The disruption of biological rhythms

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The disruption of biological rhythms

There has been a lot of research into what happens when biological rhythms are disrupted. This disruption can take two forms: desynchronisation, when different rhythms adapt at different rates, and flattening, when the amount of variation is decreased. Shift work and jetlag disrupt circadian and other biological rhythms; these are a source of stress as people have difficulty in making the rapid adjustments that are required, consequently there has been a considerable amount of research on both.

Shift Work

In the short term, working rotating shifts can cause sleep disturbances, fatigue, stress, irritability, errors and accidents. For example, in a hospital-based survey Gold (1992) found that nurses who worked rotating shifts were twice as likely to fall asleep while driving to work as those who worked day or evening shifts and were twice as likely to report an accident or error at work due to sleepiness.

Costa (1999) has summarised the serious long term effects of shift work. These effects include:

·         Difficulties in social and family relationships

·         The development of peptic ulcers

·         Chronic fatigue, anxiety and depression

·         Cardiovascular problems

·         Pregnancy difficulties in women


The severity of the effects varies, depending on individual factors, such as age, personality and psychological characteristics; on the working situation, such as workload schedules; and on social conditions, such as the number and age of children, housing and commuting to work.


However, it has been estimated that around 20% of all workers have to leave shift work after a short time because of serious problems.


Blakemore (1988)

Aim: To investigate possible improvements in health and productivity through changing the pattern of shift working.

Procedure: Workers in a chemical company in Utah were studied. The company operated a three shift system, in which employees worked a day shift for a week, then a night shift and then an evening shift, before starting the cycle again. The effects of lengthening the period between shift changes and rotating the shifts in the opposite direction i.e clockwise, in line with the body’s preference for a longer rather than shorter day, were assessed.

Results: Both the health and the productivity of the workers improved.

Conclusion: It is possible to modify the effects of shift work.


Conversely, a shorter shift system can also be beneficial. Williamson and


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