The late-year summit calendar puts many delegates, executives and journalists on long-haul flights in quick succession. The UN climate conference, COP31, runs in Antalya, Türkiye, from November 9 to 20, 2026, and the G20 Leaders’ Summit follows in Miami on December 14 and 15. The CDC Yellow Book, the federal reference on health for international travel, devotes a chapter in its 2026 edition to jet lag and how to manage it.
The chapter describes jet lag disorder as a sleep disorder caused by rapid travel across time zones, which leaves the body’s internal clock out of step with local time. Symptoms can include disturbed sleep, daytime sleepiness, impaired thinking, general malaise and digestive problems. The chapter cites one survey in which 68% of international business travelers reported negative symptoms on a regular basis.
Why direction matters
According to the CDC, most people find it easier to shift their body clock later than earlier, because the natural internal cycle runs slightly longer than 24 hours. As a result, adapting after westward travel takes place at an average of about 1.5 hours a day, compared with about 1 hour a day after eastward travel. Travelers flying east, such as from the Americas to Antalya, need to move their clock earlier. Those flying west, such as from Europe to Miami, need to move it later.
Before and during the flight
The guidance suggests choosing a flight that arrives at a time that allows well-timed exposure to light. Where possible, travelers can shift their sleep toward the destination schedule in the two to three days before departure, by about one hour a day: later for westward trips and earlier for eastward ones. Jet lag calculators can help plan the timing of light, sleep, caffeine and melatonin.
On board, the CDC advises timing meals, sleep and light exposure to the destination time zone, staying hydrated, avoiding excess alcohol and avoiding sedative medications with long half-lives. It notes that alcohol and caffeine can both disrupt sleep and contribute to dehydration.
On arrival
At the destination, the guidance recommends maximizing natural light exposure and staying awake during the local day. Short naps of 20 to 30 minutes can help sustain alertness, while longer naps may make it harder to sleep at night. Bright light in the morning generally helps shift the body clock earlier, and light in the evening helps shift it later.
The chapter also covers timed melatonin. It says doses of 0.5 to 1 mg are often enough to shift the body clock, that high doses above 5 mg are not recommended, and that taking melatonin at the wrong time can make the mismatch worse. It notes that melatonin is not regulated by the Food and Drug Administration, so the amount in a product may differ from the label. The guidance is written for health care providers, and travelers considering melatonin or sleep medication should discuss it with a clinician before they travel.
