Amplitude of the oral temperature circadian rhythm and the tolerance to shift-work.

The aim of the study was to test the hypothesis of a relationship between the tolerance to shift-work and the amplitude of the oral temperature circadian rhythm. Forty eight shift-workers (Rhône-Alpes Region) volunteered for this chronophysiological investigation: a) 23 steel-industry workers (SI); shift-duration: 7 days (weekly rotation); b) 25 chemical-industry workers (CI); shift-duration 2 days. The subjects' ages were roughly similar with regard to groups (SI and CI) as well as sub-groups (good and poor tolerance of shift-work). The tolerance was evaluated conventionally, according to both the existence and intensity of 3 types of medical complaint: (1) digestive troubles: gastritis, colitis, peptic ulcer etc.; (2) persisting fatigue, unusual nerviness, etc.; (3) sleep alterations. The poor tolerance was observed mostly in subjects shift-working for 10 years or more. Regular large-scaled and retested medical Hg thermometers (1/20 Celsius precision) were used. Data were recorded 2-hourly, at fixed clock hours in order to obtain individual time series. Both conventional and cosinor statistical analysis show that, in both groups, the oral temperature circadian amplitude is larger in subjects tolerant to shift-work than in subjects that have become intolerant.