reveal:

  • An increased risk of about 10% on the afternoon shift, and just over 25% on the nightshift.

  • Over successive nightshifts, the risk becomes greater. "Risk is about 15% higher on the second night, 30% higher on the third night, and 50% higher on the fourth night than on the first night."

  • Accident rates over successive morning and dayshifts were relatively constant.

    "Systems that minimise adjustments, ie rapidly rotating shift systems, may be preferable," suggest the authors.

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    		•

    Source: "Shiftwork: body rhythm and social factors", Simon Folkard and Joanne Hill, in Psychology at Work, ed Peter Warr, available from www.penguin.co.uk .

    Shiftwork in Britain

     

    Labour Market Trends data show that, in spring 2001:

  • 3.9 million employees worked shifts most of the time in their main job, or 16% of all employees (18% of men and 13.7% of women).

  • One shiftworker in 10 works nights.

  • A two-shift system is most common (early/late or double dayshift).

  • Women are more likely than men to work evening shifts, and less likely to work "sometimes nights, sometimes days".

  • Shiftwork is most common in personal services (care assistants, home carers and nursing auxiliaries); nursing; and (for men) travel and leisure occupations.

    An IRS study found that more than half of employers (57%) operate evening, night or weekend shifts (See Working time 2000 ).

    		•

    Types of shift pattern

    Type of shiftwork

    All

    Men

    Women

    Two-shift system

    29%

    27%

    32%

    Three-shift system

    14%

    15%

    13%

    Sometimes nights, sometimes days

    12%

    14%

    10%

    Nightshifts

    10%

    9%

    10%

    Evening or twilight shifts

    5%

    4%

    7%

    Continental shifts

    4%

    7%

    1%

    Split shifts

    4%

    4%

    4%

    Mornings

    2%

    2%

    2%

    Weekends

    1%

    1%

    1%

    Other shift arrangements

    19%

    18%

    20%

    Total workers (millions)

    3.9

    2.3

    1.6

    Source: "Labour Market Trends", October 2001.

    1The Working Time Regulations 1998, IRS Employment Review 670.

    2Average (mean) performance trend.