Disruption of Biological Rhythms- Shift Work

Shift work
1. Causes a break down in the usual coordination between internal biological clocks and external cues. This can result in an almost permanent state of desynchronisation that impairs concentration and physical performance and increases stress levels incurring long-term health risks.
2. In non-fluctuating shift work, the shift in circadian rhythm remains constant once the body adapts to it. Resynchronisation may take a while but it is possible. Fluctuating shift intensify the severity of circadian rhythm disturbance.
Research into shift work
1. Czeiler et al 1982 studied shift workers. They found high ilness rates, sleep disorders and elevated levels of stress, suggesting that the workers internal body clocks were out of sync with exogenous zeitgebers. The researchers persuaded management to move to a phase delay system of rotating shifts forward in time, to reduce negative effects. Adjusted 21 instead of 7. 9 months later appeared healthier. This shows how psychological research can lead to practical applications incuring positive outcomes.
2. Hawkings and Armstrong-Escher 1978 studied nurses working night shifts. Found that thier performance improved over a week, suggesting that the circadian rhythm adjusts gradually. However body temperature regulation was still out of sync, suggests body clock takes longer to adjust.
Evaluation of SW
1. Research suggests that disrupting biological rhythm affects cognitive process, emotional functioning and physical functioning demonstrating the severity of consequences.
2. A lot of research utilises naturalisitc field studies. These are high in ecological validity but incur many confounding varaibles, making establishment of causality problematic.
3. Much research on shift work only involved male participants which therefore means males tend to be more invovled in shift work. However, because the research is gender biased the results cannot be generalised due to the fact the results may not be representative of females.
4. Other factors- shift work effects are not just due to the disruption of biological rhythms. They may be due to the lack of sleep associated with having to go to bed at unusual times. SW expereince social disruption as well as diruption to their biological rhythms, It is difficult to meet friends and spend time with family. Soloman 1993- divorce rates may be high as 60% among all night shift workers.
5. Indivdual differences- the effects of circadian disruption vary between indivduals. It is possible that those people whose circadian rhythms change least are the ones who cope best overall. Reinberg et al 1984 found that people who gave up shift work because they could not cope tended to have rhythms that changed a lot while on shift while the 'happy shift workers' had unchanging rhythms.
  1. Evaluation resetting biological clocks- Bovin et al 1996 investigated the power of artificial light in resetting our biological clocks. 31 male subjects were divided into four groups and put onto a inverted sleep-wake cycle for three days (kept awake at night and allowed to sleep during the day). Each 'day' when they woke they were exposed to five hours of very dim light, followed by 1 of 4 conditions.: Group 1 were exposed to very bright light, group 2 to bright light, group 3 had ordinary room light and group 4 reamined in dim light. Core body temperature was used to assess each persons current circadian rhythm. After three days, members of group 1 had advanced five hours earlier; group 2 had advanced three hours; group 3 had advanced by 1 hour; and group 4 had drifted one hour later in their circadian rhythms. This shows that even room lighting can have an effect on the circadian rhythm and very bright light has a significant effect.
    1. Lab experiments- the strength of lab experiments such as Boivin et al is that extraneous variables can be carefully controlled to isolate causal variables. However, there is a question over whether the same 'laws' will apply in everyday life. It is therefore important to conduct field experiments as well to confirm the findings. Boivin and James 2002 used intermittent bright lights in a field study of nurses which confirmed the effectiveness of bright lighting to promote circadian adaption.
Real world application
1. Serious incidents like the Three Mile Nuclear Plant accident of 1979 and the Chernobyl reactor meltdown of 1986 occured due to concentration and decision failures in the early hours of the morning. This suggests that the desynchronisation effects of working at irregular hours impairs performance with potentially disastrous consequences.
Sleep deprivation- workers who have to sleep by day often expereince sleep problems because when they finish work its daytime and there are other interpruptions and daylight reduces sleep quality. Daytime sleep is usually between 1-2 hours less sleep; REM is affected (Tilley and Wilkinson 1982). Poor quality daytime sleep then makes it even more difficult for shift workers to stay awake through the night, especially when they hit the circadian 'trough'
1. Decreased alertness- Nightworkers often expereince a circadian disruption of decreased alertness during thier shifts (Boivin et al 1996). This occurs between midnight when cortisol levels are the lowest, and 4am when core body temperature is at its lowest.
  1. Effects on health- there is a significant relaltionship between shift work and organ disease. Knutsson et al 1986 found that indivduals who worked shifts for more than 15 years were 3 times more likely to develop heart disease than non-shift workers. Martino et al 2008 linked shift work to a range of organ diseases, including kidney disease. This may be due to the direct effects of desynchronisation or indirect effects such as sleep disruption.
Reducing the harmful effects
1. Rotating shifts- research indicates that most problems occur when people have to do rotating shifts, where shifts alternate every few days (Gold et al 1992). Non-fluctuating shifts are less disruptive because they can get used to the sleep-wake cycle. Although days off are likely to mean temp changes in sleeping patterns which will disrupt the biological rhythms.
2. Forward-rotating shifts- follow the logical order of the day (phase delay) and may be easier on the body and less damaging to health (according to a review by Bambra et al 2008). E.g. shift in the morning for one week, a shift in the afternoon for another week and finally a night shift in the third week.Bambra also concluded that rotating workers through shift changes more quckly (every 3-4 days instead of 1 week) is better for health and work-life balance

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