Nurses who work 12-hour shifts have higher stress hormone levels in the morning and at night than those who work 8-hour shifts, meaning longer shifts put more strain on their body’s internal clock.
Claim Context
Shift workers on 12-hour shifts exhibit higher morning and evening cortisol levels compared to those on 8-hour shifts, suggesting that longer work durations exacerbate circadian disruption and stress hormone dysregulation.
“Zhang et al. observed that 12 h shift workers exhibited elevated morning saliva cortisol levels before the day shift (median 0.54 vs. 0.31, p < 0.005) and increased evening saliva cortisol levels following the night shift (median 0.51 vs. 0.31, p < 0.005) in comparison to 8 h shift nurses.”
Evidence from Studies
No evidence studies found yet.
What Would Prove This
Per GRADE and EBM methodology, here is what ideal scientific evidence would look like to definitively prove or disprove this claim, ordered from strongest to weakest.
A meta-analysis could quantify whether 12-hour shifts consistently lead to higher cortisol levels than 8-hour shifts across multiple healthcare settings.
A systematic review and meta-analysis of 10+ studies comparing cortisol levels (saliva/blood) in 8h vs. 12h shift workers, measuring at least 3 time points (awakening, noon, evening), adjusting for age, sleep duration, and shift rotation pattern.
An RCT could determine whether assigning workers to 8h vs. 12h shifts directly alters cortisol rhythms over time.
A crossover RCT of 60 nurses randomized to 3 months of 8h shifts followed by 3 months of 12h shifts (or vice versa), with cortisol sampled at 0, 30, 60, 12, and 22h daily, measuring CAR slope and diurnal amplitude as primary outcomes.
A cohort study could show whether workers on 12h shifts develop chronic cortisol dysregulation over years, compared to those on 8h shifts.
A 5-year prospective cohort of 300 new hires assigned to either 8h or 12h shifts, with annual cortisol sampling and sleep assessments, tracking development of blunted CAR and elevated evening cortisol.
A cross-sectional study could confirm the prevalence of elevated cortisol in 12h vs. 8h shift workers at a single point in time.
A cross-sectional survey of 1,000 nurses across hospitals measuring cortisol at awakening and bedtime, stratified by shift length (8h vs. 12h), adjusting for age, sleep duration, and shift rotation.
A case series could document extreme cortisol dysregulation in individuals working 12h shifts for decades.
A case series of 10 nurses with >15 years of 12h shift work, showing persistently elevated evening cortisol (>8 ng/mL) and blunted CAR (<1.5 ng/mL increase), with documented sleep and cardiovascular outcomes.