April 5, 2009

During the course of evolution, humans have evolved internal physiological and behavioural mechanisms that are closely linked to the time in their environment. It is believed that pairing an organism’s behaviour and physiological reactions to their environment increases their chance of surviving by ensuring that they are active at times of the day that are beneficial to them. Modern society, however, has thrown our evolutionary adaptation out of balance. Our present society requires that a portion of the population is awake at all times of the day. Power generating facilities need employees to monitor electricity generation, doctors and emergency workers must be available and factory workers ensure that a maximum level of production is reached. Nevertheless, living in a 24 hour society has consequences, especially for shift workers. Apart from higher rates of accidents, shift workers are prone to suffer from a variety of health problems including: sleep disorders, gastrointestinal disorders, cardiovascular health problems, lipid intolerance and a higher risk of developing diabetes.

This leads us to the following questions: why are shift workers more prone to health problems than non-shift workers? Can these workers simply make up the sleep they have lost at night during the day? The answer lies within a phenomenon known as circadian rhythms. Circadian rhythms are the daily variations in physiology and behaviour that occur within every organism. Circadian rhythms are maintained by a master biological clock, known as the suprachiasmatic nucleus (SCN). The periodicity of the clock is determined genetically and reflects the natural wake/sleep cycle. Circadian rhythms therefore require that behavioural and physiological phases in the body are aligned to obtain proper sleep. Sleeping at times when the phases of the circadian cycle are not aligned (for example, when body temperature is rising and melatonin levels are falling) will result in poor sleep quality. As such, shift workers who are attempting to sleep during the day after a night of work may have difficulty sleeping due to the fact that the phases of their circadian rhythm are no longer synchronized. Circadian rhythms can adjust over time, but the process is lengthy and workers may have been assigned to a different work shift by the time their circadian rhythm re-synchronizes. In addition, light and exercise can shift circadian rhythms, and hence, it may be difficult for workers to sleep well if they are exposed to light (even dim light) during the day.

In itself, poor sleep or sleep deprivation can have dire consequences. Lack of sleep often results in errors, slower reaction times, decreased vigilance, impaired memory and reduced motivation. Results for task performance after 17-19 hours of sustained wakefulness are similar to those obtained with individuals who have a blood alcohol level of 0.05%. 20-25 hours of sustained wakefulness will produce similar results to those obtained with individuals with a blood alcohol level of 0.1%. This is above the legal limit for alcohol. The maximum amount of hours that a hospital intern is allowed to work is currently 24 hours. This is nonetheless dangerous considering the effects of sleep deprivation following such a long work period. Sleep deprivation has been linked to many documented medical errors.  Although controls have been established to regulate hours of work, present legislation often fails to recognize the effects of sleep deprivation on mental alterness and performance. Perhaps it is time to review our current regulations to ensure that our workers are safe.   

The information for this article was obtained from:

Rajaratnam, Shantha MW, J. Arendt. 2001. Health in a 24-h society. Lancet. 358: 999-1005