Jet Lag: Minimizing It’s Effects with Critically Timed
Bright Light and Melatonin Administration
Barbara L. Parry, M.D.*
Professor of Psychiatry, University of California,
San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0804,
USA
‘‘Truly the light is good and it is beneficial
for the eyes to behold the sun.’’
— Ecclesiastes 11:7
Abstract
The symptoms of jet lag cause distress to an
increasing number of travelers. Potentially they
may impair sleep, mood and cognitive performance.
Critically timed exposure to bright light and
melatonin administration can help to reduce symp-
toms. Bright light is one of the most powerful
synchronizers of human rhythms and melatonin
serves as a ‘‘dark pulse’’ helping to induce night-
time behaviors. Thus, enhancing day and night
signals to the brain, appropriate to the environ-
mental light/dark cycle of the new time zone, can
serve to reestablish adaptive timing relationships
between the body’s internal biological rhythms and
the external environment, and thereby reduce the
symptoms of jet lag. Specific recommendations
using bright light and melatonin for eastward and
westward travel before and after departure are
provided for time zone changes of up to 6, 7–9 and
10 or more hours.
Introduction
An increasing segment of the population experiences
the symptoms of jet lag. These groups include not only
tourists, but also transmeridian business travelers,
military personnel, politicians, diplomats, athletes and
night shift workers, whose functioning and performance
can be impaired by the attendant sleep deprivation that
may occur. Leger et al. (1993) reported that among 507
business travelers, nearly half suffered from fatigue
during international business trips, approximately 78%
reported disturbed sleep and approximately 27%
complained of intellectual disability. It is interesting to
speculate that the Yalta conference may have had a
different outcome if its major participants had not been
suffering from symptoms of jet lag.
Jet lag is characterized by symptoms of fatigue,
lethargy, mood changes, cognitive impairment,
gastrointestinal disturbances and sleep disturbances.
It results from a desynchrony between the endogenous
circadian clock that regulates important biological
rhythms such as melatonin, cortisol and the core body
temperature rhythm and the sleep-wake cycle regu-
lated largely by the environmental light/dark cycle.
Normally the body’s internal biological rhythms are
synchronized with an individual’s approximately 24-h
sleep/wake cycle and the environmental light/dark
cycle. With travel to a different time zone, in which
the environmental light/dark cycle no longer coincides
with the same time intervals as those of the body’s
underlying biological rhythms, the traveler, for exam-
ple, often must try to sleep at times of the day conducive
to waking, not sleeping.
Light is one of the most powerful synchronizers
of human circadian rhythms. Light in the morning
advances circadian rhythms; light in the evening delays
them. Perhaps because the human species has ad-
apted over the years to fire and indoor lighting, however,
it generally requires light in the range of 2,500 lux (five
times the intensity of normal room light of about 500 lux)
to significantly shift human rhythms. Wavelengths in the
blue-green spectrum (400–500 nanometers) appear to
be the most effective in shifting human rhythms. Based
on these principles, bright light then can be used to help
advance underlying biological rhythms when under-
going a phase-advance (in which rhythms shift earlier)
associated with eastward travel, and to delay rhythms
when undergoing a phase-delay (in which rhythms shift
later) associated with westward travel. Alternatively, by
wearing dark sunglasses or goggles or avoiding light
exposure at critical times during evening hours (based
on the body’s internal clock time, which may be different
from the local time) after eastward flight can help
prevent the delay of rhythms antagonistic to the
phase-advance needed to adjust to the earlier time
zone. Likewise, avoiding morning light on westward
travel helps to prevent a phase-advance antagonistic to
the phase-delay needed to adjust to the later time zone.
Advancing or delaying underlying biological rhythms
with light serves to shift these rhythms more rapidly than
would normally occur and allow them to be more in
accordance with the environmental light/dark cycle of
the destination zone. With his/her own biological rhy-
thms readjusted to the new time zone, the traveler then
can sleep at a circadian phase more congruous with the
environmental light/dark cycle. Without specific inter-
ventions, an individual’s biological rhythms generally
shift 1–2 h/day with changing time zones (although this
change generally occurs more slowly for older indivi-
duals). For destinations with time zone differences of
less than 3 h, jet lag symptoms are minimal. For time
zone changes for 3 h, however, interventions can
*For correspondence. Email bparry@ucsd.edu; Tel. (619) 543-5592;
Fax. (619) 543-7519.
