Bickhardt‘s correspondence raises important questions. From a chronobiological perspective and based on observations and experimental studies, the old guideline of the German society for occupational and environmental medicine (Deutsche Gesellschaft für Arbeitsmedizin und Umweltmedizin, DGAUM) recommended planning no more than three sequential night shifts in forward rotation. The main argument for this was that because of the 24 hour rhythm of the circadian time cues (zeitgeber) daylight and social life, chronobiological adaptation—as seen when travelling through time zones—is not possible in the context of shift work. This means that the stress burden increases continually, night after night. As several short breaks are more effective than fewer, longer ones, the stress periods should be kept as brief as possible. Observational studies from the real working environment that is the hospital (1) and a meta-analysis of intervention studies (2) have confirmed the validity of this concept. Introducing short shift sequences had a positive effect on health indicators such as sleep or melatonin concentrations. However, in an environment of multifactorial events, unfavorable physiological effects owing to long shift sequences or permanent night work may be counterbalanced by more favorable psychosocial stressors—for example, as a result of better compatibility of professional and personal challenges.
A new consensus based (S2k) guideline on night work and shift work has been announced and will probably be published in 2018. The systematic reviews undertaken to set out the guideline already indicate that the existing data cannot provide an answer to the question of which shift working system poses the smallest risk for long term health sequelae, such as depression, myocardial infarction, or metabolic syndrome.
The age after which the chronobiological adaptability is reduced to the extent that shift work becomes an impossibility also remains an unanswered question. It is a known fact that the tolerance for shift work decreases with the aging process (3). People‘s adaptability, however, develops in very different ways, so that no convincing arguments can be brought forward in favor of fixed age thresholds.
Footnotes
Conflict of interest statement
The authors of both letters to the editor declare that no conflict of interest exists.
References
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