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The University of Sydney Page 2
OLET1510 Health
Challenges: Sleep
Jetlag: just a transient inconvenience?
Dr Yu Sun Bin
The University of Sydney Page 3
Jetlag: What is it?
– Mismatch between internal circadian
rhythm and external light-dark cycle
– Caused by travel over multiple time
zones
– More time zones = more severe
– Travel east = more severe
– Wide range of symptoms
– Rule of thumb: 1 day to adapt per
time zone crossed
The University of Sydney Page 4
Human circadian rhythm
Image source: Daniel Gallan
The University of Sydney Page 5
Jetlag: just a minor inconvenience?
Major issue for travellers, especially
where performance is critical
– Politicians and diplomats
– Business travellers
– Defence personnel
– Airline crew
– Athletes
–
The University of Sydney Page 6
Studies of athletes in countries spanning multiple time zones
Numbers indicate time zones (UTC± hours)
Image source: United States Central Intelligence Agency, Standard Time Zones of the World
– Disadvantage for the team who
crossed time zones to compete
– Size of disadvantage related to
number of time zones crossed
– Size of disadvantage larger for
eastward compared to westward
travel
The University of Sydney Page 7
Studies of athletes (1)
– Australian National Netball (Bishop
2004 J Sci Med Sport)
– Australian A-League Soccer (Goumas
2014 J Sci Med Sport)
– Home advantage 58%, increased
when visitors crossed more time zones
Image credit: https://vic.netball.com.au/news/media-release-netball-most-popular-
team-sport-for-girls/
The University of Sydney Page 8
Studies of athletes (2)
– US Major League Baseball (Song et al
2017 PNAS)
– Conceded more home runs
– US National Football (Jehue et al 1993
Med Sci Sports Exerc)
– US National Basketball Association
(Steenland & Deddins 1997 Sleep)
– Best performance after 3 days rest
– Difference between home/travel
declining over time (1980s to mid-
1990s)
– Becoming more aware of jetlag?
The University of Sydney Page 9
Jetlag: just a minor inconvenience?
Major issue for travellers, especially
where performance is critical
– Politicians and diplomats
– Business travellers
– Defence personnel
– Airline crew
– Athletes
Complex, cognitive performance
is most impaired by circadian disruption
and sleep deprivation
–
The University of Sydney Page 10
Jetlag: the size of the problem
– No formal estimates of cost to
travellers, businesses, or government
– Qantas Group carried 17.8 million
passengers on international flights in
2017
– If reduce jetlag by ½ day per
passenger per flight = 8.9 million
days time-saving
– Median income = $220 per day =
$1.958 billion saving in work hours
– This is a conservative estimate!
Image credit: Daniel R Strebe 2011 Gall-Peters projection
The University of Sydney Page 11
Jetlag: the size of the problem
– Globally: 2.4 billion passengers
on international flights per annum
– Unclear the number of time zones
crossed in each instance
– Excludes domestic flights which
can also include time zone
crossings
– Numbers expected to double by
2035: 4.8 billion passengers per
annum
The University of Sydney Page 12
OLET1510 Health
Challenges: Sleep
Jetlag solutions
Dr Yu Sun Bin
The University of Sydney Page 13
Revision: Circadian terminology
– Period: 1 cycle of the circadian
rhythm (~24 hours)
– Phase: a point in the rhythm
– Phase shift: change in the timing
of the rhythm
– Phase advance: shortening the
day, bring the cycle forward
– Phase delay: extending the day,
postponing the cycle
The University of Sydney Page 14
Severity of jetlag determined by:
– Direction of travel
– Eastward travel is associated with
worse jetlag than westward travel
– Travelling west, sunrise is later
– E.g. New Year’s Eve is celebrated first
in New Zealand
– Number of time zones crossed
– Destination time zone – origin
time zone (hours)
Image source: United States Central Intelligence Agency, Standard Time Zones of the World
The University of Sydney Page 15
Time zones
– Social convention defined
originally as local solar time
– Noon = time sun is directly
overhead and casts no shadow
– For every 15-degrees longitude, 1
hour time difference
– Not applied consistently e.g.
