What jet lag really does to your body

Every month, Cloe Cheer, 24, takes six flights on average to accommodate her busy work schedule. In the spring, she travelled to Chicago, Munich, Tokyo and Sydney in the space of just six weeks.

"I work in event planning, and my job takes me all around the world. It's exciting but also very demanding. Flying across so many time zones in such a short time means I am often jet-lagged and sleep deprived," she says.

Recently, Cheer had to seek medical help as this lifestyle had taken a toll on her body.

"I was constantly exhausted. I'd started to gain weight. I developed high cholesterol. The doctors had to give me a strict diet to follow to improve my health," she explains.

Although her dietary patterns and the stress of her work may have been to blame, some of her health issues may also be linked to the frequent jet lag she deals with.

After years of research, it is now clear that jet lag is not just a phenomenon which affects people's concentration or quality of sleep. It may have serious physical impacts, especially for those who experience it regularly, such as frequent business travellers or aircrews.

What is jet lag?

The human body works on a 24-hour cycle, alternating between periods of sleep and alertness at regular intervals. Known as circadian rhythms, these cycles are regulated by an internal 'clock' in the brain.

When we travel to a new time zone, our circadian rhythms take several days to adjust. This phenomenon is what we call jet lag, characterised by a disruption of sleep and impaired daytime functioning.

"Often, people confuse jet lag's effects with the effects of flying. It's just a desynchronisation of body clocks due to moving from one place to another. But being dehydrated when you arrive is a consequence of having been on the plane for a long time," sleep expert Neil Stanley says.

Health problems linked to jet lag

Beyond the disturbances to sleep and daytime functioning, travelling across time zones can lead to a number of other short-term health issues. They tend not to be too serious, but can be uncomfortable and even ruin a holiday.

Stomach problems

The most common complaints include stomach problems and cravings for foods at odd hours. People get hungry at the times they usually eat, which might be in the middle of the night in their new time zone. Feeding cycles are disrupted, and so is digestion.

"People are forced to try to sleep when their body is geared up for being awake; they try to stay awake when their body is trying to make them sleep, and they eat when the digestive system is not ready for a meal," explains Charmane Eastman, professor in the Biological Rhythms Research Lab at Rush University in the USA.

Irregular periods

It's also quite common for women to see an impact on the timing of their menstrual cycles.

"I have noticed that periods are often delayed," Cheer says.

And for those who are taking oral contraception - or any other drugs - switching to the schedule of the new time zone may be a source of complications.

"People on medications that must be taken at certain times of day might end up taking them at the wrong times for their body if they don't shift their circadian clocks to the destination time zone," warns Eastman.

Long-term consequences

People who do not fly frequently are unlikely to develop more serious chronic physical problems as a result of jet lag.

But studies involving flight crews or shift workers have documented the debilitating physical health effects of repeated jet lag. The risk of gaining weight and of developing metabolic conditions like type 2 diabetes seems to be heightened.

"Historically, we thought that there wasn't much difference between how metabolism functioned at night and during the day. Now, we know that's not the case," reveals Dr Vikki Revell, who studies circadian rhythms at the University of Surrey.

Other studies have suggested that flight attendants also have higher rates of cancer (especially breast cancer and melanoma). Researchers are unsure why this is. It's possible that repeated exposure to cosmic radiations while flying is to blame, but animal studies have hinted that chronic jet lag may be as important to understand this cancer risk. Mice who are put in a situation of jet lag indeed appear to develop cancerous cells faster.

It is also possible that chronic jet lag accelerates cognitive decline. In one study, scientists found that among staff working on international flights, those who had been in the job longer scored worse on memory tests.

While more research needs to be carried out to assess the link between chronic jet lag and these conditions, the evidence is slowly starting to accumulate.

Tips to deal with jet lag

To make the most of your time abroad and reduce the negative effects of jet lag to a minimum, a couple of steps can easily be taken.

Adapt your sleep schedule before the flight

You can already do part of the work before you leave the country by gradually changing your sleep schedule. If you are travelling east, gradually going to bed earlier each day before the flight can help. If flying west, it will be most effective to delay sleep.

Light and melatonin

But you can't easily change the time you fall asleep and wake up without also changing your light/dark cycle. Exposure to light (whether sunshine or intermittent bright light from light boxes) at appropriate hours and taking melatonin medication can thus help shift your body clock and your bedtime to match that of the time zone you are travelling to. It can help you change your sleep schedule before the flight.

"When flying east, if people start to find it difficult to fall asleep as early as scheduled and find it difficult to wake up when scheduled, then it means their circadian clock is not advancing as much as their sleep schedule, so they need more bright light in the morning or less bright light before bed," Eastman points out.

"When preparing to fly west, if they start to find it difficult to stay awake until bedtime and wake up earlier than scheduled, they need more bright light before bed or less bright light after waking up," she adds.

Change your watch and make the most of the flight

As soon as you get on the plane, change your watch to match the time at destination so that you are mentally prepared, and can start adapting to your new schedule.

"You should start the new routine as soon as you get on the aircraft, moving your watch and treating your flight as a normal day. If you are flying by day, keep the blinds open and stay awake. If it's night at your destination, try to get to sleep as soon as possible," Stanley says.

Maximise your chances of going to sleep at the correct time

Avoid alcohol or caffeine before bedtime: both of these can make sleep more difficult and disrupt your body clock even more. Also, try not to take long naps in the middle of the day, and use earplugs and blindfolds to improve the quality of your sleep when it's actually time to go to bed.

Sleeping more hours on the plane or taking sleeping pills can help reduce the negative effects of sleep deprivation but it does not treat the underlying cause of jet lag.

"The ability to sleep on the plane can reduce the sleep deprivation that makes jet lag worse. But this is not enough to eliminate jet lag. For that, you have to wait until your sluggish circadian clock slowly adjusts to the new time zone," Eastman concludes.