Frequent flyers have a bag of tricks to get over jetlag. Scientists have plenty of suggestions too: from getting a dose of sunlight, melatonin or a hit of exercise, to staying hydrated, skipping caffeine, and eating at local meal times.
While none are guaranteed quick fixes, these tips help our bodies slide back into their usual circadian rhythms which course through every organ of the body, controlled by a 'master clock' in the brain.
Now, a team of US researchers modeling those circadian rhythms has landed on what they say is the fastest way to shake off jetlag and reset your body clock – a strategy that could apply to groggy shift workers too.
"Having a larger meal in the early morning of the new time zone can help overcome jet lag," says applied mathematician Yitong Huang of Northwestern University in Illinois, who led the modeling study.
"Constantly shifting meal schedules or having a meal at night is discouraged, as it can lead to misalignment between internal clocks."
The findings echo earlier studies on meal timing, but also extend our understanding of why circadian rhythms tire with age.
Huang and colleagues modeled circadian rhythms using a suite of mathematical equations, a rough approximation of the human body at best, so they could analyze multiple circadian clocks and cues at once, including light exposure and food intake.
Previous studies either zoomed in on cyclic molecular interactions between proteins within cells, or zoomed out to study the activity of the suprachiasmatic nucleus (SCN), the central circadian clock in the brain which sets the daily tempo of our lives.
Huang and colleagues' model included both this central circadian clock and peripheral circadian clocks, which exist in nearly every other organ of the body. Unlike the central circadian clock, which responds to light, timing of the peripheral clocks is cued by patterns of feeding and fasting.
Their model was simple enough to compute, yet "sophisticated enough to capture many intriguing features of the real circadian clocks, such as the east-west asymmetry of circadian response to jet lag," Huang and colleagues write in their paper.
Of particular interest to the researchers were the effects of aging on circadian rhythms. Older folks generally take longer to recover from jetlag, which might be because their circadian rhythms are more easily disrupted or take longer to regroup.
Huang and colleagues' findings reaffirm what has been suggested before from animal studies, about the way circadian rhythms slump with age.
Weaker signals from the aging brain's SCN led to the body's peripheral clocks becoming disorganized, and those clocks took longer to recover from a 6-hour time shift akin to long-distance travel. Reduced sensitivity to light had a similar effect.
As for food, the teams' modeling suggests a large, single meal in the early morning for three days can help realign our body clocks after jetlag.
"These results highlight the importance of peripheral clocks in regulating the circadian rhythm and provide fresh insights into the complex interplay between aging and the resilience of the circadian system," Huang and colleagues write.
Finding ways to keep our body clocks in sync and ultimately improve sleep is vitally important in aging populations.
Circadian rhythm disturbances and sleep-cycle disruptions have been linked to the build-up of proteins of Alzheimer's disease that our brain usually clears as we snooze.
Researchers are also exploring whether intermittent fasting could help adults sleep better and slow Alzheimer's disease, by resetting circadian clocks that go awry in the disease.
The study has been published in Chaos.