shows internal body clocks become desynchronized under jet-lag
new study demonstrates that internal time clocks in mammals, involving
multiple organs, reset at different rates following changes in
light cycles. This disruption of the normal relationships among
circadian rhythms throughout the body may explain why air travelers
experience malaise after crossing several time zones and may point
to more serious health issues for shift workers.
at U.Va.'s Center for Biological
Timing, whose findings were reported in the April 28 issue
of the journal Science, studied the physiology of the body's reaction
to abrupt shifts in cycles of light.
nature, light shifts occur slowly as the seasons change,"
said Michael Menaker, Commonwealth Professor of Biology. "Organisms,
therefore, have several months to adjust to the changes. But transmeridian
flight is an unnatural event for the body. It causes very abrupt
light cycle shifts. The body is not naturally prepared for this
sudden change. Once the relationships between the various oscillators
are disrupted, the normal function of the organs may be compromised."
used brain, skeletal muscle, liver and lung tissue from transgenic
rats to collect their data.
rat tissue included a known clock gene indicator from a mouse
that is spliced with a glowing "tag" (a firefly enzyme).
The tag is activated when the clock gene responds, or is transcribed,
during changing light cycles. Menaker and his team were able to
"reset" the brain and organ clocks -- the circadian
rhythms -- forward by six hours or back by six hours, mimicking
the effects of trans-Atlantic travel.
demonstrated clearly that both brain and peripheral tissues are
rhythmic when they are removed from the animal and held in culture
conditions. This is new information, but was suspected. What is
surprising is that while the central oscillator in the brain keeps
cycling for up to one month, the peripheral tissues rapidly lose
their rhythmicity in culture. We now believe the central oscillator
in the brain is the key timer that synchronizes the peripheral
clock cycles. This helps us understand biologically what happens
in an organism when its light cycle is suddenly shifted."
the symptoms of occasional jet lag may be annoying, the new findings
may imply that the physiological effects of rotating shift work
could be more serious, he warned.
percent of the U.S. workforce are shift workers," he said.
"Our findings suggest that frequent irregular light cycle
shifts may have biological repercussions. Shift workers, for example,
often experience reduced alertness, fatigue, ulcers and poor digestion.
We do not know yet the full extent of the health issues that may
result from regular disruption of circadian rhythm synchrony.'
to Menaker, most catastrophic accidents -- such as the Exxon Valdez
grounding, and the Three Mile Island and Chernobyl nuclear power
plant incidents -- are the result of human error, commonly occurring
among shift workers late at night.
people are trying to adjust to abnormal sleep and wake cycles,
they tend to lose focus, become fatigued more easily and generally
don't feel as healthy as they normally would," he noted.
"We are showing that a physiological change is occurring.
The ramifications for health and performance are real and potentially
researchers who conducted the study include Shin Yamazaki, the
principal investigator, Michikazu Abe, Gene Block and Menaker.
Six researchers from the University of Tokyo and the New Technology
Institute in Japan also participated.