The Hazards of Shift Work

Changes in the workplace such as job sharing, part-time work and more flexible work hours are indicators that shiftwork is on the increase. Industries such as airlines, hospitals and railways have long had round-the-clock operations and extended shopping hours are fast becoming commonplace. Research shows, however, that there can be significant health and safety issues associated with shiftwork.

The body clock
Human beings are day oriented. We are designed to work in the daytime and sleep at night.

The internal body clock (circadian clock) is responsible for this. It causes a regular variation through 24 hours in different body and mental functions. This variation is referred to as the circadian rhythm.

Body temperature, heart rate, blood pressure, respiration rate and adrenaline production, for example, normally rise during the day and fall at night. It is these changes which affect behaviour, alertness, reaction time and mental capacity of all people by varying degrees.

Nightshift
Most people find it is difficult to adapt to night work. If people rest by day and work by night, their circadian rhythms are disturbed but they never completely change to the new pattern of work and sleep. A partial adjustment may occur over successive shifts but normal circadian rhythms are usually quickly re established on days off. As well, some people are early risers who work best early in the day and slow down in the evening. Others are late to rise, slow to get going and often at their peak in the evening. Ten to 20 per cent of people who are early risers find it hardest to adjust to working at night.

Sleep cycles
Sleep disruption is the most common problem for shift workers. A sleep cycle is usually about two hours shorter after working a night shift. A decrease in sleep length also affects those who start work before 7 am. Physiologically, in the early morning hours, the body is preparing for activity which is linked to an increase in alertness. People get their longest sleep when they go to sleep before midnight and their shortest when sleep begins in the morning.

On-the-job fatigue
The level of tiredness increases with the number of hours worked and is more pronounced during the second half of a shift, especially between two and six in the morning. Another common problem experienced with sleep loss is a high level of sleepiness when awake. Many shiftworkers actually fall asleep briefly while working. These ‘microsleeps’ may last from seconds to three minutes and some shiftworkers may not be aware that they have nodded off.

Increased feelings of fatigue and sleepiness at work may make it difficult for employees to maintain concentration. This has implications for workplace safety. Judgement is impaired and response time slowed. A recent Australian study which compared the effects of alcohol and sleep loss on work performance showed that shiftworkers who have had one sleepless night can be as great a workplace hazard as someone who has been drinking alcohol.

Possible Health effects
Shiftworkers and former shiftworkers have shown more signs of ill health than people on fixed day work. Health problems may appear after a short stint of shiftwork, or may be only apparent after some years.

Common health problems often associated with shiftwork include:

• Gastro-intestinal complaints: Body rhythms for digestive function are regulated for food to be eaten during the day. The digestive system is relatively inactive at night, causing problems with some foods which are tolerated well in the daytime. Digestive complaints are often aggravated by a higher intake of caffeinated drinks consumed at night to keep awake.
• Depression and other psychiatric disturbances: These may be triggered or worsened by irregular sleep patterns and cumulative fatigue.
• Medicines for medical conditions: The effectiveness of certain medicines follows the body clock so reversal of the sleep/wake pattern can interfere with the treatment of some diseases.