Light relief: the best way to defeat jet lag

Jet lag is the curse of long-distance travel, but there is now an app to help you adjust as rapidly as possible to a new time zone. It tells you when to expose yourself to bright or dim light after you land. This is just one of a number of "hacks" scientists have devised around our body clocks.

Our body and cells tick to a 24-hour rhythm, causing shifts in our body temperature, immune response, athletic performance and even hand-grip strength depending on time. Scientists estimate that about 40 per cent of our genes keep to this circadian (circa dian: “about a day”) schedule .

Light sets our master body clock, and changing the time when we expose ourselves to light can help to reset it.

“We used only three equations to capture the clock, but this allowed us ask what is the best way to adjust to a new time zone,” says Olivia Walch at the University of Michigan, who developed the Entrain app for jet lag. “I expected only my mum and dad to download the app, but it has become really popular.”

A scientific paper solving 1,000 different time scenarios underpins the app.

Average sleep time moves by four minutes every degree east to west, a recent survey revealed. It is down to biology. Our master clock is set by special cells in our eyes with nothing to do with vision. These cells are especially sensitive to blue light and they co-ordinate time for billions of cells.

However, technology can throw a spanner in the works. Smartphones and tablets, for example, emit strongly in blue, so can upset our body clock and sleep schedule. Disobeying our clock and staying up late can lead to “social jet lag”, which can happen when you don’t set your alarm and then sleep late.

The light in our homes and offices is also dimmer than we might think. "We live in dark caves," Prof Russell Foster from the Nuffield Department of Clinical Neurosciences in the UK told the scientific meeting ESOF in Manchester this summer.

“In an office and domestic setting, there’s only 300 to 400 lux, but near a window you might get 3,000 lux, and even in Manchester you get up to 100,000 lux outside.” Natural light trains our clocks better than artificial light.

Still, technology is offering fixes too. The latest Apple iPhones shift their light spectrum as night creeps in to tone down blue. There is also free software called F.lux that will change your computer’s light output as daylight draws to a close [your screen takes on a redder hue]. These may help you sleep better.

It's not trivial: having your clock run to schedule is better for your health. "Light exposure at night has been linked to higher rates of breast and prostate cancer," says Dr Andrew Coogan, chronobiologist at Maynooth University. "The hormone system is strongly under circadian control, and these are hormone- dependent cancers."

In partnership with Connolly Hospital in Dublin, Coogan is studying how social jet lag may put people at risk of diabetes. Already, evidence of bad effects of messing with your biological clock have stacked up: shift work increases your risk of cancers and cardiovascular disease.

Eating, too, has a significant time element. "Our body cannot make and break down fat at the same time. These have to be fine-tuned for time of day. When these rhythms are compromised, it predisposes us to all sorts of diseases," says Prof Satchidananda Panda at the Salk Institute for Biological Studies in California. He says timing can matter more than what the food is.

Indeed, restricting food intake to between 10 and 12 hours a day (rather than, say, 16 hours) leads to increased muscle mass, improved sleep and better overall health, Panda has shown. To help people take up a healthier schedule, his lab designed an app called My Circadian Clock. Users take a quick snap of their food and also record when they sleep and move.

In one of his studies, people who ate to a restricted, more disciplined schedule had molecular flags that suggested lower inflammation. Panda also studies how some people manage shift work better than others.

The apps are being downloaded worldwide, including in Ireland. “I’ve found it amazingly helpful and experienced much less jet lag on trips to Asia,” says Walch.

On the first day of a flight from Dublin to Los Angeles, you should seek as much light as possible until 11.45pm, she advises. On the second day, avoid dark during the morning and afternoon and then seek light until 1.30am. The third day, avoid light until mid-afternoon and then get exposed to as much as possible until 12.30am.

“During the periods when you want to avoid light, it’s not important to be asleep. One can still travel and do things,” says Walsh. “It is just better to limit as much outdoor light as possible until the afternoon those first days.”

This will train you inner clock for roughly a 7am wake-up time in California and 11pm for bed.

HOW OUR BODY CLOCKS INFLUENCE HEALTH
We are more vulnerable to infection by viruses at certain times of the day. This is because our body clock influences the ability of viruses to multiply and spread, a new study has shown.

Mice infected with viruses at the very start of their day experienced 10 times more virus replication than mice infected 10 hours later. This means infection at the wrong time of the day could cause much more acute infection in people, says Prof Akhilesh Reddy, who led the study at the University of Cambridge.

“You are also more susceptible to infection when you mess around with your clock, so that has consequences for people who do shift work, as they may be more prone to viral infections,” Reddy says. The results also help to explain why shift workers are more prone to infection and chronic disease.

His discovery and its relevance for people are supported by recent studies showing that the time of day that a flu vaccine is administered can influence how well the vaccine works. Apps may in future suggest when the optimal time is to administer vaccines or drugs.

The study was published last month in the scientific journal Proceedings of the National of Sciences.