MODULE 7: PSYCHOSOCIAL ISSUES AND OTHER MISCELLANEOUS TOPICS IN OCCUPATIONAL AND ENVIRONMENTAL HEALTH
SECTION 7: SHIFTWORK AND HOURS OF WORK:
1. Health Effects Associated With Shiftwork

1: HEALTH EFFECTS ASSOCIATED WITH SHIFTWORK:

Factors which influence health responses to shiftwork:

Workers differ in their responses to shiftwork, and a number of factors may influence this response. Some of these are:

Age: With increasing age, sleep during the day becomes progressively more difficult. There are also some indications of slower circadian adjustment to shiftwork in middle-aged shiftworkers compared to younger ones.

Gender and Pregnancy: Although the circadian rhythms of men and women react in the same way to the phase shifting of work and sleep in connection with night work, factors such as the menstrual cycle and pregnancy result in a gender differentiated response to shiftwork. Issues such as societal accorded "gender roles" such as child care etc, have a significant impact on shiftworkers.

Physical Fitness: Some studies have shown those workers who exercised regularly reported a significant decrease in general fatigue, particularly when on the night shift, as well as a decrease in musculoskeletal symptoms and an increase in sleep length.

Flexible sleeping habits and the ability to overcome drowsiness has been shown in some studies to increase the tolerance.

Amplitude of the circadian cycle - some studies have shown that the larger the amplitude of the circadian rythym, the fewer medical problems, however, these findings are not yet conclusive.

Immediate Effects of Shiftwork:

Sleep: Shiftwork results in a periodic reduction in quantity and impairment in the quality of sleep. Night shift workers have less sleep, experience lighter and more disturbed sleep patterns. These patterns generally are not adaptive, and permanent night shift workers experience less sleep than their daytime counterparts. These poor sleep patterns contribute to overall malaise of poor feelings of well being.

A major effect of such sleep loss is the greater sleepiness during awake hours, resulting in decreased alertness or even micro-sleep episodes (falling off to sleep for microseconds). For workers in critical work positions (operating machinery, for example), this increases their risk for causing accidents.

Circadian Rhythms: The changes in endogenous circardian cycles can also result in reduced performance. During the night, these cycles result in the lowest performance and alertness. These day/night cycles may not appropriately synchronise when a worker goes onto night shift.

Social, Recreational and Family Disruption: Because of their working and sleeping times, shift workers seldom interact with normal family or social activities. For those workers with young children, such work/sleep patterns impact on child rearing (and sometimes child activities - children forced to be quite during daytime, while shiftworker is asleep), placing additional burden on the spouse. Solitary recreational activities may not be as compromised as other social activities.

Long Term Health Effects of Shiftwork:

Certain medical conditions have been associated with shiftwork, affecting particularly the gastrointestinal and the cardiovascular systems. The findings of most studies of health outcomes among shiftworks have not been conclusive, and this may be largely due to the "healthy worker effect" experienced by cross sectional studies.

Gastrointestinal System: Night work leads to a change in the sequence and timing of meals. During the night, the stomach cannot cope with the composition and the quantity of a typical daytime meal, resulting in problems of digestion. Studies have shown up to twice as many more peptic ulcers in shiftworkers, whose digestive patterns related to normal after being removed from shiftwork.

Cardiovascular Disorders: This is still an area of debate among researchers, although some Swedish studies have shown greater cardiovascular disease among shiftworkers than day workers. Prevalence of disease increased with years of work on shift. Hypothesis for this include an increase in work related stress and poor dietary habits resulting in such health outcomes.

Neurological Disorders: Studies looking at neurological or neuropsychological disorders are extremely difficult because of the variety of variables that could influence outcome, and the lack of instruments sufficiently sensitive enough to detect subtle effects. Notwithstanding this, some authors - for example, Costa (1996) - suggest that there is sufficient evidence that disorders such as anxiety and depression can be influenced by shiftwork while controlling for other individual or social factors.