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Air travel, shift work and space
travel are modem activities that profoundly disturb the body's
inner biological or "circadian" clock, giving rise
to several minor (and in some cases serious) health problems.
Jet lag is a familiar disorder in which rapidly flying across
several time zones disrupts the body's circadian rhythm. Its
hallmarks are lightheadedness, difficulty concentrating, fatigue
and an inability to sleep well.
Crossing several time zones upsets
the biological clock
Although still a new scientific
field, "chronobiology" -- the study of innate biological
rhythms -- reveals some fascinating truths about the human body's
adaptation to air travel. The inner biological or circadian clock
produces rhythmic changes whereby our body is "primed"
for optimal activity and efficiency during the waking or daylight
hours and partially shut down" at night, with metabolic
changes that induce sleep -- a drop in body temperature, falling
levels of adrenaline (the stimulatory hormone from the adrenal
gland) and other subtle changes.
Experiments have shown that without
external time cues -- such as bedtime, mealtimes, work deadlines
-- the body clock runs slow, at cycles of about 25 hours, hence
its name, circadian clock (from the Latin circa for "about"
and diem for "day"). The natural rhythm of the circadian
clock was revealed by experiments on volunteers who stayed in
caves deep beneath the French Alps, free of all outside time
signals such as sunlight, watches, mealtimes, radio, and knowledge
of weather and temperature. Despite the total absence of environmental
cues, the isolated subjects retained rhythmic swings of body
temperature, hormone secretion, blood pressure, potassium levels
and sleep/wake cycles.
Zeitgeber ("time givers")
reset circadian cycles
Since humans have circadian cycles
naturally longer than 24 hours, our body clocks are constantly
reset to conform with mechanical clocks and adjust to the solar
swings of night and day, using environmental cues called "Zeitgeber"
(from the German Zeit for "time" and geber "to
give"). Environmental stimuli -- jobs, scheduled activities
and mealtimes -- act as Zeitgeber or "time givers"
that constantly force our circadian pacemakers to harmonize with
the world around us.
In addition, the changes of light
and dark affect melatonin (a hormone put out by the brain's pineal
gland, and parts of the eye). Melatonin secretion goes up in
the dark and is suppressed by light (either daylight or specially
bright artificial light). Melatonin can regulate reproductive
cycles in some animals, especially those that breed photoperiodically
(according to the length of daylight). Although not bright enough
to suppress human melatonin, ordinary electric light can alter
breeding patterns in hamsters and other animals. Studies are
underway to see if melatonin can combat jet lag.
Jet lag is due to circadian rhythm
upsets
Anyone who has flown across time
zones knows how disrupting it is to adjust to a destination that's
several zones east or west. Jet lag arises from a mismatch between
the circadian clock (which continues to run on the time of the
departure zone) and new time cues at the destination. For instance,
when a traveler arrives in Europe from Canada on an evening flight,
local European clocks point to early morning, while the traveler's
circadian clock still ticks on Canadian nighttime. Yet, on arrival
travelers are expected to operate efficiently just when their
inner rhythms are at their lowest ebb. Stomach upsets, loss of
appetite, an inability to fall asleep and poor concentration
are typical of jet lag or "travel dysrhythmia."
After a long flight eastwards that
crosses five or six time zones, we feel tired and our ability
to carry out mental tasks is diminished on the new time scale.
Our new bedtime is "all wrong" -- coming just when
alertness and mental processing are sharp, so it's hard to sleep.
The loss of sleep leads to a decreased ability to function well
and a pervasive sense of exhaustion.
The quality of sleep also changes.
Normally, we have "slow wave" sleep at the beginning
of a night's sleep, and rapid eye movement (REM) sleep towards
the end of the sleep period. After jet travel, sleep patterns
are out of kilter. REM sleep may be "squeezed out"
of its usual position and sleep seems to be of poor quality.
On subsequent nights the normal sleep pattern gradually reappears.
But while the sleep cycle generally adjusts within 2-4 days (a
few sleeping fitfully for 4-5 nights), body temperature can take
up to two weeks to adapt.
While a night or two of poor sleep
does not make much difference to performance, prolonged sleep
loss leads to declining ability for many tasks, particularly
those requiring vigilance. Declining mental acuity becomes more
pronounced as the total time without a "good sleep"
increases.
The symptoms of jet lag decline
after a few days as the body clock attunes to the new time zone,
with the help of new cues or Zeitgeber Attempts to lessen jet
lag have concentrated on minimizing the sleep loss and/or speeding
up the body clock's adjustment.
