Disruption to
Biological Rhythms
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
Background
http://www.nejm.org/doi/full/10.1056/NEJM199005033221801#t=articleTop
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.
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 – 22-29 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.
Procedure
• 1st week baseline study, 2nd 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 - light
• The control group worked during the night in ordinary
indoor lights of about 150 lux
• The experimental group worked under bright
illumination of 7000-12000 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 - 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. 04.30am. 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 15-25 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 nightshift 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)
https://youtu.be/p4UxLpoNCxU
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