Experiments
involving rats suggest that the body's liver, muscles and lungs each have
their own internal 'clocks'.
And
this could explain why jetlagged travellers, or workers changing shift
patterns, can feel genuine aches and illnesses because of the time
differences.
The
rat study, carried out by scientists in the US and Japan, and published in
Science magazine, found that the internal 'circadian' rhythms of muscle,
liver and lung can be thrown out of synchronisation with the main body
circadian cycle.
The
researchers linked a fluorescing firefly protein to a key circadian clock
gene in genetically modified rats, causing the rats' cells to emit light
when the clock gene was activated.
Jet
lag induced
The
researchers then induced jet lag in the rats by fast-forwarding or delaying
the light/dark cycles in the rats' environment and then studied the
circadian activity in different tissues trying adjust to the change.
The
clock in the brain re-set itself within just one revolution of the circadian
cycle, while the clocks in the muscle and lung took six cycles to re-set,
and the liver took more than 16.
It
can cope with the subtle seasonal changes which reduce or increase the
number of daylight hours - but cannot deal with sudden changes like those
caused by transatlantic travel.
So
even if the main cycle has been reset to a different time zone, the liver
may still be functioning out of step.
However,
it is not certain how accurately circadian rhythms in rats reflect those in
humans.
As
well as fatigue, jetlagged people can often have upset stomachs and aching
muscles.
The
researchers estimated that up to 20% of the US workforce is exposed to these
abrupt day to night or night to day shift changes.
Dr
Mary Morrell, a lecturer in sleep physiology at the National Heart and Lung
Institute in London, said that passengers flying long-haul across time zones
often complained of gastric symptoms.
"There
has been a lot of discussion about whether these separate parts of the body
have their own circadian cycles, and this is more evidence to support
it."
She
added that the trial would be extremely difficult to replicate in humans, as
it would involve keeping them in almost unethical conditions.