Associations between jet lag and cortisol diurnal rhythms after domestic travel.

OBJECTIVE Millions of adults in the United States travel abruptly across time zones each year. Nevertheless, the impact of traveling over relatively short distances (across 3 or fewer time zones) on diurnal patterning of typical physiological response patterns has yet to be studied in a large, epidemiological sample. DESIGN The current research focuses on 764 middle-aged men comparing variations in diurnal cortisol regulation based on number of time zones traveled eastward or westward the day before. MAIN OUTCOME MEASURE Participants provided samples of salivary cortisol at waking, 30-min postwaking, 10 a.m., 3 p.m., and bedtime. RESULTS Eastward travel was associated with a steeper salivary cortisol awakening response (p < .01) and lower peak (PEAK) levels of salivary cortisol the next morning (p < .05). Westward travel was associated with lower peak levels of cortisol the next morning (p < .05). Effect sizes for these differences ranged from Cohen's d = .29 to .47. Differences were not present for 2 days in their home environment. CONCLUSIONS The results provide evidence that traveling across time zones is associated with diurnal cortisol regulation and should be studied further to understand the subsequent impacts on health and well-being in large national samples.