Exploring far-flung destinations can bring a wealth of novel experiences, but the jet lag that comes with it can have unpleasant side effects. Adjusting to a different time zone often brings with it fatigue, sleep issues, and a variety of issues that can overshadow the excitement of a new adventure.

Jet lag is caused by differences between the circadian system (the body's internal clock) and the surrounding environment. Around the turn of this century, scientists began to realize that the human body has multiple internal clocks that are calibrated in different ways, and when these clocks are out of sync with each other, symptoms like jet lag can occur. This condition can occur in a variety of ways and becomes increasingly common as we age.

In the book "Chaos" published by AIP Press, a team of scientists from Northwestern University and the Santa Fe Institute developed a theoretical model to study the interaction between multiple internal clocks under the influence of disturbances such as aging and jet lag.

Modern research shows that the circadian clock is present in nearly every cell and tissue in the human body. Each clock relies on its own set of cues to calibrate; for example, the brain's clock relies on sunlight, while peripheral organs calibrate around mealtimes.

Author Huang Yitong said: "Conflicting signals, such as warm weather during short light periods or nighttime eating - eating when the brain is about to rest - can confuse internal clocks and cause them to become desynchronized.

Currently, little is known about how the body's various internal clocks interact with each other. The complexity of considering multiple clocks means researchers tend to use simplified models.

Schematic diagram of mathematical model. The model consists of two sets of coupled oscillators, one representing the central clock in the brain, which is affected by light, and the other representing the peripheral clock, which is affected by food. Image source: Huang et al.

"Most studies have focused on a specific time cue or a single clock," Huang said. "Important gaps remain in our understanding of the synchronization of multiple clocks under conflicting timing cues."

Huang and her colleagues took a different approach, developing a mathematical framework to explain this complex interaction between systems. Their model has two coupled oscillator groups that mimic the natural rhythm of the circadian cycle. Each oscillator affects the others while adjusting based on unique external cues.

Using this model, the team was able to explore how this coupled system is disrupted and what causes the effects to worsen. They found that common symptoms of aging, such as weakened signals between circadian clocks and reduced sensitivity to light, make the system more susceptible to disturbances and slower to recover.

They also found a new way to speed up recovery from jet lag and similar disruptions. According to their findings, the way to improve sleep is through the stomach.

"Eating an extra meal early in the morning in the new time zone can help overcome jet lag," Huang said. "Continuously changing meal times or eating in the evening are discouraged as this can cause the body's clocks to be inconsistent."

The authors plan to look at the other side of the equation and identify factors that make internal clocks more resilient. These findings may lead to recommendations to prevent jet lag in the first place or to keep the circadian system healthy into old age.