Disruption of Biological Rhythms e.g. jet lag, shift work Flashcards
Explain how biological rhythms can be disrupted
Problems arise when we have to re-adjust our internal clock. If the sleep/wake cycle has to adapt to external factors it becomes desynchronised as different rhythms adapt at different rates, e.g. physiological measures (body temp, heart rate) take longer to adapt than behaviour. some rhythms (e.g. production of some hormones) are very slow to adapt. There is great individual variation in how people feel.
What are common symptoms of disruptions of biological rhythms
Tiredness, difficulty in sleeping - workers who have to sleep by day often experience sleep problems because of interruptions and daylight reducing sleep quality
Effects on health - there is a significant relationship between shift work and organ disease including heart and kidney disease and cancer.
Poor attention and concentration - shift workers often experience trough of decreased alertness between midnight and 4am where cortisol levels are at their lowest
Decreased performance - baseball teams travelling west to east (phase advance) win fewer games than those travelling east to west (phase delay)
All thse can cause serious problems, e.g. at work. Evidence for this comes from:- Chernobyl occurred between 1&4am, most lorry accidents occur between 4&7am, accidents and illnesses related to shift work are estimated to cost $77 billion annually in the USA.
Discuss what may effect these disruptions
May be differences in the work environment between day and night shift e.g. poor lighting, staffing levels may be lower, and senior manager are not likely to be present. these may partly account for the increased accidents and lower productivity of night shifts.
Also, those working shifts may have added stressors in their lives. they are likely to have reduced social activity and their work pattern may affect relationships (there is a 60% divorce rate among shift workers in the US)
Getting up or going to bed earlier than normal is phase adavnce. Going to bed or getting up later is called phase delay. Phase delay is easier to adjust to than phase advance; this may be because the body’s natural rhythm is usually about 25 hours (as shown by Siffre and others) so less adjustment is needed to lengthen than to shorten the day.
What is shift work?
This is any regular work outside hours 07.00-18.00. Long term shift work has been shown to have detrimental affects on health - workers who have done shifts for more than fifteen years were three times more likely to develop heart problems than non-shift workers. However shift work does not seem to affect everybody in the same way. Research shows that people who choose to give up shift work seem to have more disruption to their circadian rhythms than those who are relatively happy with it. Working a night shift disrupts the links between endogenous pacemakers and endogenous zeitgebers. The problems are worst at times of shift changeover. Disruption can be reduced by having a shift pattern that works with the body’s circadian rhythm.
Discuss research into the effects of shift work and how to reduce them
Czeisler and Coleman - studies workers in a chemical plant in Utah. This play used a shift pattern that went from days-nights-evenings (phase advance), changing each week. Staff had many health problems, sleep difficulties and work-related stress. Cziesler et al tried a shift patter of days-evenings-nights (phase delay) with a 3-week rotation. After nine months of the new system they found great improvement in job satisfaction expressed by the workers, productivity increased 20% and time off sick reduced markedly. Later follow-ups showed employee acceptance of this schedule after 1 year was 60%, growing to 90% after 2 years.
Czeisler - also studied the Philadelphia police department, which had a weekly days-nights-evenings pattern. Over half had sleeping difficulties and 25% had an accident during the previous year. After a year of the new 3-week days-evenings-nights pattern, accidents decreased by 40%, use of alcohol and sleeping pills dropped 50%, and there was a marked drop in sleep disturbances. These studies show that the negative effects of shift work can be reduced by shift patterns that take account of the body’s circadian rhythms:-
a) changing from days-evenings-nights is beneficial because it involves phase delay (easier to adjust to) at shift-change-over.
b) keeping to each shift for 3 weeks rather than the usual 1 week allows the rhythms to adjust
Evaluate studies of shift work
These studies are important in highlighting that the negative effects of shift work can be reduced by shift patterns that take account of the body’s circadian rhythms in two ways. Firstly, changing from days to evening to nights is beneficial because it involves phase delay (easier to adjust to) at shift-change-over. Secondly, keeping to each shift for 3 weeks rather than the usual 1 week allows the rhythms to adjust and therefore the individual is not in a constant state of de-synchronisation. These studies therefore represent a good example of how psychological research can be applied in the real work. One of the positive points about these studies is that they use real life measures such as productivity and days off sick, which are also objective. This means that these studies have ecological validity as they are applicable to the real world. However, there are a number of limitation of these studies. One important point to consider is the Hawthorn Effect. As the respondents are being studied, their work rate, productivity and attendance may improve just because they are part of the research. Furthermore, some of the results are from self-report, which tend to be inaccurate because people may exaggerate the positive effects due to demand characteristics. There are also many uncontrolled variable in this research as shift workers are affected by lots of factors other than the disruption to their biorhythms for example disruption of family and social life.
