Apparent phase-shifts of circadian rhythms (masking effects) during rapid shift rotation

Abstract

Six subjects worked an experimental 8 h rapidly rotating shift system in which 6 shifts were compressed into 5 d (work two mornings - 8 h interval - work two nights - 8 h interval - work two afternoons). Rectal temperature was continuously recorded and urinary excretion rates of adrenaline, noradrenaline, K+, Na+ and Hg+ were assessed in samples collected at 4 h intervals. Higher rectal temperatures and higher excretion rates of the two each catecholamines than those expected from the normal circadian rhythms were observed during night work, while lower than expected values were recorded forenoon sleep. In these three rhythms, immediate, significant 3-4 h delay phase-shifts occurred in the two days following night shifts. The acrophases reverted suddenly to their initial positions when the subjects returned to their normal sleep/wake schedule. The circadian rhythms of the excretion of electrolytes were not perceptibly disturbed. It is concluded that the apparent phase-shifts were due to a direct influence (masking effect) of the changes in body functions during sleep and wakefulness on the measured parameters, and that no true phase-shifts (entrainment) occurred in the endogenous circadian regulation. The evidence of such an immediate, partial adaptation to unconventional sleep/wake patterns supports the adoption of rapidly rotating shift systems which would not greatly interfere with the endogenous oscillators.

Intra-individual variability in sleep duration and fragmentation: Associations with stress

“…However, given the substantial nightly variability in such parameters, this component may also be important to consider. Importance of variability in sleep for health is consistent with findings showing increased rates of disease among individuals employed in rotating shift work, and adjustments in shift work schedules altering physiological responses such as catecholamine excretion (Vokac et al, 1981; Orth-Gomer, 1983). Understanding the determinants of variability in sleep that is not imposed by shift work may have implications for both sleep and health research.…”

The Circadian Clock and Human Health

“…Social schedules (e.g., work and school times) predominantly act on the circadian/sleep network via behaviour (arrow S) and can lead to discrepancies between social and biological timing (SJL) [33]. These discrepancies may include being awake, sleeping and eating outside the times specified by optimal entrainment without substantially changing the clock's phase (similar to masking [82]). People working standard rotational shifts, for example, frequently revert to their usual free-day sleep times when they need not work [83], suggesting that the phase of the clock (as represented by the SCN) remains relatively stable (depending on roster and light exposure during the night shift).…”

Keep Your Mask On: The Benefits of Masking for Behavior and the Contributions of Aging and Disease on Dysfunctional Masking Pathways

“…This comes at a great cost to the shift workers, especially if they flip-flop from being night-active when working to becoming day-active on their days off ( Åkerstedt and Wright, 2009 ). When this is done, the circadian system is unable to fully adjust to the shift work, and therefore humans are only able to stay awake at night because the masking system is overriding the endogenous circadian rhythm that is misaligned with behavior ( Vokac et al, 1981 ). Nurses that engage in many years of shift work have been shown to be at a higher risk of developing breast cancer ( Szkiela et al, 2020 ), depression ( Booker et al, 2020 ; Park et al, 2020 ), and anxiety ( Booker et al, 2020 ).…”