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The Consequences of Disrupting Biological Rhythms. The Effects of Shift Work and Jet Lag Strategies to Minimise the effects of shift work and jet lag. BATs AO1 -Identify and describe at least two consequences of disrupting biological rhythms (jet lag and shift work)

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the consequences of disrupting biological rhythms

The Consequences of Disrupting Biological Rhythms

The Effects of Shift Work and Jet Lag

Strategies to Minimise the effects of shift work and jet lag

lessons 7 and 8 the consequences of disrupting biological rhythms

AO1 -Identify and describe at least two consequences of disrupting biological rhythms (jet lag and shift work)

AO2 - Analyse and evaluate research into the effects of jet lag and shift work on biological rhythms


Fill in the revision sheets about Bio-rhythms

Lessons 7 and 8 – The consequences of disrupting biological rhythms

Have you ever experienced any of the following:

  • Long haul flight
  • Stayed out late and then either
  • Had to get up early
  • had a long lie in?

How did it make you feel physically and mentally?


Chernobyl nuclear disaster. 25-26th April 1986. 1.42am

The causes of the accident are still described as a fateful combination of human error and imperfect technology.


The Exxon Valdez oil tanker struck Bligh Reef, off the coast of Alaska, at around 12:04 am March 24th, 1989.

The accident resulted in the discharge of approximately 11 million gallons of oil 20% of the cargo, into Prince William Sound.

The third mate failed to properly manoeuver the vessel, possibly due to fatigue and excessive workload

what do these 2 disasters have in common
What do these 2 disasters have in common?
  • Both happened in the early hours of the morning.
  • Both were thought to be caused by human error caused by disrupted biological rhythms!
  • Watch the film clip.
  • What effects can shift work have?
  • How can these be reduced?
shiftwork shift lag
Shiftwork (shift lag)
  • Can have a harmful effect on

health and well being.

  • Major cause is disruption of circadian rhythm
  • Body trying to function in complete opposite way to the instructions by Endogenous pacemakers and exogenous zeitgebers.
  • Being awake and active does not shift the circadian rhythm as daylight re-sets it
circadian trough
Circadian trough
  • Boivin et al 1996 - Night workers experience decreased alertness (at around 6am) – Circadian ‘trough’
  • Core body temperature takes even longer to re-set, which may affect performance (below optimum temperature for body functions e.g.enzymes)
  • Artificial lighting only slightly effective in re-setting rhythm
poor quality of sleep partial sleep deprivation
Poor quality of sleep, partial sleep deprivation

More difficult to sleep in day:

  • Body clock doesn’t adjust completely
  • More noise and disturbances in the day
  • Daytime sleep 1-2 hours shorter than at night
  • REM particularly affected (Tilley and Wilkinson, 1982)

Consequence is sleep deprivation – makes circadian trough worse!

effects on health
Effects on health

Knutsson (1986) – many studies show significant relationship between shiftwork and heart disease.

Those who worked shifts for over 15 years3x more likely to develop heart disease

commentary on shiftwork
Shiftwork has negative effects

Individual differences – Reinberg et al 1984

Some workers are able to cope with shifts because their rhythm changed less

Shift workers also experience social disruption – can’t spend time with friends and family

Gold et al 1992 - More problems with rotating shifts than fixed shifts (all nights)

Harmful effects can be reduced

If rotating shifts are unavoidable Phase delay (get up and go to bed later) is less disruptive than phase advance (get up and go to bed earlier)

Czeisler et al 1986 Bright lights can mimic the effect of daylight and re-set body rhythms (temp and cortisol) in 3 days (usually takes 9 days to adjust to a phase advance of 6 hours).

The strong light entrains all rhythms not just the sleep wake cycle

Commentary on Shiftwork
applying this research
Applying this research

Read ‘Reducing the harmful effects’ section on p9

Use this and what you have learned about the effects of shiftwork to write a letter or an info sheet for a new company about to employ shift workers


jet lag
Jet Lag
  • Caused by the sudden creation of a large difference between the internal clock and the external world
  • In the past travel was restricted to short distances.
  • Humans have not evolved a way of dealing with such sudden disturbances
  • Our bio-rhythms need 1 day to adjust to each time zone crossed
does the direction of travel make a difference to jet lag
East to West

Phase delay. Easier to cope with – like going to bed later

Will be ready for bed earlier, but biological clock will wake us up earlier too

West to East

Phase advance – harder – like getting up earlier

Trying to adjust to a shorter day so disruption to circadian rhythm is more pronounced

Daylight, social zeitgebers and clocks tell us it is morning when we may still be wanting to sleep

Does the direction of travel make a difference to jet lag?