Finally, this research ignores individual differences in the response to shift work and instead just presents a general picture. Not all shift workers will be affected negatively by their working pattern, whereas some will be significantly affected.
Explain the concept of Jet lag
Jet lag only occurs when we change time zones quickly. Example: You fly from London-Boston (USA). You leave at 11am arrive 5pm British time actually it is 12 noon
Boston; by 8pm Boston time you’ll be tired as it is 1am to you normally! Klein et al - found that adjustment was faster for westbound flights (going to USA) than eastbound ones (regardless of whether you were travelling home or going away). It is easier to adapt to jet lag when flying in a westerly direction because the day of travel is lengthened (phase delay), whereas is is shortened when travelling east. Eastbound = Complete re-adjustment took 1 day per time zone crossed.
Discuss research into Jet Lag: Schwartz et al, Performance decrement.
They found that east coast US baseball teams did better when travelling West (phase delay) than west coast teams who travelled East (phase advance). The time difference was 3 hours. this would give the East coast an advantage.
Evaluation:
This is supported by Recht et al’s analysis of baseball teams over a 3 year period. teams that travelled east to west won average 44% of their games; whereas teams travelling from west to east won only 37% of their games. However, this is a study of a naturally occurring variable and teams were obviously not randomly assigned to conditions; therefore conclusions must be drawn cautiously as there may be other factors that affected performance. Also, this only measures performance decrement in baseball and other types of performance may not be affected in the same way.
Discuss research into Jet Lag: Harma et al
studied 40 female flight attendants on a 4 day flight that crossed 10 time zones (from Helsinki to Los Angeles and back). Participants rated their subjective sleepiness, measured body temperature and melatonin production, and measured cognitive performance (alertness and performance on a visual search task). This was done at two hour intervals before they flew, while they were in the USA and again after the return flight to Finland. Participants became sleepier over the 4 days, and also slept less well. body temperature and melatonin production became desynchronised from each other, body temperature re-adjusting more quickly. Sleep disturbances occurred traveling in both directions. Cognitive performance decreased. They concluded that the duration of de- and resynchornisation process of the flight attendants’ circadian rhythms is on average longer than 9 days.
Evaluation:
This study provides valuable scientific evidence for the negative impact of jet lag. It used physiological measurements of body temperature and melatonin which provide objective data. However, some of the study relied on self report, which is prone to inaccuracy, possibly more so because of sleep disturbance! This is an extreme example of jet lag - most people do not ever cross 10 time zones and back in a period of 4 days. Therefore its application is perhaps only relevant to those working in aviation. for most travellers, the effects are likely to be less extreme.
Discuss research into Jet Lag: Petrie et al
investigated the usefulness of taking melatonin to reduce jet lag in flight crew after a series of international of flights. they also investigated the optimal time for taking melatonin in a double-blind placebo-controlled trial. 52 international cabin crew were randomly assigned to three groups; early melatonin (started melatonin 3 days before arrival and carried until 5 days); and placebo. Results showed recovery from jet lag was better in the late melatonin group and worse in the early melatonin group as compared to placebo. Ratings on jet lag, energy, alertness and sleep disturbance 6 days after arrival were best for the late melatonin group and worst for the early melatonin group, with the placebo in-between.
Evaluation and real life application:
This study employed a double-blind, placebo-controlled trial to reduce demand characteristics and investigator effects, meaning it was of highly scientific nature and produced strong evidence for the value of melatonin.The findings suggest that melatonin may have potential benefits for international aircrew, but the timing is important. If taken too early, melatonin can have detrimental effects. research from animal studies backs up the claim that melatonin can be beneficial in resynchronising circadian rhythms, but there is a lack of large scale research with humans
