Our body clock
Every cell in our body has a natural circadian (24-hour) rhythm, which is controlled by our body clock, located in the brain. For example, the circadian rhythm in alertness ensures that we are awake and active during the day, and asleep at night. This 24-hour cycle is maintained by a balance between internal (e.g. the rhythm of melatonin production – the sleep hormone) and external stimuli, mainly light, but also activity, meal and sleep times, and has to adjust when we travel across time zones. However, the body clock is unable to adjust quickly to a new time zone. This means our body clock becomes out-of-sync with the environment at the new location, and will only gradually synchronise to the local time, adjusting by approximately 1h per day following travel to the east and 1.5h per day following travel to the west. During this period, individuals may suffer a condition known as jet lag.
What is jetlag?
Jetlag is the unpleasant experience we feel when the circadian rhythms are out of alignment – both with the local pattern of day and night and with each other, as different body rhythms adjust at different rates. We know from research that the ‘master’ body clock, located in the brain, responds most to light, while other parts of our body (e.g. the stomach) also have clocks that are more influenced by meal times. Jet lag might be made worse if the clocks in different parts of our body are out-of-synch with each other and with the local time.
Subjective symptoms of jetlag may include sleep loss, fatigue, loss of mental efficiency, increased irritability, elevated daytime sleepiness and gastrointestinal disturbance. The duration and severity of jetlag, and the recovery time required, depends mainly on how many time zones have been crossed. Recovery is easier when travelling westwards (it is easier to delay sleep and wake up later) than travelling eastwards (when we have to fall asleep earlier and wake up earlier), but always more difficult when more time zones are crossed. Evidence also suggests that individuals who prefer later sleep times (evening types, or ‘owls’) cope better with jet lag compared to morning types (or ‘larks’). This is because evening types have been shown to adapt more easily to new schedules. For example, evening types can delay and extend their sleep whereas morning types are less flexible, particularly in relation to waking times.
Jetlag vs ‘travel fatigue’
Jetlag differs from simple ‘travel fatigue’. When we are jetlagged, our body clocks are out-of-sync, while ‘travel fatigue’ is purely linked to the journey, and usually resolves after a good night’s sleep.
Long flights, or long road journeys, can leave us feeling very tired – usually due to time spent in a cramped environment, with limited movement and poor sleep. In addition, when flying, we often don’t drink enough water which can make things feel worse. This ‘travel fatigue’ will usually resolve once you have settled into your destination and had a good night’s sleep, but it can leave you at risk straight after the journey. For example, sleep deprivation can lead us to make poor decisions, and leave us more at risk of road accidents when driving. If you have less than 5 hours of sleep, the data shows that the risk of being involved in a sleep-related vehicle accident is 3 times higher. After a long travel, exercise caution when deciding if you are able to go straight to work or drive – in many cases, it is likely to be safer to check in to a hotel and start work or drive after a night of sleep.
Elevated levels of sleepiness, are more likely after a long-haul flight. This can affect our driving performance. The exact impact may be different for each of us, depending on our individual circumstances, for example, how much ‘sleep debt’ has been accumulated in the prior few days. Research shows we are good at assessing our levels of sleepiness in the short term, but employees need to be aware of the early signs that their performance might be degraded and that they maybe should not drive.
If you are experiencing early signs of sleepiness (yawning, postural changes/fidgeting, and frequent eye blinks), setting off for a long drive is not recommended.
How do I best adapt to a new time zone?
If you are crossing multiple time zones and you will be in your new location for more than a few days, adapting to local time is the best policy. Everyone varies, but you may find it easier to adapt if you use one or more of the following strategies:
- Select your flight timing carefully – flights associated with the least amount of time between sleep opportunities seem to help with quicker adaptation
- If possible, try to begin sleep adjusting a couple of days before departure
- When crossing up to 5 time zones, matching your behaviour to the new time zone may help speed up adaptation
- Bright light is very powerful in helping our body clock adjust. See below section on light exposure for potential strategies
- Power naps (up to 20 minutes) can help if you are experiencing sleep disruption as a result of jet lag. However, avoid longer naps during the daytime at the new location as much as possible.
Light can help you adapt – but you have to time it right. This timing depends on the number of time zones you have crossed and the direction of travel:
Eastbound travel: Aim to get light exposure (either outside or bright inside light) between mid-morning and mid-afternoon in the new time zone. (For every extra time zone that you cross, move the start and end times of this window later by 1h). You should also avoid light at specific times of day, to help adjust. Avoid light in a ‘band’ 6h wide that ends 2h before the ‘light seeking’ window.
