Resynchronization of hormonal rhythms after an eastbound flight in humans:effects of slow-release caffeine and melatonin

The aim of this work was to investigate the potential chronobiotic properti es of slow-release caffeine, in comparison with melatonin, on resynchroniza tion of endogenous melatonin and cortisol secretions after an eastbound fli ght by jet incurring a time loss of 7 h. A group of 27 reservists of the US Air Force received either slow-release caffeine (300 mg), melatonin (5 mg) or placebo before, during and/or after the transmeridian flight. Saliva an d urine were sampled before the flight in the United States (from day -2 to day 0) and after the flight in France (from day I to day 10). Saliva was c ollected once a day,on waking to determine saliva melatonin and cortisol co ncentrations. In addition, concentrations of caffeine in saliva were determ ined three times a day and of 6-sulphatoxymelatonin in urine collected over night to check that the treatment regimes had been complied with. From day 3 to day 5, post-flight saliva melatonin concentrations were significantly different from control values in the placebo group only. During treatment w ith melatonin, the mean urinary 6-sulphatoxymelatonin concentration in the melatonin group was more than twice as high as in the two other groups. In the slow-release caffeine group and the melatonin group, mean saliva cortis ol concentrations were significantly lower than control from day 2 to day 5 , whereas the placebo group had a mean saliva cortisol concentration signif icantly lower than the control value from day 2 to day 9. In conclusion, th ese results indicate that administration of slow-release caffeine, as well as of melatonin, allows a faster resynchronization of hormone rhythms durin g the 4 days following an eastbound flight incurring the loss of 7 h.