Biology and lifestyle play a role in determining the severity of jet lag, but preparing in advance can help adapt quicker.Frequent travelers, take note. Long flights across multiple time zones can take a toll on the body, often resulting in jet lag. S. Justin Thomas, Ph.D., a sleep expert from the University of Alabama at Birmingham, explains the causes of jet lag and how travelers can minimize its effects.
Jet lag occurs when someone travels to a new time zone and experiences sleepiness or insomnia at unexpected times. Because the human body can adjust only so quickly, it takes time to adapt to a new schedule.
In biological terms, jet lag is a circadian rhythm sleep-wake disorder. It results from a mismatch between the environment and the body’s internal circadian clock, which regulates sleep and wake patterns on a roughly 24-hour cycle, even in the absence of light.
Thomas describes the concept using travel from Birmingham, Alabama, to Paris, France.
“If you are in Birmingham, your circadian phase is probably telling you to go to sleep around 10 p.m. Birmingham time,” said Thomas, an associate professor of psychiatry in Marnix E. Heersink School of Medicine and director of the Behavioral Sleep Medicine Clinic and Training Program. “When it is 11 p.m. in Atlanta, it is 5 a.m. in Paris. If you fly to Paris, your body’s clock is still operating on Birmingham time. This can cause you not to feel sleepy when it’s time to sleep, or to feel sleepy when it’s time to be awake.”
A common misconception about jet lag is that it can be easily avoided by sleeping on the plane or taking medication.
“Because jet lag is a circadian issue, assuming that non-circadian approaches like taking something to sleep on the plane will prevent jet lag is the biggest myth,” Thomas said. “Simply understanding the reason for jet lag is one of the most important things for people.”
Clinically, jet lag cannot be diagnosed unless a traveler crosses at least two time zones, though some people report symptoms even after crossing just one.
“Where someone falls within a time zone can make a difference,” Thomas explained. “The Central time zone, for example, is quite wide, stretching from the Alabama-Georgia border to West Texas.”
Preparation strategies depend heavily on the direction of travel.
“When flying east, travelers should shift their sleep schedule earlier. When flying west, they should do the opposite,” Thomas said.
How early travelers should start adjusting depends on how many time zones they are crossing. The body typically takes about one day per time zone to fully adjust.
“If someone is flying from Atlanta to Paris, they are crossing six time zones, and it can take up to six days for their circadian phase to fully shift from Atlanta time to Paris time,” Thomas said. “Ideally, that means starting adjustments four to six days in advance.”
To help prepare, Thomas recommends gradually shifting sleep schedules before departure.
“Travelers can aim to adjust bedtime by about an hour each day. They can also do smaller increments if it is easier, but that would make the adjustment slower,” Thomas said.
Light exposure is critical because it is the strongest signal for the body’s circadian system.
“Being thoughtful about when and how much light one is exposed to can significantly influence adjustment. In some cases, low-dose melatonin may help facilitate the shift, but it is not necessary.”
According to Thomas, both biology and lifestyle play a role. Maintaining healthy sleep habits year-round and planning can dramatically reduce the severity of jet lag, while poor sleep routines coupled with a lack of preparation can make travel more challenging.