Health Effects related to shift work

There are thousands of publications on shift work and possible impacts on health. The conclusions of many of the publications in the field are sometimes contradictory and / or ambiguous, and it can be difficult to use the results in practice. The reasons why it is difficult to investigate this topic are numerous, but one important factor is that people are different! Genetic differences can be very significant. Some tolerate night work without problem, while others definitely do not.

Shift work and sleep

Here you see the occurrence of insomnia among workers in different types of work schedules, from a study of 37 662 participants from the Netherlands (Boersma et al, 2023). ^{© B.E. Moen}

The most common health problem among shift workers is sleep disorders. One type of sleep disorder is insomnia; lying in bed and not being able to sleep. This is in particular a challenge for night shift workers, and is illustrated in the figure above. Also, night shift workers often sleep 1/3 less time per day than they usually do during periods of such work. Day sleep is different from night sleep both regarding length and quality. The sleep during a night can be divided in different types of sleep, for instance deep sleep and sleep with dreams; (sleep with Rapid Eye Movements” , REM). Most night shift workers have less REM sleep and less deep sleep than usual. It is possible that this may lead to the following complaints:

• Constant feeling of being tired / exhausted
• Sleep problems
• Mental irritability
• Depression

Sleep problems can be a fairly immediate reaction to shift work, and is probably the reason why many choose not to start this kind of work.

Appetite disturbance

Several studies show that disturbed indigestion and dyspepsia are common problems among people with irregular working hours. It appears that such problems develop after some time. The health problems are described both as an increased incidence of diseases such as gastritis, ulcers and irritable colon. These problems arise presumably because digestion follows the circadian rhythm although people are awake and eat at night. Also, the eating habits may become irregular when working night shifts.

Cardiovascular disease

There are studies suggesting an increased incidence of cardiovascular diseases among workers with irregular work hours. However, it is difficult to distinguish the effect of type of work and the effects of other important factors, such as smoking, for example. Smoking tobacco is a known to increase the risk of developing cardiovascular disease. It is therefore possible that the increased incidence of cardiovascular diseases within the group shift workers is related to a combination of these factors. The shift work itself may play a role, but the shift work also seems to be associated with more smoking. During the night shift, a smoker may have higher tobacco consumption than during daytime. This illustrates how difficult it is to provide reliable conclusions from studies of shift workers and for finding the cause of development of diseases. Another factor of importance is the gender; the increased risk of cardiovascular disease related to shift work is seen most clearly in men. After menopause in women (~50 years), the gender difference seems to disappear. This might indicate that hormones may be a part of the mechanism for developing this type of health problems.

Cancer

It has been shown that women who have worked night shifts for many years, are at increased risk for breast cancer. This risk seems to develop after a period of more than ten years of night shift work, and this has been found among nurses who work night shifts only, not those with other forms of shift work. This issue is debated, some find this an important issue to consider, others do not believe this information is true.

Reproduction

Some studies show that women are at increased risk for miscarriages if they work night shifts. It is most likely that this applies to women who work permanent night shifts on a regular basis, not those working in rotating shift schedules. It is not clear if this problem is related to any hormonal changes caused by the shift work, or if there are other factors on the night shifts that may cause the spontaneous abortions. Some studies also show that shift work is associated with infertility.

Injuries and accidents

There are numerous studies of shift work and accidents. Night work may increase the incidence of both injuries and accidents. This is best seen from studies in hospitals, the number of errors and mistreatment of patients increases at night. Many studies from industry show, strangely enough, that night work does not provide any increased incidence of injuries. It can be interpreted in light of the many activities that actually stop during the night, the risk of accidents and injuries is reduced. Many of these studies, however, have been conducted by the industry itself, or been paid by the industry – and one can discuss if this connection between industry and researchers may have influenced the results. Economic considerations are strong when deciding whether work should be done around the clock – or not.

Alcohol and smoking

Shift work, especially working at night and in rotation shifts, is associated with binge drinking disorder in different professions. The reasons might be be self-medication of sleep problems or coping with stress problems typical for shift work. Nurses above 50 years of age represent one important risk group for this type of alcohol use. Several studies show an increased risk of smoking among shift workers, compared to day time workers. The reasons for this habit among night shift workers are not clearly known, but it might be related to an increased stress level. However, the reason might also be that there is a special selection of workers to night shift work, and that these workers have another life style than day time workers.

Consequences for family life and social activities

Shift workers have often time off when others have not, and are sleeping or at work when others have their leisure hours. This may cause social isolation of the shift workers, and reduce the time available for family and friends. This can cause problems, which could have an impact on health. Increased incidence of mental symptoms, family problems and drug abuse has been suggested to be related to shift work.

This figure illustrates the complexity related to shift work and health. The shift work itself may cause diseases. However, in addition, the shift work may lead to behavior changes (such as increased smoking or less contact with other persons) which also can have negative health effects. Sleep disorders is a part of it all. ^{© University of Bergen}