Jet lag is a discomfort many of us will have experienced in the days following a long-haul flight across time zones. Mathematicians in the US may have a jet-lag cure in the form a new app called Entrain. But does it work?
Our circadian clock, which drives daily 24-hour rhythms in our physiology and behaviour, is to blame for jet lag. It cannot instantly reset to the destination time zone and the adjusting process can take a number of days. The rate at which our clocks reset depends upon a number of factors including the number of time zones crossed, the direction of travel (east or west) and the light exposure experienced before and upon arrival.
The aspect of jet lag that affects us most is the disruption it causes to our sleep. We can experience problems both falling and staying asleep, as well as waking up when we need to, such that our sleep tends to be short in duration and poor in quality. This then negatively affects our daytime levels of alertness and ability to perform cognitive and physical tasks.
The power of light
Light is the most effective stimulus for altering the timing of our circadian clock and synchronising it appropriately to the local light/dark cycle and desired wake/sleep schedule. By exposing yourself to light at appropriate times of day, it is possible to trick your body into adjusting to the right rhythm and minimise the occurrence, duration and impact of jet lag.
The reference point for light exposure is the time that your body temperature is at its lowest – this normally occurs about two hours before you wake up. Exposure to light before this point will push your clock later in time (required when flying westwards) whereas light after your lowest temperature time will bring your clock earlier in time (required for eastwards travel).
One method of adaptation to the new time zone is to gradually adjust your body clock to the destination time zone before you fly by progressively altering your sleeping patterns and using bright light in the days before your trip. If pre-adjustment is not possible (or convenient), then you can help your clock adapt upon arrival by scheduling your exposure to light and dark. Trying to calculate a light/dark schedule, and adjust this as your clock adapts, around your work or holiday plans can be a bit of a headache. This is where the app may be able to help.
Training your body clock
The Entrain app, developed at the University of Michigan, uses mathematical models to calculate the most effective way of adapting to a new time zone for you. It generates a customised schedule of light and darkness to be followed upon arrival on the basis of information you provide about your light exposure history, typical sleep schedule at home and your itinerary, in terms of expected time indoors and outdoors, while away. If you deviate from the planned schedule then you can just tell the app and it will revise prescriptions accordingly.
The researchers state that instead of gradually shifting the clock to the required time zone, their app will rapidly push our clocks to where it needs to be – faster than the one hour per day that has been the general consensus in the field. The authors state that continuous light has the most impact on the body’s circadian system and that simply adjusting the time of dawn and dusk through exposing our bodies to light is both practical, easy to follow and efficient. This is very different to current advice which schedules bright light for short periods relative to your lowest body temperature point.
Speeding up the rate of adaptation to a new time zone is clearly advantageous. But, although these schedules are mathematically proven, they now need real human data to support them. The models appear to be primarily based on data obtained in the highly controlled, artificial environment of a laboratory, and it will be interesting to see how these translate to the real world.
It is also unclear whether the app takes into account the fact that every cell of the body has its own circadian clock co-ordinated by the master circadian clock in our brains. Following travel across time zones, many of the biological disturbances we experience from jet lag are due to the clocks in our various organs and tissues re-synchronising at different rates. Thus, the app may rapidly synchronise your brain clock but your physiology may be lagging behind so you may still suffer certain symptoms of jet lag due to this internal dissociation.
As the public starts to use this app they will provide the necessary feedback that will be crucial for validating the mathematical models used. Users can submit their data to the app’s creators at the University of Michigan, along with feedback about their jet lag symptoms, in order to build better models that may accelerate the process of overcoming jet lag.