Comparison of a westward flight and an eastward flight in the circadian rhythms of plasma melatonin

We estimated the re-entrainment of plasma melatonin rhythm after an eastward flight to New York in 2000 and after a westward flight to London in 2001. Blood samples were taken at 1.5 h intervals for 24-h from eight subjects once before the flight and twice after the flight. They were exposed to natural zeitgeber outdoors. The symptoms of six subjects were moderate in London. All subjects showed the orthodromic re-entrainment, and the phase shift was small (46.3 min/day) in the westward flight. It seemed that the direction of flight was as important for jet lag symptoms as was sunlight exposure.