Sleep & Shift Work

People working night shifts have higher incidences of, among other things; heart attacks, depression, gastrointestinal problems and, in women, breast cancer. There is data to show that shift work can actually shorten one’s life span. Night shift workers get on average 2.5 hours less sleep when sleeping in the day than they would if they were sleeping at night.  They are less productive and more prone to accidents both at work and whilst driving to and from work. At least 75% of shift workers have been shown to be excessively sleepy during their shift.

The ‘unadjusted’ shift worker is the agent of risk, not the environment around the worker. The ‘maladjusted’ shift worker can become an agent of risk due to sleepiness as work, (resulting in missed signals e.g. a red light, a dial going critical), or through an inappropriate response to correctly perceived signals (e.g. trying to land an aircraft on the taxiway not the runway) or simply by falling asleep on the job. These issues are also pertinent to the journey to and from their place of work.

The consequences of this can be quite significant, for example manual dexterity has been shown to start to decrease from 11pm until a low point at approximately 5am and this can lead to errors or even injury. The effect of poor sleep on high level cognitive functions are even more profound in those working nights.

Many women work shifts and rotating shifts can put strain on family life, with less time available to meet family/home responsibilities and enjoy recreational and social activities. Female shift workers may suffer irregular menstrual cycles, difficulty in getting pregnant, higher rates of miscarriages, premature births and low birth-weight babies more than regular day working women.

It is not just accidents and illness that are associated with the night worker as there is date which suggests that 50% have an increase in rates of divorce as compared to day workers.

Shift work can only ever be made ‘tolerable’, it is never going to be able to be made good. Scheduling shift work needs to, as far as possible, eliminate or minimise the risk to health and safety.

Most experts agree that a forward shift rotation should be used (i.e. mornings, then evenings then nights) to minimise individual adaptation problems. However, there is an argument about the ideal length of the rotation period (the number of days on any one shift before switching to the next shift). A common shift system has a rotation period of one week, with five to seven consecutive night shifts. However, from a chronobiological view this is probably the least ideal system.

It is known to take at least seven days for adjustment of the circadian rhythms, and it is argued that just as adjustment starts to occur, it is time to rotate to the next shift.

For this reason, some researchers believe a longer shift rotation with two weeks to one month on the same shift would be beneficial as that would allow sufficient time for the circadian rhythms to adjust.

However, problems may occur if the worker reverts to a "normal" day/night schedule on their days off, thus, negating any adaptation. Others suggest a rapid shift rotation where different shifts are worked every two to three days, as it is argued that this system may reduce disruption to body rhythms because the readjustment of circadian rhythms is minimized.

Some people advocate extended work days of ten or twelve hours, this has the advantage of fewer consecutive night shifts and longer blocks of time off, however, the additional fatigue from long work hours may also have adverse effects. 

Lighting that mimics daylight can provide benefits in terms of alertness and vigilance. In many industries light levels are reduced at night making it even harder for the workers to focus on their tasks, or even stay awake.

Workers should be involved in the development of rosters as a key part of risk control, as schedules and workloads will impact on individuals differently. It is important to make sure that this input is candid, so confidential surveys, anonymous feedback or risk-free focus groups are a crucial mechanism to gain valuable information as regards to what really happens in an organisation in the middle of the night.

For employees it is important that they find a job that suits their own individual physiology in terms of morning/eveningness. Early morning types would be unwise to take a job that forces them to stay up late, owls shouldn’t become milkman. Because some people may be more suited scheduling at specific periods in a shift cycle, it would be beneficial to measure an employee’s morningness/eveningness and where possible assign them the hours that are in harmony with their chronotype. These characteristics may not be as important as broader work/life balance issues but reinforces the need for active staff involvement in work scheduling.

It is also important to remember that our ability to work shifts changes as we get older, in your twenties and thirties you may adapt relatively easily to rotating shifts while this may become increasingly problematic in your forties.

Many shift workers rely on caffeinated beverages to stay awake during the night but this could actually be making matters worse if the caffeine subsequently disturbs their sleep. They should avoid caffeinated beverages at least 5 hours before their intended bed time. The use of caffeine in workers doing the evening shift is also problematical as they will be going to sleep just a few hours after their shift finishes and the short-term benefits of the caffeine improving alertness will be more than offset by poorer subsequent sleep

Shift workers should also avoid the use of alcohol to ‘help them get to sleep’ as getting to sleep is usually not the problem, it is getting good quality sleep and staying asleep that is the issue in night workers and alcohol is going to make the problem worse.

It is an unfortunate truism that society places less value on protecting the day sleep of night workers than it does protecting the night sleep of the majority, it is impossible to make society care about your sleep but you can get you family and friends to respect your daily sleep opportunity.

Shifts should be structured with strategically placed rest and meal breaks. Shift workers should avoid the situation in which long, unbroken periods of work stretch in front of them, particularly in the early morning when alertness and vigilance are at their lowest. Ideally it should be possible for them to take short breaks every couple of hours; to walk around, get something to eat and drink or visit the bathroom.

Unless the shift worker is on a rapidly rotating shift patter it is probably best for them to avoid napping during the ‘lunch break’ of a night shift 1) because it will confuse the circadian system in believing that it is still OK to sleep at night and 2) they will probably experience sleep inertia, that feeling of grogginess that people feel after being awoken from a short sleep. Studies have found that sleep inertia is particularly severe at 4am, so a nap at this time may actually reduce safety.

A simple rule for shift work is that a correctly set body clock is the single most important factor in ensuring good sleep and fewer negative effects. Thus, within the limits of what is possible given their work and domestic routines, shift workers should be highly regular in their sleeping patterns and should consciously avoid ‘snacking’ on sleep whereby they grab it wherever and whenever they can. The process of taking naps should only be regarded as an emergency catching-up process, coping with acute sleep decrements as they occur, rather than as an integral part of the shift worker’s overall sleep strategy. The only exception to this might be an afternoon or evening nap before the first night shift.

If you work shifts, particularly night shifts, try to use public transport, if at all possible. Driving home after working a night shift significantly increases your risk of an accident.


Circadian Rhythm Disorders are a result of irregularities in the biological clock. Common manifestations of such disorders are where the biological clock has been affected by a change in sleep/wake patterns such as would be the result of shift work or trans-meridian flights i.e. jet lag. However, there are cases where the biological clock is running at a different time to normal -

There are two main forms –

  • Advanced Sleep Phase Syndrome (ASPS), where the sufferer’s bedtime has got progressively earlier in the evening so they can’t stay awake in the evening and wake very early in the morning.

  • Delayed Sleep Phase Syndrome (DSPS) is the opposite where bedtime becomes progressively later, the sufferer stays awake long into the night and cannot get out of bed in the morning.

The main symptoms are insomnia and/or excessive daytime sleepiness. Both ASPS and DSPS can be improved by trying to gradually reschedule sleep patterns until they become more ‘normal’. Exposure to bright light, either the sun or a light-box, in the morning can help a DSPS sufferer to sleep earlier and exposure to bright light in the evening can help an ASPS sufferer to stay up later.