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Katarzyna Burek, Sylvia Rabstein, Thomas Kantermann, Céline Vetter, Markus Rotter, Rui Wang‑Sattler, Martin Lehnert, Dirk Pallapies, Karl-Heinz Jöckel, Thomas Brüning, Thomas Behrens

• To examine the effect of night shift on salivary cortisol at awakening (C1), 30 min later (C2), and on the cortisol awakening response (CAR, the difference between C2 and C1). We compared shift and non-shift workers with a focus on the impact of worker chronotype. Our study included 66 shift-working females (mean age = 37.3 years, SD = 10.2) and 21 non-shift working females (mean age = 47.0 years, SD = 8.9). The shift workers collected their saliva samples at C1 and C2 on each two consecutive day shifts and night shifts. Non-shift workers collected their samples on two consecutive day shifts. We applied linear mixed-effects models (LMM) to determine the effect of night shift on CAR and log-transformed C1 and C2 levels. LMMs were stratified by chronotype group. Compared to non-shift workers, shift workers before day shifts (i.e. after night sleep) showed lower cortisol at C1 (exp (\(\hat \beta\))=0.58, 95% CI 0.42, 0.81) but not at C2. In shift workers, the CARs after night shifts (i.e. after day sleep) were lower compared to CARs before day shifts (\(\hat \beta\)= − 11.07, 95% CI − 15.64, − 6.50). This effect was most pronounced in early chronotypes (early: \(\hat \beta\)= − 16.61, 95% CI − 27.87, − 5.35; intermediate: \(\hat \beta\)= − 11.82, 95% CI − 18.35, − 5.29; late: \(\hat \beta\)= − 6.27, 95% CI − 14.28, 1.74). Chronotype did not modify the association between night shift and CAR. In our population of shift workers, there was a mismatch between time of waking up and their natural cortisol peak at waking up (CAR) both during day and night shift duties.