J. Mol. Microbiol. Biotechnol. (2002) 4(5): 463–466.
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help speed the process of adaptation. The primary
mode of action of light in shifting rhythms is thought to
be mediated by stimulation of impulses originating in
the retina and propagated via the retinohypo-
thalamic tract to the suprachiasmatic nucleus of the
anterior ventral hypothalamus, the anatomic location of
the biological clock. Via a multisynaptic pathway, fibers
subsequently impinge on primarily B-adrenergic recep-
tors in the pineal gland where serotonin is converted to
melatonin by a process of acetylation and methylation.
From the majority of evidence available to date, the
eyes then need to be open to receive the light impulses
in order to shift human rhythms, although a recent
report by Campbell and Murphy (1998) suggest that
light exposure to vascular areas such as the popliteal
region (behind the knee) also may shift these rhythms.
The hormone, melatonin, synthesized from seroto-
nin in the pineal gland, also can serve to shift human
circadian rhythms. It serves as a chemical ‘‘dark pulse’’
indicating to the body that physiological responses and
behaviors appropriate to night are to be instituted. Thus,
it serves as a chemical transducer which sends a signal
to the brain opposite to that of light: Melatonin admin-
istration in the morning delays circadian rhythms;
melatonin in the evening advances them. Since mela-
tonin is regarded as a food supplement, it is not
approved by the Food and Drug Administration. At
present, therefore, it generally must be obtained from
health food stores, where dosages may not be regulated
accurately. Studies to date indicate that <1 mg is suf-
ficient to shift human rhythms. Slightly larger dosages
(5 mg) may have soporific side effects and may be used
to help induce sleep, although the use of melatonin as a
hypnotic for insomnia has not been established in
persons sleeping at normal circadian phases. It seems
to be most useful as a chronobiotic, to induce shifts in
circadian phase for short term usage. The safety and
efficacy of long term use has not been established.
Bright light has its maximum phase-shifting effects
when administered in the middle of the night; alterna-
tively, melatonin has its most potent phase-shifting
effects during the middle of the day. It is not practical to
administer light in the middle of the night, and admin-
istration of melatonin in the middle of the day at higher
dosages may induce sleepiness. Thus to mitigate jet lag
symptoms, often combining (not simultaneously) light
and melatonin administration, each approximately at
their critical time points, can be beneficial. The timing of
the light or melatonin administration should be based
on internal body clock time at the point of departure,
not the local time of the destination zone, as the inter-
nal clock time must gradually shift to that of the new
local time zone. Critically timed light administration of
sufficient intensity then can be used, in conjunction
with melatonin in appropriate dosages, to shift human
circadian rhythms so that they are more in phase with
the environmental light/dark cycle of the destination
time zone. By realigning these rhythms, the traveler
can adjust to the new time zone more rapidly and
thereby minimize the symptoms of jet lag. Such inter-
ventions may reduce symptoms by up to 50%, but they
may not be beneficial in all individuals. More specific
recommendations for light and melatonin administra-
tion for eastward and westward change in time zones
of 3–6, 7–9 or 10 h, before and after the day of
departure are described below. (The effects of 1–2 h
time zone changes generally are minimal, but the same
recommendations for 3–6 h. time zone changes also
would apply in these cases).
Travel from West to East
In going from west to east, the traveler is shifting to an
earlier time zone and thereby undergoing a phase-
advance. In order to adjust to the new time zone, he/she
must shift their internal biological rhythms earlier. Since
the sleep/wake cycle can be more readily shifted than
other biological rhythms, treatment is aimed at shifting
the timing or phase of melatonin, cortisol, core body
temperature and other internal rhythms, that once re-
aligned, allows sleep to occur more readily at app-
ropriate circadian phases. Ideally, interventions should
be instituted prior to departure, and depending on the
time zones crossed, maintained for 3–4 days following
departure.
