Heading to Europe

When preparing for a big trip, however, the rules around light don’t always apply. Travelling somewhere with a difference of several timezones or more requires a change in our light habits to help us adjust.

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If you were preparing to travel to Europe, which is behind Australian time, you might start to slow your body clock by using bright light in the evening for about three days before you fly. Any longer is unnecessary, says Cain.

“In this instance, turn the lights on, use your phone on max brightness: All the things you wouldn’t normally do,” says Cain. “It will gradually push your body with evening light, towards London time.”

This is because bright light in the morning pushes our body clock forward, while light in the evening pushes it back.

Before a recent trip to London, Cain stayed up slightly later each night with bright lights on. Then, on the flight, he used light therapy glasses to keep himself awake until about 5am Australian time.

“I was most of the way adjusted by the time I got there,” he says.

When to avoid light

Returning to Australia from Europe is trickier for our bodies.

The human clock tends to delay better than it advances, which is why people find it easier to travel west than east. This is compounded by the fact that we also often land in the morning when our bodies still think it is nighttime.

Typical online advice is to get lots of bright light in our destination, especially if it’s morning there. Following this advice can make the jet lag worse.

“In the middle of the night, there is a crossover point on the effect of light. You quickly go from maximum delaying effect of light (like a slowing of the clock) to maximum advancing (like a speeding up),” explains Cain.

If we are exposed to light during this time, it can slow our clocks even further, or it can send the whole system into a state where it doesn’t know what time it is, says Cain: “We refer to it as light hitting the singularity.”

The crossover point coincides with our core body temperature dropping to its lowest point, about 90 to 180 minutes before we normally wake up. So, for someone who typically rises at 6am, that will be somewhere between 3.30am and 4.30am.

This is the time when light is least likely to occur. When we’re travelling, it can be a different story.

For instance, if someone travels from Paris to Perth and lands at around 10am Perth time, that corresponds to 3am Paris time, when their core body temperature is at its lowest.

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“If a blanket recommendation is followed, and you seek sunlight immediately after arrival, this light exposure will push the clock in the wrong direction, causing it to shift later instead of earlier,” says Dr Dean Miller, a sleep and performance scientist at CQ University. “In effect, you’ve turned a manageable seven-hour advance into a much harder 17-hour delay – prolonging jet lag and making recovery slower.”

The quickest route back to local time, says Miller, would require staying in relative darkness for the first couple of hours after landing until the body is out of the crossover period.

Bring on the sleep

Like light, depending on how we time it, melatonin can help push our body towards the new time, or away from it, thereby prolonging our jet lag.

“It’s essentially timing information,” says Cain.

Specific, inflexible timing information is what many apps and people offering advice get wrong, adds Cain. If we can’t follow that advice perfectly (if we have no control over the light we are exposed to, for instance), then the advice needs to adjust.

“The advice is different depending on where you’re coming from and where you’re going, but even the time of day of your flight,” says Cain. “There are so many moving parts, and you need to understand the underlying mechanisms to get it right.”

Without this understanding, “it’s dumb at its core”, says Cain, who is developing a jet lag app, which will use light sensors and adjust its advice based on the individual.

With melatonin, taking it during the day when our body isn’t naturally releasing it will shift the timing of our clock, just like light.

“If you’re travelling from west to east across six time zones, taking melatonin in the afternoon (in your body’s time) is good because it’ll advance your clock and that’s what you need,” he explains. “But if you took it in the late night or early morning, it delays your clock and can worsen jet lag.”

Eat your way to a new destination

Food and exercise may not shift our central clock, but they also work to 24-hour rhythms and can help align our peripheral clocks, such as in the liver.

“Like light, food acts as a signal to our body to help set our circadian rhythms,” explains Dr Charlotte Gupta, a researcher and chrono-nutritionist at the Appleton Institute. “If we eat at a time when our body isn’t primed to be digesting food, like at night, this can contribute to misaligning our internal rhythms.”

And because our body is less able to digest what we eat, if our clocks are in sleep mode, it can make us feel more sluggish and prone to gastric upsets, common symptoms of jet lag.

Gupta suggests eating (and exercising) in line with our light timing and sticking to light, unprocessed foods while our system adjusts.

“Meal timing on flights is not necessarily designed around the optimal eating timing.”

If it is not the “right” time for our body, a useful strategy can be to avoid eating or pack healthy snacks to delay eating a full meal until the wake period, Gupta says.

As for caffeine, it can help us override a strong sleep drive when we need to remain awake, says Cain. “If it’s going to be difficult to stay up that long and be in lots of light, caffeine can be useful.”

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