The farther you travel, the harder it is to shake off the sleepiness and fatigue associated with jet lag. No matter how good our intentions, often one good night’s sleep is not enough. More is needed, and it is disheartening not to know how many days it takes to recover from the jet lag.
That state is so common that even the Royal Spanish Academy has accepted the term, though it recommends writing it in italics because it is a loanword. It defines it as ‘the discomfort or disorder caused by a long flight with a large time change’. In scientific terms it is a profound desynchronization between our internal biological clock and the new geographic time.
This phenomenon affects everything from our hormones to our basal metabolism. And, bad news for travelers: its impact on the body lasts longer than we can recover with a single night of sleep.
Bryan Johnson, the traveler who recommends not traveling
“Transoceanic travel has a high physiological cost.” Those are the words of Bryan Johnson, the biohacking guru. This American tech entrepreneur known for his Blueprint project, through which he monitors hundreds of biomarkers to try to slow aging, is used to traveling regularly. And he knows that his body is paying a heavy price for crossing so many time zones and so often.
He arrived at this conclusion after analyzing his own data during trips to China, India, and Australia. And his conclusion is that one should not undertake more than one trip with major time-zone changes per quarter.
The reason, according to him, is that “a single trip requires weeks to recover and long-haul flights are terrible for the body.”
Johnson’s 9-test for the jet lag
As a good longevity guru, Johnson applies his own tests and draws his own conclusions. Experts take them with a grain of salt and remind that those recommendations are not part of the evidence, nor accepted by scientific societies.
Among other conclusions, he suggests that after a trip from Los Angeles to Australia, the jet lag has increased his biological age by about 13 years.
One of the biomarkers he uses is grip strength. “Before the trip it equaled 63 kilograms (grip-strength age equivalent to 48 years). After the trip, (I dropped to) 56.6 kilograms, a grip-age of 61 years,” he explains on the social network X.
Asked by netizens whether this accelerated aging situation due to jet lag is reversible, he responds that “even if the situation normalizes in a few days, the biological cost of traveling is something people are not aware of. We are still waiting for the results of other analyzed parameters.” And he ends with a troubling message: “Data on the biological impact associated with travel reveal a magnitude far greater than most people imagine.”
Tricks to recover faster
As a frequent traveler, Johnson also has his tricks to recover better from the jet lag. And, of course, he shares them on his social networks.
- Fasting. Avoid eating before long flights (sometimes fasting up to 33 hours) to prevent digestive disorders and a poor quality of sleep.
- No caffeine or alcohol. Two substances we know interfere with quality sleep.
- Immediate sleep. As soon as he reaches his seat, he prepares to sleep. This helps him tune to the destination’s nighttime schedule in advance.
- Sensory deprivation. He uses glasses that block blue light, earplugs, and an opaque sleeping mask to sleep without discomfort.
- Gym after landing. As soon as he arrives at the destination, he prefers to do some exercise, expose himself to 20 minutes of natural sunlight without sunglasses, and adapt to the local meal schedule.
- Nutritional supplements. He takes 300 mg of slow-release caffeine in the morning and 3 mg of melatonin before sleep. The aim is to stay awake and facilitate sleep, resynchronizing the circadian clock more quickly.
What science says about jumping time zones
Being prudent about Johnson’s eccentricities, it is true that the most evident impact of crossing five or more time zones is the disruption of rest. The classic rule guiding experts says that our body needs, approximately, one day of recovery for each time zone crossed. This means that a trip from Madrid to New York (6 hours difference) or to Punta Cana (6 hours) could require almost a week for the biological clock to re-synchronize.
If the destination is even farther and keeps the same time year-round, such as Tokyo (8 hours difference in summer and 7 in winter), Beijing (6 hours in summer and 7 in winter) or Sydney (8 hours in summer for Europe and up to 10 in winter), the process can prolong even more.
It’s harder to recover if we travel east
Recent research shows that recovery is not a process that is as linear or uniform. A comprehensive study conducted by researchers at the Center for Sleep and Cognition of the National University of Singapore, which analyzed more than 60,000 travelers and logged a total of 1.5 million nights using smart devices (Oura rings), yielded revealing data about the architecture of our rest.
The results indicated that, while the total duration of sleep typically normalizes in just 2 days, the structure of sleep and the circadian schedule take much longer to adjust. The direction of travel —whether we fly east or west relative to our usual location— also influences.
After a trip east — for example, returning to Spain from Japan, South Korea or Australia, where the day begins earlier— the body may need more than a week to recover deep and truly restorative sleep. Westward trips, such as vacations in New York, Mexico or the Caribbean, tend to be somewhat easier to tolerate, since the body finds it less difficult to lengthen the day than to shorten it.
Not everyone adapts the same
There are people who cope with jet lag better and others for whom it takes quite a bit longer. This is because the speed of adjustment to the schedules depends on the hypothalamus’s ability to adapt to new rhythms.
“This process is markedly variable between individuals and seems to depend on genetic predisposition, chronotype (people who perform better in the morning or in the afternoon) or the correct use of zeitgebers or biological synchronizers, such as strategic use of natural morning light,” explains Fernando Hernández Olmeda, physician specializing in endocrinology and nutrition at the Institute of Advanced Medicine and Dermatology (IMDA).
The 4/10/120 Rule
As a good friend of monitoring and quantifying everything, Bryan Johnson states his own rule for dealing with jet lag. It is the 4/10/120 rule, something like the gold standard of the days needed to recover from jet lag. “It applies when there is a time difference of more than 4 hours. Trips of that type should be limited to fewer than 10 days per month and at most 120 days per year,” he explains.
His suggestion is that “you must give the biological clock about 9 or 10 nights of proper alignment after each major time-zone change. In addition, you should keep the total days of mismatch under 10 per month to avoid entering the biological ‘red zone’.”
The adjustment in days, according to Bryan Johnson
From his studies, he explains that “nine days of restorative sleep are needed to recalibrate metabolic control and blood glucose, as well as for the resynchronization of the circadian rhythm”. Regarding sleep duration, he adds that “two days are needed for sleep duration to return to within about 12 minutes of baseline values. However, changes in timing and the architecture of sleep did not recover baseline levels until after 15 days.
“Dicho de otro modo: aunque uno pueda sentirse descansado después de un par de noches, el reloj biológico sigue desajustado durante bastante más de una semana. Por eso mismo, realizar viajes con una separación inferior a dos semanas mantiene al organismo en un estado de desincronía permanente”, explica la biohacker.
And not only does it affect sleep
Mood is also affected by the time shift. “Those who travel 21 or more nights per month have between 1.7 and 3.7 times more likely to test positive on anxiety, depression, alcohol dependence, smoking, and poor sleep quality, compared with those who travel between 1 and 6 nights per month.”
To complete the list of dangers for the traveler, “the risk of deep venous thromboembolism triples when flight time exceeds 12 hours within a 4-week period,” he notes. In short, it is not only the days needed to recover from the jet lag. Traveling far leaves a mark on the body and should not be overlooked.