Recht et al 1995 – jet lagged baseballers p8

commentary on jet lag
Commentary on Jet Lag

Sleep can be disrupted in other ways when travelling.

  • Worry about the flight/trip may cause disrupted sleep the night before a journey
  • Long trip to get to the airport before the holiday starts
  • Alcohol and coffee intake
  • Noise, uncomfortable seating, low oxygen in the cabin and annoying passengers
reducing the effects of jet lag
Reducing the effects of jet lag
  • Melatonin - ‘Miracle cure’ – Martin 2002 has found that it can help reduce jet lag if it is taken at the time of day when the traveller wishes to go to sleep.
  • Social customs and meal times – adopt the social rhythms of the destination as social cues help entrain bio-rhythms.
reducing the effects of jet lag17
Reducing the effects of Jet Lag

Stokkan et al 2001 – timing of meals can re-set the bio-clock in the liver – increases enzyme production at the right time for digestion avoiding stomach upset

Bright lights – Go out in bright daylight on first few days in a new time zone to reset body clock

explaining shift lag and jet lag
Explaining shift lag and jet lag
  • Not well adapted to abrupt shifts in day length as in nature day length changes slowly.
  • Coren (1996) – a culture shift happened at the start of the 20th century when electric lighting became widely available
  • Factories and offices could work round the clock – introducing shift work and longer working hours.
  • Social activities could also extend later into the night
  • We sleep 1.5 hrs less than 100 years

ago leading to mild sleep deprivation

explaining shift lag and jet lag19
Explaining shift lag and jet lag
  • Possible that shift/jet lag causes desynchronization of the body clocks (sleep-wake cycle and core body temperature) leading to physical distress.
  • Yamazaki et al (2000) – sleep-wake cycle can readjust in 48 hours, but other clocks e.g. temperature are slower causing desynchronization and the associated symptoms of jet/shift lag
  • Takahashi et al (2002) – melatonin speeded up resynchronization of biological rhythms after an 11 hr flight, reducing jet lag symptoms
evaluation of research on disruption of bio rhythms
Evaluation of research on disruption of bio-rhythms
  • Research findings – Consistent evidence to show that disruption can have cognitive and emotional effects on people, sometimes leading to drastic consequences,
  • but 1000’s of people do shift work without obvious effects on cognitive ability and emotional well being (so does it have real-life significance? ).
  • Methodology – Evidence often comes from field studies that have high ecological validity,
  • but confounding variables e.g. personality and individual differences in bio-rhythms are not controlled
synoptic points
Synoptic Points
  • Individual Differences – Reinberg et al 1984 – found that people who gave up shift work because they couldn’t cope tended to have rhythms that changed a lot, but ‘happy shift workers’ had unchanging rhythms
synoptic points22
Synoptic Points
  • Methodology
  • Lab experiments – Boivin et al 1996 (see p9) – effect of light on resetting biological clock
  • Good because extraneous variables controlled, but low in mundane realism
  • Field expt done (Boivin and James 2002) with nurses using intermittent bright lights. Findings also showed that bright light can reset bio-clock
  • This helps to strengthen the previous research.
synoptic points23
Synoptic Points
  • Reductionism
  • Other factors as well as biological clock disruption must be taken into consideration
  • E.g shift workers being disturbed in the day
  • Disrupted social life/social support can make people cope with stress less well (think back to the stress topic – emotion focused coping) Solomon 1993
  • Fear of flying, hassle of waiting in airports, caffeine/alcohol intake, discomfort e.t.c may disrupt sleep
over to you
Over to you …

In other words create a plan for an essay on Disruption of Biorhythms

  • Mind map (or summarise in a way that suits you better) the following …
  • Research into the effects of shift work/jet lag)

( Knuttson et al 1986, Winter et al 2008, Recht et al 1995, Tilley and Wilkinson 1982)

  • Research into how shift/jet lag can be minimised (Boivin et al 1996 and Boivin and James 2002, Petrie 2001, , Bambra et al 2008, Gold et al 1992)
  • Synoptic points – Individual Differences, Methodology, Reductionism
  • Discuss the consequences of disrupting biological rhythms.
  • (9+16 marks)
  • Look at the sample essay on p 22.
  • What grade would it get? Use the mark scheme on page vii and look at the examiners points.
  • Now write an essay that is better than the sample!!!

Use p9 qu 1-4 to help you

If you fancy more of a challenge try q 5 p9