Circadian Rhythm Amplitude and Individual Ability to Adjust to Shift Work

Abstract

The magnitude of the circadian acrophase adjustment (Δφ) following a phase shift of socio-ecologtc synchronisers (Δψ) such as results from shift work varies from subject to subject. According to Aschoff (1976) the ability to adjust φ rapidly could be negatively related to the amplitude of certain circadian rhythms. To test this hypothesis the correlation coefficient (r) between the mean rhythm amplitude A and the acrophase shift Δφ after the first night shift was calculated for several variables from estimates of chronobiological time series analyses (single cosinor) in two groups of selected shift workers. Statistically significant negative correlations (ranging from −0.53 to −0.63) between A and Δφ were observed in the circadian rhythms of oral temperature, peak expiratory flow and urinary 17-OHCS, but not for grip strength, urinary K ⁺ and Na ⁺ A low amplitude of certain circadian rhythms could thus be considered as a measure of individual ability to adjust to shift work easily. It is posssible that other chronobiological characteristics may be found which will increase the value of this type of measure.