Body core temperature fluctuates during the day following a sinusoidal variation with a maximum acrophase in the late afternoon. This circadian rhythm is mainly endogenous but it can be influenced by environmental factors such as work and social and physical activities.

1) To verify if aluminum shift-workers would present different core temperatures at different times of the day (i.e. diurnal variations); 2) To characterize these diurnal variations and their consequences.

Twenty-nine employees from the aluminum industry participated in this preliminary study. They worked indoors where the temperature was typically in excess of 40°C. In addition, each worker wore protective clothing consisting of suit, gloves and mask. Core temperature (ingestible pill) data covering a 24-hour circadian cycle were obtained in 10 workers during morning, afternoon and night shifts. Circadian variation in temperature was characterized using a cosinus function (cosinor model). The mesor (average) and acrophase of the function have been calculated for each participant.

Core temperatures recorded on the work site were significantly higher in the afternoon or early evening (from 12:00h to 20:00h) than at night or during the early morning (from 21:00h to 08:00h). These differences were not triggered by the work duration but by the time of day. There were large differences between the individual accrophase times, probably due to different working activities as well as the influence of synchronization/shift from the previous days. However, core temperature was consistently higher in the afternoon than during the morning or night. The circadian variation in body core temperature showed a mesor of 37.45°C. This represents an average core temperature half a degree higher than generally observed in the general population at rest.

The current data showed that workers from the aluminum industry present a relatively elevated average core temperature, with the highest values being reached during the afternoon shift. This suggests that special attention should be given to the afternoon shift and that break/cooling procedures should be implemented if necessary. These preliminary observations have to be completed by clinical and behavioral observations.


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