Jet lag

What is jet lag?

Jet lag is a temporary sleep disorder that occurs when you travel quickly across multiple time zones. Your body has an internal clock called circadian rhythms that regulates when you feel awake and when you feel sleepy. When you cross time zones, your internal clock remains synced to your home time while the external environment shifts to a new schedule. This mismatch causes the symptoms we call jet lag ^[1].

Why jet lag happens

The circadian system is controlled by a small region in your brain called the suprachiasmatic nucleus. This master clock coordinates with peripheral clocks in your liver, digestive system, and muscles. When you travel across three or more time zones within hours, these clocks fall out of sync with each other and with the local light-dark cycle ^[2].

The severity depends on how many time zones you cross and which direction you fly. Eastward travel typically causes worse symptoms than westward travel. This happens because the human circadian clock naturally runs slightly longer than 24 hours, making it easier to stay up later than to fall asleep earlier ^[3].

Common symptoms

Jet lag affects multiple body systems. You may experience difficulty falling asleep at night or waking up too early in the morning. Daytime fatigue and sleepiness are common, along with problems concentrating and making decisions. Many travelers report irritability and mood changes. Digestive issues such as nausea, constipation, or loss of appetite frequently occur. Some people also experience headaches and a general feeling of being unwell ^[1].

How long jet lag lasts

Recovery typically takes about one day per time zone crossed. A flight across six time zones may require up to six days for full adjustment. However, individual variation is substantial. Age, light exposure habits, and preparation before travel can shorten or extend this timeline ^[3].

Evidence-based strategies for relief

Strategic light exposure

Light is the most powerful tool for resetting your circadian clock. After flying east, seek bright morning sunlight and avoid bright light in the evening. After flying west, get evening light exposure and limit morning brightness ^[2]. Light boxes producing 5,000 to 10,000 lux can help when natural sunlight is unavailable.

Melatonin supplementation

Melatonin is one of the most effective interventions for jet lag. A Cochrane review of ten randomized trials found that taking 0.5 to 5 mg of melatonin near bedtime at your destination significantly reduces symptoms. The number needed to treat is just 2, meaning one in every two people benefits ^[4]. Timing matters: take it 30 minutes before your desired bedtime in the new time zone. Avoid taking melatonin at the wrong time, as this can worsen symptoms.

Meal timing

When you eat affects your peripheral body clocks. Start eating according to your destination schedule as soon as possible. Research shows that breakfast timing is particularly important for resetting these clocks. Keep meals within a 10 to 12 hour window aligned with the local day ^[5].

Pre-travel preparation

Begin adjusting your schedule two to three days before departure. For eastward trips, go to bed and wake up one to two hours earlier each day. For westward trips, shift later. Combine this with timed light exposure to support the adjustment ^[2].