Night and Shift Work and Transmeridian and Space Flights

Shift workers, including night workers in industry, hospitals, communication systems, surface transportation (railroad, bus and truck drivers), air transportation (pilots, flight attendants and passengers of transmeridian flights) are exposed to shift(s) of those environmental factors which synchronize human biologic rhythms. In this chapter we shall refer exclusively to a phase shift (ΔΦ) of synchronizers (or zeit- gebers) equal to or larger than 5 h, whether they result from a transmeridian flight across five time zones (e. g., Paris to New York) or a shift from a daytime to a night time work schedule. This qualification is related to two important facts: (a) synchronizing effects of environmental clue and cue are identical whether or not the geographical location has changed (Halberg and Reinberg 1967; Reinberg and Smolensky 1983). In other words, chronobiologic problems are similar for both the air hostess with a transmeridian flight and the nurse shifting from a day to night schedule, (b) A single ΔΦ≤ 5 h of synchronizers has either minor or more frequently no detectable chronobiologic effects (Halberg and Reinberg 1967; Klein and Wegmann 1979; Gundel and Wegmann 1989). A 1-h ΔΦ resulting, for example, transition to or from daylight saving time has no objectively demonstrable effect on either adults or schoolchildren (Reinberg et al. 1989a). Each organism exposed to a ΔΦ ≥ 5 h of environmental factors has to resynchronize its biologic time structure, which in practical terms implies that all its biologic clocks have to be reset to the “new” local time or adjusted to the “new” timing of work hours. We call this process “circadian adjustment of rhythms.”