Disruption of biological rhythms

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shift work and shift lag

  • Decreased allertness- Circadian troughs are often experiencend by night workers between 12am and 4am. These occur due to body temperature and cortisol levles being at their lowest.
  • Sleep deprivation- people who work shifts are often sleep deprived. Sleeping during the day is tough due to daylight and noises outside and on average poeple that sleep in the day have 1-2 hours less sleep than normal. REM sleep is particularily affected (Tilley and Wilson 1982) and the poor quality of sleep makes it even harder to stay awake at night.
  • Effect on health- There has been research to support that people who work shifts suffer more from organ disease. Knutsson et al (1996) fround that individuals who worked shifts for 15+ years are 3 times more likely to suffer from heart disease than non-shift workers.
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Jet travel and jet lag

Why do we suffer from disrupted circadian rhythms?

Thought that the dorsal position of the SCN takes seeral cycles to fully resynchronise to abrupt changes. Winter et al (2008) calcualted  that its is a day per hour of change, to recover. 

Symptoms of jet lag:

  • Loss of appetite 
  • Nausea 
  • Fatigue
  • Disorentaion 
  • Insomnia
  • Mild depression

Baseball team

West coast is 3 hours behind the east. when east teams go west they experience a phase delay and they won 44% of games however west to east this dropped to 37%. 

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Phase delay and phase advance

Phase delay (East to west) is better 

 (http://www.myhousecallmd.com/wp-content/uploads/2010/02/jetlag-725811.jpg)Phase Advance (West the east)is worse

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Other factors

Shift work effects

Social disruption, devorce rates as high as 60% amoung all night shift workers (Solomon 1993)

Other factors influencing jet lag

  • Disrupted sleep the night before
  • Drinking alcohol or coffee
  • Constant noise
  • Low levels of oxygen 
  • Annoying passengers


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Reducing harmful effects

Rotating shifts

Research has shown that rotating shifts may cause most problems, where they alternate every few days (Gold et al 1992). Non-fluctuating patterns better so the individual can settle into a pattern.

Forward-rotating shifts

Bambra et al (2008) suggested that following the logical order of the day may be easier  (phase delay) 

Atrifical lighting

Can be used to re-set the rhythms (Bovin et al 1996, 31 male PPs, Kept awake at night and slept thruough day. When awake, 5 hours of dim light followed by either very bright, bright, ordinary or dim light. After 3 days the v.bright had advanced 5 hours, bright was 3, ordinary was 1 and dim was a delay of 1.) 

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Reducing harmful effects continued...


Can be taken before bed to help sleep and has been found effective, however if tken at wrong time can have negative effects.

Social customs

Eating at certain times can hep to entrain the biological rhythms (Fuller et al 2008). so helps to fast and then eat at the times when the clock says you should has shown to help.

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Knowing how jet lag and shift lag can effect us is important in understandinf how to reduce effects. If we can sucessfully do this then we may be able to avoid disasters such as chernobyl (1986).

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