Table 3

Domains for capture in epidemiological studies.

DomainVariableCircadian impact
Working timeWork hours/week
Night work (non-day shift work)At least 3 h of work between midnight and 05:00Required to estimate phase shift and sleep perturbation
DurationYears employed in non-day shift workDuration of non-day shift work
IntensityNo of non-day shifts per month/yearRecovery time off between work periods
Cumulative exposureDuration times intensity over the work historyDose (burden) of non-day shift work
Permanent night shift (not rotating)No of consecutive days of night work, followed by number of days offPermanent night work is less disruptive only if phase shift is maintained also on days off
Rotating typeContinuous (365 days/year) or discontinuous (interruption on weekend)Different rotating shift schedules have a different impact on phase shift and adjustment
Direction of rotationForward (morning→afternoon/evening→night) backward (afternoon/evening→morning→night)Forward rotating shift schedules are less disruptive than backward ones
Rate of rotationDaily change, 2–3–4 day change, weekly, fortnightly change, etcRate of rotating shift schedules (fewer nights in a row) may have different impact on circadian disruption
Morning shiftNo of consecutive days of early morning shift (before 06:00)The earlier the morning shift starts, the more disruptive it is
Start and end time of shiftsDefines displacement from solar day and duration of the working hoursMay be relevant for phase shift, sleep deficit, and fatigue
Rest periods after shiftNo of rest-days after night shiftsThe shorter the rest period between shifts, the shorter the sleep and recovery
JetlagNo of time zones crossed; eastward versus westwardGiven the low prevalence in the general population, this is probably only needed in cohort studies of frequent trans-meridian travellers (eg, air crews), whereas jetlag studies should also include questions on shift work, since these often go hand in hand
SleepSleep duration in relation to type of shift; naps; sleep quality; sleepiness; sleeping problems (circadian disruption); possibility to sleep on duty (night shifts)Sleep/wake cycle and timing of sleep are important in phase shift and resetting, but they may also act as independent risk factors
Light at nightDuring sleep period, during night shift, at leisure timeBoth timing and intensity are important on circadian phase shift
Characteristics of the individualDiurnal type (morning person, evening person, neither)It influences differently adjustment and tolerance to night and morning shifts