Disruption to Biological Rhythms Shift work and the study by Czeisler et al

Shift Work Humans evolved to sleep at night because they couldn’t see in the dark. Shift work is a consequence of electric lights.

Starter question What are the negative effects of shift work? Write your response on a post-it note

Effects of Shift Work Problems are: Sleep deprivation Poor quality sleep Poor alertness Mistakes at Work Risk of Heart disease for night shift workers – the longer the duration of shift work the greater chance there is of CHD Job stress & emotional problems (anxiety & depression) Gordon et al.

There is now an expectation that we socialise, shop and work 24hrs a day and this can have health implications as biological rhythms will be disrupted. Cortisol levels are at their lowest at this time of night The immune system is therefore less effective and people are prone to becoming ill Shift workers have decreased alertness in the early hours of the morning.

This is why some pregnant women can suffer from morning sickness. Surgeons do not carry out operations in the early hours unless it’s an emergency as there will be an increase in infection/illness on the patient.

More frequent shift changes spell disaster! Eg fatigue, sleep disturbance, memory loss, mood swings, reduced productivity and low staff morale. Major industrial disasters, eg Chernobyl, tend to happen in the early hours, as well as fatal car accidents. Falkard reported that train divers miss warning signals on night shifts.

Key Study

The problem – 7.3 million Americans work at night, but research has shown that a complete adaption of endogenous circadian rhythms does not occur – even after years of permanent shift work. Czeisler et al (1990) believes that shift work environments that are warm and dimly lit are counter productive They believed that exposure to bright light at night and darkness during the day could help shift workers resynchronise better. Background

Aim, sample, method Aim – to evaluate if exposure to bright light at night and darkness in day can treat maladaptation due to night work. Participants – 8 men – years old. None of the participants had worked regularly on night shifts before. They had no sleep disorders. None were jet lagged within the previous 6 weeks. Method – 2 week experiment. 5 control condition and 5 treatment conditions.

1st week baseline study, 2 nd week night shift work The men lived at home but reported for ‘work’ at the laboratory each night in the second week Two men (one control, one treatment) did not conform to the protocol so their results were excluded A technician monitored the subjects to make sure they stayed awake Procedure

The control group worked during the night in ordinary indoor lights of about 150 lux The experimental group worked under bright illumination of lux, equivalent to early morning light They were also asked to stay in complete darkness from 9am to 5pm, and block all light Controls were given no specific instructions. They did use their existing window shades at times of their choosing. All completed cognitive-performance tasks hourly, but were otherwise free to do their own work. Procedure - light

Procedure - measurements The measure used was body temperature at 1 minute intervals from a disposable thermistor inserted 10cm into the rectum – Typically the circadian body temperature is at the lowest we are sleeping Approx am. So to adapt to a nightshift, the low point of body temp would have to shift to middle of the day Blood samples were collected every minutes on a randomised schedule Alertness was assessed 3 times an hour using a calculations test Subjective alertness (asking them!) Urinary excretion rates Plasma cortisol concentrations

Results Treatment study slept for 2 hours longer than control. 1.Significant shift in body temperature nadir between week 1 and 2 and between control and treatment condition. The endogenous pacemaker was adapting. 2.Behavioural changes – same behaviour but shown an hour later in treatment condition 3.Alertness and performance – the treatment conditions were more alert than the control by end of week 2.

Conclusion “Misalignment of the circadian phase and sleep deprivation are the principal factors contributing to the decrements in performance and increased accident rates associated with night-shift work. Therefore, the ability of exposure to light and darkness to adjust the circadian phase and improve the sleep of night-shift workers could have important implications for both industrial productivity and safety. Furthermore, since circadian-phase misalignment, sleep deprivation, or both may add to the deleterious consequences for health that are associated with nighttime work (such as digestive, cardiovascular, and sleep disorders), the ability to induce physiologic adaptation to such a schedule could also have important consequences for the health of night workers”.

Conclusion Or in other words: They demonstrated that maladaptation to night- shift work can be treated successfully with properly timed exposure to bright light during the night-shift work and darkness during daytime sleep.

Evaluation - weaknesses 1. Biological reductionism – this portrays the body as machine like which automatically adjusts to natural zeitgebers such as light. But there are social explanations too – There is more noise in the daytime Stress could also occur because of a loss of contact from family and friends The body may not adjust if you’re on permanent night shifts – if you want to see your family and friends at the weekend this could mean there is some permanent desynchronisation. 2. Czeisler et al claim that questions still to be answered concern: variability between individuals (age/sex), and duration and intensity of light needed for optimal adaption to night time work.

Evaluation - strengths This was a well controlled experiment that contained many different physiological measures to isolate cause and effect Overall, they showed the endogenous pacemaker is hard to shift but there are things we can do to adapt.

Clips Here’s Charles Czeisler in the flesh…. A Sleep Epidemic: Charles Czeisler at TEDxCambridge 2011 (12.39)

Other studies on shift work Boivin et al (1996) put 31 male participants on an inverted sleep pattern (so they were awake at night and slept during the day) for three days.  Each day when they woke they were sat in front of dim lights for 5 hours and then placed in one of four conditions:  1.Very bright light, 2.Bright light,3.Ordinary room light, 4. Continued dim light.  Core body temperature was recorded and used as a measure of how well they were adapting to the new rhythm. After three days:  Group 1 had advanced by five hours (they were adapting to the new pattern best)  Group 2 had advanced by three hours. Group 3 had advanced by one hour.  Group 4 had drifted backwards by one hour (were failing to show any signs of adapting).

Boivin et al (1996) Conclusions Artificial light can help us adapt our biological rhythms to suit the environment, however, brighter light is even more effective. Clearly, this useful in the workplace to help shift workers to adapt to changing sleep-wake cycles.

Activity 3 Record the aims, method, procedure, results, conclusions and evaluation in a style of your choosing: Mindmap Table Poster Keynote Flashcards etc

Exemplar paper question Some people are affected by circadian rhythm sleep disorders. Use psychological approaches, theories and relevant research to analyse circadian rhythm sleep disorders and their effects on behaviour. 20 marks

Activity 4 Read the marking instructions for this question. Create a skeleton model answer (bare bones only) using statement stems.

Have you met the success criteria? 1.3 Explain with supporting evidence, how psychological knowledge can be applied. I can explain: 1.Two circadian rhythm sleep disorders 2.Research on disruption to circadian rhythms