Frequent travellers often insist that flying east causes worse jetlag than flying west. And, despite those who may dismiss the notion, a new study suggests that they are right.
A group of scientists from the University of Maryland produced mathematical models to show why this might be.
Jetlag is believed to be caused by the disruption of our body clocks – the circadian rhythm.
According to the study, this cycle, on average, runs over a little more than a day – about 24.5 hours. As flying west, in the same direction as the rotation of the Earth, lengthens the day slightly, it is more in tune with our body’s cycle than flying east, which shortens the day.
That may also explain why some people are affected more or less severely by jetlag than others, the study, published in the journal Chaos, says, as individual circadian rhythms can be longer or shorter than the typical 24.5 hours.
The circadian rhythm itself is regulated by a clump of brain cells known as the suprachiasmatic nucleus, controlled by exposure to light.
When travelling by air, changes to the available light are thrown out of kilter, resulting in jetlag. So the researchers developed a mathematical model to simulate what happens to these brain cells when this happens.
This showed the microscopic dynamics of individual pacemaker cells in the suprachiasmatic nucleus and found that not all cells adjust to a new time zone at the same rate, but as a group arrive at the same result about the same time.
“Our model explores what would happen to an individual if he/she were suddenly taken from one time zone and dropped in another,” lead author Michelle Girvan was quoted by Gizmodo as saying.
“The important 30-minute difference that comes into play is that the natural frequency of [the brain cells] is about 30 minutes longer than 24 hours.”
The study calculated that, with the average circadian cycle of 24.5 hours, it would take a person just under four days to recover from a trip in which they passed westward through three time zones. But it would take just over four days after travelling east.