Jet lag messes with your circadian clock, leaving you exhausted or wide awake at the wrong times. To combat it, control light exposure, adjust your sleep schedule, and use melatonin at the right moments. Apps like Timeshifter help you realign faster, and supplements like tart cherry juice may support your body’s rhythm.
How to shift your circadian clock to beat your jet lag
Author: Linda Rodriguez McRobbie
IN THE first flush of our relationship, my husband began taking a series of photos of me during our travels. In every one, I am asleep: sat on a chair at the Musée d’Orsay in Paris. Head on my chest in the back seat of a car in Kiev, Ukraine. On a train in France, mouth open, drooling. He is lucky I still married him.
Jet lag certainly isn’t pretty. Other than leaving you feeling exhausted – or wide awake – at the wrong time of day, a long flight across time zones can also cause gastrointestinal distress, off-kilter body temperature, headaches, irritability and cognitive impairment, all of which are much more serious for people who fly all the time, such as airline pilots. What can we do?
Many of us approach jet lag by prioritising sleep whenever we can, in order to counter the exhaustion. Even the National Health Service website for England recommends that you “change your sleep schedule to the new time zone as quickly as possible”, and many of us try to just knock ourselves out on overnight flights (often with the help of over-the-counter medicines or in-flight refreshments).
While this approach isn’t always wrong, it can sometimes do more harm than good. Instead, we need to think about jet lag in a more nuanced way, says Steven Lockley, a neuroscientist who was at Harvard University Medical School. “Jet lag really is about the body clock, it’s not about sleep,” he says.
Jet lag is the result of a sudden misalignment between the body’s established circadian rhythms and the environmental day-night cycle at a new destination. “These symptoms occur because our circadian clock, which drives our 24-hour rhythms in nearly all aspects of physiology and behaviour, cannot instantly reset to the new time zone,” says Victoria Revell at the University of Surrey, UK. This may seem obvious, but it points towards a different way of dealing with the problem: focus on resetting your body clock as efficiently as possible.
The most powerful way to do that is to strategically control exposure to light. Bright light tells the suprachiasmatic nucleus, a brain structure that sets the internal clock, to suppress the sleep-signalling hormone melatonin (see “What do hormones do to our sleep – and vice versa?”, page 37). But the blanket advice to get outside during the day in the new time zone isn’t always right. “Exposure to bright light at the wrong time of day can actually push your clock in the wrong direction and prolong jet lag,” says Revell.
Imagine you leave New York at 7 pm on a 7-hour flight to London. You land at 7 am local time, but your body thinks it is 2 in the morning. Exposure to bright light at that time would tell your body clock to stay up even later, explains Lockley. “So now, instead of having a 5-hour jet lag challenge, you might have a 6, 7, 8-hour jet lag challenge.” In this scenario, he suggests avoiding bright light by wearing sunglasses, even indoors, until around 10 am local time – or 5am in your body’s circadian time – to reduce that effect.
Light isn’t the only factor worth considering. Research by Revell and her colleagues has found that the best way to reduce circadian misalignment is a combination of strategic light exposure, gradually changing your sleep schedule before travel, and taking melatonin at the right time. Other cues can also help nudge your circadian clock in the right direction, including avoiding heavy meals late in the evening of your home time and taking caffeine early in the day, she says.
Even so, it can be hard to calculate and keep track of when to do all these things, especially when you are tired. There is, of course, an app for that, in fact several, with anecdotal evidence of efficacy, even if clinical trials are lacking. Lockley has developed one of these, called Timeshifter, that runs all the numbers for you, based on your flight plan and sleep patterns, and provides a bespoke timetable. All this starts a few days before your trip, to help minimise the cliff-edge transition from one time zone to another. The algorithms behind the app were partly developed to help astronauts regulate their circadian rhythms while in space.
Another is FlyKitt, which offers similar scheduling, but also recommends a regimen of supplements meant to be taken at specific times to alleviate symptoms of jet lag. These include vitamin C with tart cherry powder and melatonin with magnesium, and there is some evidence that they could help. For example, tart cherry juice – which went viral as the sleep-improving ingredient in TikTok’s “sleepy girl mocktail” – was found to increase overall sleep time and sleep efficacy, according to a 2023 analysis of several studies and a small, randomised controlled study. This might work by increasing the tryptophan available to be converted into melatonin (see “How does the microbiome influence our sleep?”, page 35). Melatonin can augment light exposure to shift circadian rhythm, but beware: the evidence for other supplements is less robust.
The next time I fly, I am going to focus on shifting my circadian clock – if only to lessen the chance of my husband catching me napping at yet another tourist spot.
Credits: TCA, LLC.