used to refer to the physiological effects of disrupted circadian rhythms.
Our biological rhythms are not equipped to cope with sudden and large
changes; it is estimated that the dorsal portion of the SCN takes several
cycles to fully resynchronise to abrupt large changes in environmental
time- a process we experience as jet lag. Winter et al 2002 calculated that
this is equivalent to one day to adjust to each hour of time change.
Symptoms include loss of appetite, nausea, fatigue, mild depression and
insomnia.
The symptoms are thought to be
caused by melatonin release being out
of step with the new environmental
conditions. Evidence suggests that
melatonin supplement pills taken in the
evening may reduce the effect of jet lag
(Blackmore 1988)
Caused by travelling across time zones so quickly that
biological rhythms do not match external cues,
causing sleepiness during the day and restlessness
during the night. This lasts until resynchronisation has
occurred, it can take up to a week to fully synchronise
to a new time zone.
Wegman et al found that travelling east to west (phase delay)
seems easier to adapt to tan travelling west to east (phase
advance). This is supported by Klein et al 1972 who tested 8
participants flying between the USA and Germany, and found
that adjustments to jet lag was easier or people on Westbound
flights than eastbound, regardless of whether they were on an
outbound r homebound flight, supporting the fact that phase
advance has more severe consequences.
Perfrmance decrement
Schwartz et al 1995 found that
baseball sides from the eastern
USA play better against teams in
the west than western sides did
playing againt teams in the east.
This supports the ide that phase
advance has more severe
consequences. However, it may
just mean that eastern teams are
superior.
Dealing with the conseqeunces
Webb and Agnew 1971 found that
successful strategies for coping with jet
lag includes outdoor pursuits, expose to
light ad regular mealtimes. This
suggests that following exogenous
zeitgebers is the best way to address
the consequences of jet lag. However,
there are indvdual differences; some
people are more resistant to the effects
of jet lag than others. This is known as
phase tolerance.
Evaluation
Melatonin has been put forward as a
miracle cure for jet lag and shift work.
Because it is the natural hormone that
induces sleep. Petrie et al 2001
reviewed 10 studies and found that
where melatonin was taken near to
bedtime, it was effective. However, if
taken at the wrong time of the day if may
actually delay adaption.
Social customs- this can help to entrain
biological rhythms. E.g. when travelling,
it helps to eat at the right time and go to
sleep when the clock says it is time to go
to sleep. Recent research suggests that
a period of fasting followed by eating on
the new time schedule should help
entrain biological rhythms (Fuller et al
2008), possibly because some of our
body clocks are reset by food intake.
Real world application
The importance of research on shift
work and jet lag lies in the
applications it has to our everyday
lives, for example the use of artificial
lighting to entrain and reset circadian
rhythms. Being able to do this may
help avoid disasters such as the
Exxon Valdez.
The Exxon Valdez oil tanker ran aground at 12.04am in
1989 dumping more than 10 million gallons of oil into
Alaska, and killing thousands of marine animals and sea
birds. The Chernobyl nuclear power disaster began at
1.23am. Most lorry accidents occur between 4am and 7am.
Moore-Ede 1993 estimated the cost of shift worker fatigue
to be $77 billion annually as a result of both major accidents
and ongoing medical expenses due to shift work-related
illnesses.