East vs. West: Why Jet Lag Direction Matters

Frequent travelers often report a common experience: jet lag feels significantly more brutal when flying east compared to flying west. This isn't just a feeling; it's a well-documented phenomenon rooted in the fundamental biology of our internal clocks.

The Verdict: East is the Beast

For the vast majority of people, jet lag is worse when traveling east. A flight from New York to Paris will typically cause more severe symptoms than a flight from Paris to New York.

The Science: Your Body's Natural Rhythm

The reason lies in the natural length of our internal body clock, or circadian rhythm. While we operate on a 24-hour day, studies have shown that the average human circadian rhythm is slightly longer than 24 hours (around 24.2 hours, on average).

This means our bodies have a natural, built-in tendency to want to delay our schedule—to stay up a little later and wake up a little later.

Phase Delay vs. Phase Advance

Traveling West: The Easier "Phase Delay"

When you travel west (e.g., from London to Los Angeles), you are moving to an earlier time zone. To adapt, you need to stay up later and wake up later. This is called a "phase delay." Since your body's clock naturally wants to drift later anyway, this is a relatively easy adjustment. You are working with your body's natural tendency.

Traveling East: The Difficult "Phase Advance"

When you travel east (e.g., from Los Angeles to London), you are moving to a later time zone. To adapt, you must force yourself to sleep earlier and wake up earlier than your body wants to. This is called a "phase advance." You are working directly against your body's natural tendency to delay, which requires a much greater effort to reset your clock.

How to Manage the Eastbound Struggle

Because traveling east is harder, it requires a more disciplined approach to management:

  • Pre-Adjust Your Schedule: Start going to bed and waking up 30-60 minutes earlier for a few days before your eastward flight.
  • Morning Sunlight is Crucial: Upon arrival, get as much bright sunlight as you can in the morning. This is the most powerful signal to advance your clock.
  • Avoid Evening Light: Dim the lights and avoid screens for 2-3 hours before your new, earlier bedtime.
  • Consider Melatonin: A low dose of melatonin can be particularly helpful for eastward travel to signal sleep onset at an earlier time (always consult a doctor).