Westbound travel: The same principles apply – but the local timing of the light exposure is different. For every extra time zone that you cross, move the start and end times of this window earlier by 1h. When travelling west, avoid light in a ‘band’ too – also 6h wide – although this window begins 2h after the ‘light seeking’ window ends.
Electronic devices: Phones, tablets and computers also emit the same blue light that we find in daylight, and so disrupt your adaptation – avoid looking at them close to bedtime, or if you wake up in the night. You can further reduce the impact of these digital devices by installing blue-light reduction apps or using night mode.
What about melatonin?
Melatonin is the hormone released by the body in the darkness that prepares our body for sleep and is one of the two main ‘time-givers’ for our body clock (the other being the light-dark cycle). It is also possible to buy artificial melatonin in tablet form, which some people use to speed up the adaption of the body clock to a new time zone. Melatonin can make you fall asleep (like hypnotics such as benzodiazepines), taking it before work may be banned under your Company’s Drug and Alcohol policy. Buying melatonin is also illegal in some countries. Because of this, it is really important that you consult a doctor if you are considering taking melatonin.
I am an employer, what can I do?
Manage sleep loss and jetlag associated with company travel
- Consider the impact of travelling on jetlag, fatigue and alertness as part of your company risk identification protocols
- Provide employees with the information to allow them to make an informed decision about whether or not they are safe to undertake a long drive on company business or drive home following a long flight.
- Information should also be provided on what to do if the employee identifies that they are too tired to drive safely to help the employees to manage this decision.
- In the post-pandemic world, we are still seeking the balance between in-person and online meetings and events. When work needs to be carried out face-to-face, rather than going straight on-site, fly people in the day before, to allow for a night of sleep before work/meetings the next day. This will help reduce the effect of ‘travel fatigue’.
- Keep in mind that jet lag can affect performance for a few days in the new destination, so supervisors should be aware of potentially increased sleepiness levels among team members who have recently travelled, especially in high-risk conditions
- Where a trip must involve stopping in multiple different destinations – particularly if they are in different time zones – try and schedule the trip to aid adaptation. Ensure that adequate rest is planned for the trip, as stopping in multiple destinations may exacerbate jet lag symptoms.
- Develop a ‘Recovery’ policy for individuals returning home after long-haul business travel – jetlag and sleep loss will impact people after trips too; recovery time before returning to work will reduce the chances of performance decrements and errors – this may be allowing workers an additional rest day after returning home, or by providing an option of an additional rest day for those who do not feel well-rested enough to come into Where additional time to rest cannot be accommodated, try and schedule relatively low-risk and forgiving tasks on the first day back.
In order for the company to collect information on elevated fatigue, and know where mitigations could be applied, the company should have a policy that encourages self-reporting of all fatigue issues. Issues may be related to shift work, jetlag, or could be due to personal reasons. An ‘incident’ does not Our body clockEvery cell in our body has a natural circadian (24 hour) rhythm, which is controlled by our body clock, located in the brain. For example, the circadian rhythm in alertness ensures that we are awake and active during the day, and asleep at night. This 24 hour cycle is maintained by a balance between internal (e.g. the rhythm of melatonin production – the sleep hormone) and external stimuli, mainly light, but also activity, meal and sleep times, and has to adjust when we travel across time zones. However, the body clock is unable to adjust quickly to a new time zone. This means our body clock becomes out-of-sync with the environment at the new location, and will only gradually synchronise to the local time, adjusting by approximately 1h per day following travel to the east and 1.5h per day following travel to west. During this period, individuals may suffer a condition known as jet lag.
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Jospehine Arendt (2008) Managing jet lag: Some of the problems and possible new solutions, Sleep Medicine Reviews, 13:4, 249-256
Jim Waterhouse, Thomas Reilly, Greg Atkinson, Ben Edward (2007) Jetlag: trends and coping strategies, Lancet, 369, 1117-29
Charles H. Samuels (2012) Jetlag and travel fatigue: A comprehensive management plan for sport medicine physicians and high-performance support teams, Clin J Sport Med, 22, 216-273
Watling, C. N., Armstrong, K. A., & Radun, I. (2015). Examining signs of driver sleepiness, usage of sleepiness countermeasures and the associations with sleepy driving behaviours and individual factors. Accident Analysis & Prevention, 85, 22-29.