China, Adelaide
– Offset from Universal Coordinate
Time (UTC±)
– E.g. Sydney is UTC +10/+11,
Santiago is UTC -4/-3
– At International Date Line, solar
time is the same, but +1 day on
west of line (-1 day to the east)
Image source: United States Central Intelligence Agency, Standard Time Zones of the World
The University of Sydney Page 16
Why eastward travel is more difficult than westward travel
– Period of human circadian rhythm
needs to match 24-hour light-dark
cycle on Earth
– Majority of people (75%) have a
circadian rhythm longer than 24 hours
– Easier to delay circadian rhythm i.e.
extend the length of a day and live a
day longer than 24 hours
– More difficult to advance and shorten
the cycle
– Some people with circadian period
<24h period may find it easier to
advance than delay
Figure from Hasan (2012) FASEBJ: Participants aged 20-32 years
The University of Sydney Page 17
Example: Flying between Sydney and London
– Sydney to London: travel towards
the west requires phase delay
– London to Sydney: travel towards
the east requires phase advance
– It is possible to advance/delay for
west/east ward travel, but these
requires >12h shift in rhythm
The University of Sydney Page 18
Example: Flying between Sydney and London
– Flying to London from Sydney:
– destination – origin = (UTC 0) – (UTC +10) = -10 hours
– phase delay by 10 h (or advance by 14 hours)
– Flying to Sydney from London:
– destination – origin = (UTC +10) – (UTC 0) = +10 hours
– phase advance by 10 hours (or delay by 14 hours)
24h local time
The University of Sydney Page 19
Evidence-based jetlag solutions
– Recall: intrinsic circadian rhythm
shifts in response to external
zeitgebers
– Light
– Exogenous melatonin
– Response to zeitgebers
characterised by phase response
curves
The University of Sydney Page 20
Light (blue phase response curve)
– Greatest phase shift at night
– Biggest phase delay ~2-4am
– Biggest phase advance ~4-6am
– Around 4am = may cause shift in
wrong direction!
– But, depends on characteristics of
the light
– Light intensity (brightness)
– Light wavelength (colour)
The University of Sydney Page 21
Light intensity
– Intensity or “brightness” of light
– Bright light produces a stronger
phase shift
– Lux = standard unit of
measurement for light intensity (or
illuminance)
– Being outdoors is many times
brighter than indoor light
– Therefore, advice to spend time
outdoors after flight
The University of Sydney Page 22
Light wavelength
– “Colour” or
wavelength of the light
– Human circadian system
most sensitive to blue
light of wavelength
440–490nm
– Blue light is most
‘alerting’ during night-
time
The University of Sydney Page 23
Synthetic melatonin (red phase response curve)
– Effective for adults travelling over
5+ time zones (Herxheimer & Petrie 2002
Cochrane Review)
– Used as sleep aid; taken close to
bedtime at destination
– In Australia, prescription only
– Interaction with other medications?
– Unclear safety in children and
elderly
– Adverse effects in epilepsy and
pregnancy?
The University of Sydney Page 24
Evidence-based jetlag solutions: scheduling light and sleep
On arrival after flight:
– Spend time outdoors during the day,
even when cloudy/rainy
– Avoid light at night
– Use sleep as an opportunity to avoid
light (dark room, eyes closed)
– Jetlag apps or online calculators
may help you plan a schedule of
light and sleep
– But none of these have been
tested for effectiveness (Bin et al 2019
Sleep Med Rev)
The University of Sydney Page 25
Evidence-based jetlag solutions: before and during flight
Use time before and during flight to
get a head start on adaptation
– Days before flight, delay or
advance sleep/wake times by ½
to 1 hour each night (Eastman et al 2005
Sleep)
– Use light at night to help delay or
avoid light to advance
– Use the time during flight to start
living on destination time, including
meals https://www.jetlagrooster.com/
The University of Sydney Page 26
Circadian effects of jetlag well-recognised, but what about…
– But, jetlag = circadian disruption
+ travel fatigue
– Sources of travel fatigue:
– Sleep deprivation: difficult to
sleep on plane
– Studies show sitting upright
impairs sleep
– Sleep quality improves when
sleeping position is closer to the
horizontal
– Acceleration, vibration, noise,
reduced air pressure, varying
temperatures and humidity
levels during long flight
– Sudden changes in temperature,
humidity, pollution, altitude,
food quality on arrival at
destination
– These factors unexplored as ways to
ease fatigue linked to jetlag
The University of Sydney Page 27
Other jetlag advice
– Not flying (circadian disruption is
inevitable when crossing time zones)
– Fly westward
– Buy a seat that lets you lie down (no
sleep deprivation, less fatigue)
– May not be practical!
General health/wellbeing strategies:
– Hydration
– Healthy eating (meal timing,
macronutrient content)
– Movements and stretches
– Avoid stress and sleep deprivation
before flight
– Create comfortable physical
environment e.g. clothing, eye shades,
ear plugs
– Create comfortable psychological
environment e.g. personal space, quiet