Worse going east than with westward
travel
Adjusting to eastwards time -- in
a phase-advance direction that shortens the day (as when crossing
the Atlantic to Europe), is tougher than adjusting to westward
travel -- in a "phase-delayed" manner that lengthens
the day (as when flying from Paris to Toronto). Researchers attribute
the discrepancy to the longer-than-24-hour natural circadian
period, which means that delaying sleep or bedtime is easier
than advancing it. One study found that body temperature took
two weeks to adjust for an eastward trans-Atlantic flight but
about 50 per cent less for the westward journey. Heart rate,
body temperature, adrenal hormone output and alertness readjust
about twice as fast going west as going east.
Overcoming jet lag means resetting
the body clock
Many remedies have been proposed
for combatting jet lag, including special diets, various drugs,
exposure to very bright light and, most recently, melatonin pills.
Exposure to daylight can help reset the biological clock particularly
right after arrival, but only if it coincides with schedules
in the new time zone. Adjustment of the body clock can be accelerated
by immediately falling in with activities in the arrival zone
("When in Rome, do as the Romans do"). Adopting local
hours for mealtimes, sleeping and daytime activities, at once
taking part in social functions are the best way to adapt quickly.
Travelers should rest in a quiet, darkened room when it is bedtime
even if not tired, and try to start the new day as others do,
even if they still feel sleepy. Naps are not recommended as they
tend to confuse the body about when it is day or night.
Prepare ahead to combat jet lag
One effective way to combat jet
lag is to prepare ahead by altering the circadian rhythms before
a trip. But the suggested preparation differs according to the
direction and length of the intended trip. For those planning
an extended stay abroad, experts suggest trying to shift the
rhythms a day or two before departure, and certainly during the
flight.
A successful anti-jet-lag strategy
is to do what locals at the arrival zone are already doing --
either eating, being alert or sleeping. If going from North America
to Europe and leaving in the evening, for example, minimize stimulation
on the plane and try to sleep or doze if possible, avoiding alcohol
and not chatting to fellow passengers. On arrival, maximal exposure
to local cues speeds adjustment. The best bet is to stay up,
be active, socialize and tune in to all the new local cues, allowing
the new Zeitgeber to retrain the circadian rhythms as quickly
as possible. After landing in daytime, resist the temptation
to snooze! Studies show that immediate exposure to local activities
and bright daylight can hasten circadian resynchronization better
than staying in a dimly lit room or "sleeping off"
the jet lag. However, for a mere two-day trip, with a speedy
return home, the wisest strategy may be not to shift one's circadian
clock at all, but, as far as possible, remain on Canadian time
while abroad and stay on home-base cues.
Melatonin pills may help
Melatonin, a methoxyindole compound,
is normally secreted into the bloodstream by the brain's pineal
gland during the evening and night, and suppressed by daylight
or exposure to very bright artificial light. In view of its resynchronizing
properties and ability to react to light and dark, melatonin
has been tried as a jet-lag remedy with considerable success.
In one study, 386 people who took melatonin (5 mg in a gelatin
capsule) either before the flight or on arrival had a self-rated
60 per cent reduction in jet lag symptoms on eastward flights
and 40 per cent less discomfort when flying west. Other studies
on flights between San Francisco and London (England) also found
that melatonin, given for 1-2 days before departure and on arrival
at the destination, improved adaptation. Subjects rated their
jet lag as far as "less than usual" when taking the
melatonin pills.
Melatonin reduces fatigue and improves
sleep in long distance travelers. The few side effects from melatonin
include slight nausea and "fuzziness" or lightheadedness.
So far, there are no reported contraindications. Controlled-release
forms seem even more effective. Details of how melatonin works
are beginning to emerge. However, it is not yet generally available
in all countries, and not in the U.S. or Canada, except on an
experimental basis.
Diets against jet lag?
Although controversial and of no
definitely proven benefit, a few authors promote anti-jet-lag
diets (one suggested diet was apparently tried by former U.S.
president Ronald Reagan). Most of these eating regimes rely on
the premise that protein stimulates release of brain transmitters
that promote alertness and waking activities, while carbohydrates
stimulate release of sleep-inducing neurotransmitters (such as
serotonin). Therefore, if flying East on an overnight flight,
try to sleep on the plane, eat only high-carbohydrate (starchy
or sugary) foods, and on arrival have a protein-rich breakfast
(such as bacon and eggs) to stimulate release of brain transmitters
that enhance alertness.
Caffeine (trimethylxanthine) in
coffee, tea or colas can advance or retard circadian clocks,
depending when it is ingested. Caffeine supposedly delays the
body clock in the morning, but advances it in the evening. So,
for an overnight eastward flight, caffeine might best be avoided
before and during the flight, but near arrival time, drinking
black coffee may advance the body clock. For westward travel,
some experts recommend refraining from caffeine altogether en
route.
COPYRIGHT 1995 Strategic Inc. Communications
Ltd.
COPYRIGHT 2004 Gale Group
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