Advancing circadian rhythms before eastward flight: a strategy to prevent or reduce jet lag.
Level 3 - non-randomized controlled study
Controlled comparative trial with non-specified allocation method
PubMed 15700719 · doi:10.1093/sleep/28.1.33
What was done
Twenty-six young healthy adults (11 men, 15 women, aged 22–36 years) underwent a 3-day laboratory protocol following home baseline tracking. Participants were assigned to advance their sleep schedule by either 1 hour per day or 2 hours per day, combined with intermittent morning bright light exposure (alternating 30 minutes at ~5000 lux and 30 minutes at <60 lux for 3.5 hours). Circadian phase shift was assessed by measuring dim light melatonin onset (DLMO) before and after treatment, alongside wrist actigraphy, daily sleep logs, and symptom questionnaires.
What was found
DLMO advanced by a median of 1.9 hours (mean 1.8 hours) in the 2-hour/day group and a median of 1.4 hours (mean 1.5 hours) in the 1-hour/day group; the difference between group means was not statistically significant. By day 3, subjects in the 2-hour/day group developed circadian misalignment and difficulty falling asleep, whereas the 1-hour/day group did not. The 2-hour/day group scored slightly better on symptom questionnaires, but sleep disruption and side effects were minimal overall.
Why it matters
A 3-day pre-travel regimen combining morning bright light with a 1-hour daily sleep advance shifts circadian phase by approximately 1.5 hours without causing the sleep-onset insomnia observed with a faster 2-hour daily advance.
Limits
The sample size was small (n = 26), and the abstract does not state whether group allocation was randomized. The study was conducted in a laboratory simulation without evaluating actual post-flight jet lag symptoms following real eastward travel.
Cited by
- supports It takes nearly two days for the human circadian clock to adjust to a two-hour change in sleep or wake-up time.