People may suffer disruption to their biological rhythms for a number of different reasons. For example people may suffer sleep disruption due to things such as shift work and jet lag. Many industries require shift work to keep going 24 hours a day. Examples of such industries include airline crew, doctors and paramedics. People who work the night shift are required to be alert and night and so much therefor sleep through the day. This is a reverse of their natural body rhythms and goes against most available zeitgeber cues.
Boivin et al (1996) found that night workers often experience a circadian trough of decreased alertness during their shifts� This is between the hours of midnight, when cortisol levels are at their lowest, and 4am, when core body temperature is at its lowest. This leads to the assumption that this is the period of time, during a night shift, in which most accidents may occur. A real world example that supports this assumption is the Chernobyl disaster. The Chernobyl disaster was a nuclear accident, purely down to human error, that occurred on 26 April 1986 at 3am, and therefor was during the circadian trough.
Studies of sleep, such as the one by Boivin, may result in industries re-evaluating the shifts and shift patterns that their employees work. Research has also found that shift work may also have effects of health, there was found to be a significant link between shift work and organ disease. Kuttsson et al (1986) found individuals who worked shifts for more than 15 years were 3x more likely to develop heart disease than non-shift workers. Research by Gold et al (1992) indicated that more problems occur when people have to do shifts that rotate every few days.
Czeister at al� study supports this. In this study they looked at improving productivity in a power plant. He gave the workers 3 shifts 12am-8am, 4pm-12am and 8am-4pm. He divided participants into 3 groups, one control group who had no shift changes, group A which spent one week doing the same shift then rotated clockwise (phase delay) and group B who spent one week doing each shift then rotated anti clockwise (phase advance). Results found that the control group was 20% happier, group A were 85% happier and group B were 50% happier.
This shows that rotating shifts clockwise improved the happiness of the workers. This study has had many real world applications as it has changed the shifts that many industries give their workers. This study is credible as it contains high mundane realism. People may also suffer sleep deprivation due to jet lag. The term jet lag is used to refer to the physiological effects of disrupted circadian rhythms. Jet lag occurs when travelling through different time zones and symptoms include things like; loss of appetite, nausea, fatigue, mild depression and insomnia.
Many studies of jet have been conducted on American major league baseball teams who have to travel across time zones to play major league games. Racht et al (1995) analysed US baseball results over a 3 year period. They found that teams that travelled east to west (phase delay) won 44% of their games, whereas teams that travelled west to eat (phase advance) only won 37% of games. However some people critisied this study due to the fact that the different between the games won by the teams travelling east to west and the teams travelling west to east was not significant.
They could argue that the differences may be due to other factors such as the teams travelling east to west actually having greater ability. It can be argued that jet lag can also be affected by factors other than the disruption of biological rhythms. It is possible that an individual may sleep badly the night before travelling due to worrying about the flight. Also travelling and holidays themselves can be tiring. Drinking coffee/alcohol, constant noise and low oxygen cabin air can also be cumulative factors.
This shows that the effects of jet lag may be due to a number of different factors, not just the disruption bodily rhythms. Melatonin has been put forward as a cure for jet lag/shift work. This seems logical as melatonin is the natural hormone that induces sleep. Herxheimer and Petrie (2001) studied melatonin as a cure for disruption. They review 10 studies and found that when melatonin was taken close to regular bed time it was remarkably effective. However they also found that if it was taken at the wrong time then it often hindered adaptation. This shows that melatonin may be a successful treatment if taken correctly.