The circadian melatonin and cortisol secretion pattern in permanent night shift workers

Abstract

In permanent night shift workers the impact of environmental time cues on the circadian system is conflicting. Rhythm adjustments to the nocturnal work schedule have been described, and their significance for tolerance to shift work is under discussion. Reports concerning the effect of this work situation on the setting of the endogenous clock are, however, inconsistent. We examined nine healthy young male permanent shift workers with high work satisfaction at the end of a week on night work and seven male controls with normal diurnal working hours. All subjects were admitted to a research facility for 28 h, and blood was collected with a continuous-withdrawal pump in portions taken hourly for the estimation of the circadian melatonin (MT) and cortisol secretion pattern. One control did not exhibit a circadian secretion pattern. When compared with the other controls (n = 6), all except one of the shift workers showed no difference in the phase or phase relationship of their hormonal profiles. In the shift workers, a minor trend toward elevation of the MT amplitude and an increase in two indicators for the amount of MT secreted were noticed. One individual displayed inverse hormone rhythms with an undisturbed phase relationship of MT and cortisol and inconspicuous hormone amplitudes. He showed, however, an inverse day-night rhythm in his private life, too. The data collected suggest that even permanent night workers with a high degree of work satisfaction do not usually lose the diurnal orientation of their endogenous clock. Factors other than reorientation of the circadian system may be more important for high tolerance to shift work.

A Laboratory Comparison of Clockwise and Counter-Clockwise Rapidly Rotating Shift Schedules, Part III: Effects on Core Body Temperature and Neuroendocrine Measures

“…The findings of Roden et al (1993) are opposed to others who found wide variations in melatonin profiles, particularly the onset of melatonin release, among permanent night shiftworkers when compared to day workers (Weibel, Spiegel, Gronfier, Follenius, & Branden-Berger, 1997). Others have found forward shifts in the mean peak of melatonin as well as a lack of an identifiable acrophase during night work among permanent night shiftworkers (Quera-Salva, Defiance, Claustrat, DeLattre, & Guilleminault, 1996).…”

“…Produced by the pineal gland following its synthesis from tryptophan, concentrations of melatonin are relatively high at night and at their lowest levels during the day with the rhythm entrained by photic stimuli, exercise, certain drugs, and exogenous melatonin (Guyton & Hall, 2000). Roden, Koller, Pirich, Vierhapper, and Waldhauser (1993) examined the circadian melatonin profile for permanent night shiftworkers, compared with matched controls. The night shiftworkers as a group displayed no adaptation of circadian profiles for either melatonin or cortisol.…”

Mortality of Shift Workers

“…One issue would be to find a better variable measuring the circadian phase. Shift work is not a valid proxy since previous studies have shown that shift workers do not always have a phase shift of the circadian rhythm (8,9). Another problem to investigate would be whether the body is more sensitive or vulnerable as a result of shift work at certain ages.…”

Adverse metabolic and cardiovascular consequences of circadian misalignment

“…The endogenous circadian timing system, including the suprachiasmatic nucleus (SCN) in the hypothalamus and peripheral oscillators in vital organs, optimally regulates much of our physiology and behavior across the 24-h day when it is properly aligned with the sleep/wake cycle. However, shift work is generally associated with chronic misalignment between the endogenous circadian timing system and the behavioral cycles, including sleep/wake and fasting/ feeding cycles (7,8). Shift workers often experience symptoms akin to jet lag, with gastrointestinal complaints, fatigue, and sleepiness during the scheduled wake periods, and poor sleep during the daytime sleep attempts (9).…”