After arriving home from an overseas trip recently and suffering greatly from the effects of jetlag I set about investigating this debilitating condition that makes the post-holiday days so miserable! Is there any science behind jetlag, and most importantly: is there any way we can reduce our risk of suffering post flight jetlag?

Jet lag & Circadian Rhythms

Well, the literature is very conclusive that jetlag is a genuine physiological phenomenon that can be explained by changes within the hypothalamus (which sits deep within our brain), a structure that helps us regulate our circadian rhythms which in turn help control temperature, sleep, appetite and hunger. The hypothalamus is like the master control clock of our body, the key to controlling all our cells and organs. The hypothalamus responds slowly to changes in time and light levels, which explains why we have no problems in our daily life as time ticks slowly along and light slowly fades to dark – the hypothalamus has time to adjust and continue our regular sleep/wake cycle. Each cycle of the circadian clock runs a fraction over 24 hours and is reset each day by a series of environmental cues such as light, temperature cycles, and food.

Put simply, jetlag is a disruption to our master body clock, or internal circadian rhythms – a discrepancy between this “inner time” (the normal sequence expected by our hypothalamus) and the “outer time” (a sudden change in time zone): our internal rhythm is out of sync with the environment! When you travel across multiple time zones, you are making changes that are faster than the master body clock can adapt to – as a result, your circadian rhythms, sleep patterns, cognitive ability, and metabolism are all thrown out of whack. It seems that the hypothalamus can adjust to up to 90 minutes of time zone difference, but not a lot more. This also helps explain why even seasoned travellers don’t “get used to” jetlag, as you can’t condition yourself to lessen the effect – it’s all to do with your sleep/wake cycle and exposure to light.

Some of the jetlag experts say that for every hour of time zone difference, you will need one full day to recover. So if you travel from Barcelona to Melbourne – a time difference of 8 hours – then under this theory it would take 8 days to recover.

Another theory I had previously thought strange is also supported by the science – direction of travel does make a difference! In a nutshell, “west is the best and east is a beast”! Why does direction make a difference? Because it appears that delaying our internal body clock is a lot easier than advancing it. Bright light exposure is the most powerful way to cause a phase shift – an advance or delay in circadian rhythms. Light in the early morning makes you wake up earlier (“phase advance”); light around bed time makes you wake up later (“phase delay”).

For example, if we fly across 8 time zones from Melbourne to Rome, your usual Melbourne bed time of (let’s say) 11pm will equate to 3pm in Rome. As we roam around Rome (and I’m sure the holiday excitement helps) the daylight makes it easy to remain awake for longer (remember that light in the evening is delaying our internal body clock from resetting). However flying from Rome to Melbourne, your newly adjusted bedtime of 11pm in Rome equates to a time of 7am in Melbourne. So at your peak of tiredness this strong exposure to light is causing you to wake up, advancing your body clock and leaving you…jetlagged! And whilst getting a quick nap in during the day of your arrival might seem like a good idea, the suggestions are to keep the nap very short, or you will be confusing the already confused internal body clock even more!

There are a multitude of websites promoting various jetlag remedies and strategies, but preparing your body for a time zone change appears to make the most sense (rather than just coping with it once it happens). Particularly when travelling east there’s some evidence behind waking an hour earlier each day for three days before you travel, and if travelling west it’s the opposite.

You can actually calculate what you need to do with your sleep patterns (adjusting your circadian rhythms pre-flight) to minimise the effects of jetlag. Think of it like this – we advise people to do a “prehab” strength/exercise program to prepare for upcoming surgery, this is like doing a pre-flight sleep program to prepare for a time zone change. Take a look at this link (but there are many others around) for an example of jetlag calculations: ; is another interesting site.

Exercise and nutrition have also been suggested as factors worth considering in your jetlag fight plan. For those that exercise during early mornings, particularly outside in the light, you will know that these sessions can dramatically and positively affect mood and energy levels. Along with carefully planned food intake, exercise is thought to have an impact on jetlag. Tied in with nutrition, it is fairly well accepted that alcohol and caffeine during flights probably aren’t great for your potential jetlag experience, but staying well hydrated with water is good.

Melatonin is often talked about as a wonder supplement for sleep and jetlag. Melatonin is released within the brain and its release is closely correlated with the amount of light you are experiencing. Light suppresses the production of melatonin, whilst darkness stimulates its release which assists our sleep phase. So when arriving home in Melbourne at 7am dead tired, to an abundance of light, melatonin release would be suppressed making sleep more difficult and disrupting the natural circadian rhythm. That’s why many people can find melatonin an effective supplement to aid sleep, but it certainly beyond the scope of this article or my expertise, to recommend taking melatonin!

Jet lag’s no fun, however it seems taking a few simple precautions before, during and after you travel can make an enormous difference, helping you recover much more quickly. It seems that seeking or avoiding light at the right time is critical, and a “pre-flight sleep program” can make a huge difference.

Happy and safe travelling!


Anthony Lance

SSPC Physiotherapist


References available on request.