For a 3–6 h (h) eastward time zone change (for
example, 3 h. from Los Angeles, California to New York
City or 6 h. from New York City to Paris, France):
The day before and the day of departure: Light: Get
bright light (outdoor if possible, or from commercially
available light sources-see references, Rosenthal,
1998) in the morning shortly after awakening (before
9:00 a.m.) to advance rhythms. For light intensity in the
range of 2,500 lux, 2 h. of exposure is required; for
10,000 lux, 30 minutes. Avoid evening light exposure
that would delay circadian rhythms. Melatonin: Before
departure, take melatonin in the afternoon (about
3:00 p.m.) in small dosages (< 1 mg to avoid sleepi-
ness) to help advance circadian rhythms. For eastward
travel of 6 time zones (e.g. New York City to Paris,
France at specific times of the year), taking melatonin at
3:00 p.m. in the departure time zone (in New York City)
would be 9:00 p.m. in the destination time zone (in
Paris). Allowing 1–2 h. for absorption of the drug, taking
melatonin in New York City in the mid-afternoon would
be prior to bedtime in Paris. By using this intervention at
this time, the brain would receive the chemical message
that it was ‘‘dark’’ and begin to respond by inducing
nighttime behavior, including sleep, in preparation for
the new time zone change. For eastward travel of 3 h.
(e.g., from Los Angeles, California to New York City), it
would not be necessary to take the melatonin until 6:00
p.m. (Los Angeles time), as bedtime in the destination
zone (New York City) at that time would be 9:00 p.m.,
although melatonin in the midafternoon (at 3:00 p.m.
Los Angeles time) is likely to induce maximum phase-
shifting effects (Lewy et al., 1998).
Upon arrival: Light: Get morning light to advance
circadian rhythms and avoid evening light that would
delay them. Melatonin: On day 1, take the medication
when it is the same time at your destination point that
you took it the previous day at your departure point. For
example, if you took the melatonin at 3:00 p.m. in New
464 Parry
York City prior to departure, take melatonin at 9:00 p.m.
upon arrival in Paris. As circadian rhythms advance
1–2 h. each day with time zone changes, on day 2 and 3
after arrival in the destination zone, take melatonin
1–2 h. earlier each day. For example, upon arrival in
Paris from New York City as described above, if you
took melatonin at 9:00 p.m. on day 1, take it at 7:00 or
8:00 p.m. on day 2, and 6:00 or 7:00 p.m. on day 3.
For a 7–9 h. eastward time zone change (for exam-
ple, from Los Angeles, California, to London, England):
The day before and the day of departure: Light:
Get morning light to advance circadian rhythms, and
avoid evening light that would delay them. Melatonin:
Take a small dose (< 1 mg) of melatonin about
2:00 p.m. (about 10:00 p.m. destination time).
Upon arrival: Light: Avoid morning light (as it would
be evening time at your departure point, reflective of the
timing of your own internal rhythms), which would delay
circadian rhythms, antagonistic to the desired phase-
advance. Get afternoon light (as this time would be
morning in your departure zone), to advance circadian
rhythms. Melatonin: Take melatonin (a larger dose of
5 mg is appropriate to induce sleepiness, a side-effect
of higher dosages) prior to bedtime when it is the same
time at your departure point that you took it the previous
day. For example, if you took melatonin at 2:00 p.m. Los
Angeles time prior to departure (10:00 p.m. London
time), upon arrival, take melatonin at 10:00 p.m. London
time on day 1 of arrival. On day 2 and 3 after arrival,
take melatonin 1–2 h. earlier each day (for example at
9:00 p.m. on day 2 and 8:00 p.m. on day 3).
For 10 or more eastward time zone changes (for
example, from Los Angeles to Jerusalem): Note that for
a time zone change near 12 h., it is easier to delay rather
than advance rhythms, as the human free-running pe-
riod (the duration of a rhythm without external influences
such as the light/dark cycle) is slightly greater than 24 h.
