Why jet lag can be worse when you travel east

The Myanmar Times - - The Pulse -

HU­MANS have been fight­ing jet lag for some 50 years. In that time we’ve cast far and wide for tricks to re­jig­ger sleep cy­cles dis­rupted by air­planes. There are du­bi­ous herbal sup­ple­ments and, more du­bi­ously, ear­buds that blast light to­ward the brain. Sleep ex­perts sug­gest soak­ing up finely por­tioned amounts of sun­light, with more light early in the east and wait­ing un­til later in the west. For the des­per­ate, a perky cof­fee or sleep-in­duc­ing beer can be a tempt­ing – al­though not al­ways ad­vis­able – op­tion.

One folk ob­ser­va­tion, how­ever, seems to ring true. As fre­quent cross­con­ti­nen­tal travellers might al­ready sus­pect, it is gen­er­ally tougher to ad­just when trav­el­ling east. Go west, on the other hand, and rest a lit­tle eas­ier.

That’s be­cause our sleep cy­cles need dif­fer­ent amounts of time to read­just. It is eas­ier, say sci­en­tists at the Univer­sity of Mary­land, for our neu­rons to cope with a pro­longed day than a short­ened one. Trav­el­ling west – back­ward in time zones – adds hours to the day, closer to the longer day most hu­man bod­ies nat­u­rally pre­fer.

Our bod­ies’ sleep cy­cles are ruled by neu­rons that act like pace­mak­ers. But for those neu­rons to stay syn­chro­nised, we must be ex­posed to light, akin to wind­ing a slow clock. When we travel, that tun­ing pe­riod falls apart.

Writ­ing in the jour­nal Chaos this month, the re­searchers math­e­mat­i­cally mod­elled brain cells that con­trol sleep, to bet­ter un­der­stand why trav­el­ling to eastern time zones may pro­duce rougher bouts of jet lag.

To show this, the sci­en­tists cre­ated a sim­pli­fied model of the area of the brain called the suprachi­as­matic nu­cleus. This is the clus­ter of neu­rons that reg­u­lates the cir­ca­dian rhythm. That rhythm, or in­ter­nal clock, kicks us awake and will later tell us it’s time to sleep. Each of us has rhythm that re­peats roughly ev­ery 24 hours, with an ebb and flow of sleep hor­mones.

Cru­cially, cir­ca­dian rhythms are not per­fectly at­tuned with the hu­man ideal of ex­actly 24 hours. On av­er­age, cir­ca­dian rhythms last a lit­tle bit longer – about 24.5 hours.

“Our model sug­gests that the dif­fer­ence be­tween a per­son’s nat­u­ral pe­riod and 24 hours con­trols how they ex­pe­ri­ence jet lag,” Michelle Gir­van, a physics pro­fes­sor at the Univer­sity of Mary­land, said in a state­ment.

In the study, Gir­van and her col­leagues sent fic­tional travellers on trips around the world, cross­ing in­creas­ing num­bers of time zones. Those av­er­age ex­tra 30 min­utes on the clock seem to make a large dif­fer­ence, they found, in mak­ing western trips eas­ier on the brain.

The sci­en­tists mapped out how long it would take for their model brains to re­cover from in­creas­ingly dis­tant trips. That is, their model was a syn­the­sis of all the neu­rons that in­di­vid­u­ally spin through a daily cy­cle. For peo­ple suf­fer­ing from jet lag, the neu­rons pop out of sync. The re­sult is like a row of watches all show­ing slightly dif­fer­ent times. As we re­cover, the neu­rons start to show the same time again.

Trav­el­ling west over six time zones re­quires an av­er­age of about six days to fully re­cover, based on the model, whereas trav­el­ling east jumps up to eight days. At nine time zones crossed, the dif­fer­ence is even starker: about eight days to re­cover from a western trip, but 12 days from an east­bound one.

This study is sup­ported by ear­lier re­search into what we know about the in­ter­play be­tween light and the cir­ca­dian rhythm, as light is the main mech­a­nism that rewinds the bi­o­log­i­cal clock. Our anatomy re­flects this, too. The nerve fi­bres that link the eyes and brain thread right below the suprachi­as­matic nu­cleus.

When travellers head east, hours are lopped off from the day – and the amount of sun­light avail­able – which means we want to stay awake longer in the dark. Con­versely, head­ing west pro­longs the day, which may bet­ter com­ple­ment our in­ter­nal clocks.

Im­por­tantly, not all in­ter­nal clocks tick at the same rate. That varies, ex­plained Gir­van, de­pend­ing on the per­son. “Some peo­ple may have a nat­u­ral cir­ca­dian rhythm with a pe­riod of 24.5 hours,” she said, “while oth­ers may have longer or shorter nat­u­ral rhythms.” Vari­a­tions among our in­ter­nal clocks are thought to be why jet lag af­fects some peo­ple more than oth­ers.

Gir­van hopes this re­search can lead to bet­ter fixes for out-of-whack cir­ca­dian rhythms, whether they arise from “rapid cross-time-zone travel, shift work, or blind­ness”.

– The Wash­ing­ton Post

Photo: Shutterstock

Fly­ing into the sun­set? You’ll be aaal­l­l­ll­ri­i­i­ight.

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