Therefore, given the human tendency to delay rhythms
on a daily basis when there are not external constraints,
jet lag symptoms generally are shorter and less severe
for westward travel (when undergoing a phase-delay)
than for eastward travel (when undergoing a phase-
advance).
The day before and the day of departure: Light:
Get light in the evening and avoid light in the morning
to delay circadian rhythms. Melatonin: Take melatonin
(< 1 mg) on awakening.
Upon arrival: Light: Get morning bright light, and
avoid light the rest of the day. Melatonin: On day 1, take
melatonin when it is the same time at your departure
point that you took it the previous day. For example, if
you took melatonin at 7:00 a.m. Los Angeles time before
departure, take melatonin at 5:00 p.m. Jerusalem time
upon arrival. On day 2 and 3, take melatonin 1–2 h.
earlier each day, for example at 4:00 p.m. on day 2 and
3:00 p.m. on day 3.
Travel from East to West
For 3–6 h. westward time zone change (for example,
3 h. from New York City to Los Angeles, California and
6 h. from Paris, France to New York City):
The day before and the day of departure: Light:
Get light late in the day to help delay circadian rhythms
and avoid light early in the day that would advance
circadian rhythms. Melatonin: Take melatonin (< 1 mg
to avoid sleepiness) on awakening.
Upon arrival: Light: Get light late in the day to help
delay circadian rhythms and avoid light early in the day
that would advance them. Melatonin: Take a small dose
(< 1 mg) of melatonin on awakening. On days 2 and 3,
take melatonin 1–2 h. later than on the previous day.
For 7–9 h. westward time zone change (for exam-
ple, from London, England to Los Angeles, California):
The day before and the day of departure: Light:
Get light in the evening to delay circadian rhythms and
avoid light in the morning that would advance them.
Melatonin: Take a small dose (< 1 mg) of melatonin on
awakening.
Upon arrival: Light: Get midday light (that repre-
sents evening light body clock time at your point of
departure in London) to delay circadian rhythms and
avoid late-day light (that represents morning light body
clock time in London) which would advance circadian
rhythms. Melatonin: Take melatonin on awakening
(< 1 mg) to delay circadian rhythms. On days 2 to 4
after arrival, take a small dose of melatonin (< 1 mg)
1–2 h. later each day than on the previous day (e.g., at
8:00 and 9:00 a.m. on subsequent days Los Angeles
time).
For 10 or more westward time zone changes (for
example, from Jerusalem to Los Angeles):
The day before and the day of departure: Light: Get
bright light in the evening to delay circadian rhythms
and avoid light in the morning that would advance them.
Melatonin: Take a small dose (< 1 mg) of melatonin on
awakening.
Upon arrival: Light: Get morning light (which would
be evening light Jerusalem time) to help delay circadian
rhythms; avoid evening light (which would be morning
light in Jerusalem) that would advance circadian
rhythms. Melatonin: Take melatonin (5 mg to induce
sleepiness if needed) when it is the same time at the
point of departure that you took it yesterday. For
example, if traveling from Jerusalem to Los Angeles,
if you took melatonin at 7:00 a.m. Jerusalem time
before departure (9:00 p.m. Los Angeles time), take
melatonin at 9:00 p.m. Los Angeles time on day 1 of
arrival and take it 1–2 h. later than on the previous day
for days 2–4 after arrival (for example, at 10:00 p.m.
and 11 p.m. on subsequent days).
Summary
Appropriately timed bright light and melatonin admin-
istration, by helping to adjust underlying circadian rhy-
thms to the new time zone, can serve to mitigate the
symptoms of jet lag. Bright morning light advances
circadian rhythms; bright evening light delays them.
Melatonin in the evening advances circadian rhythms;
melatonin in the morning delays them. These princi-
ples, applied to the timing of the body’s internal
biological rhythms, can advance rhythms for eastward
travel and delay them for westward travel. Reducing
Jet Lag: Minimizing It’s Effects 465
the symptoms of jet lag by these methods can lessen
the mood, cognitive and behavioral symptoms resulting
from these desynchronized rhythms.
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