Objectives: To examine the relationships between exposure to workplace factors (night-work, extended working hours, psychosocial work stress) and cortisol secretion, and to test whether workplace factors interact, resulting in combined effects.
Methods: Multiple linear and logistic regression was used to test relationships between workplace factors and cortisol secretion in the 1958 British birth cohort at 45y. Salivary cortisol was measured twice on the same day to capture the post-waking decline, facilitating the analysis of different cortisol patterns: (i) Time 1 (T1, 45min post-waking) (ii) Time 2 (T2, 3hrs after T1) (iii) average 3h exposure from T1 to T2 cortisol (iv) T1 to T2 change. To identify altered diurnal cortisol patterns we calculated (i) flat T1-T2 change in cortisol (ii) top 5% T1 (iii) bottom 5% T1 (iv) T1 hypo- or hyper-secretion. Models were adjusted for socio-economic position at birth and in adulthood, qualifications, marital status, dependent children, and smoking status.
Results: 25% of men and 8% of women were exposed to >1 workplace factor (night-work, extended work-hours, job-strain). Night-work was associated with a 4.28% (95%CI=1.21, 7.45) increase in average 3h cortisol secretion independently of job strain or work hours. Night workers not exposed to job strain had elevated T1 cortisol (5.81%, 1.61, 10.19), although for T2 cortisol it was night-workers exposed to low job control who had elevated levels (11.72%, 4.40, 19.55). Men (but not women) working >48 hrs/week had lower average 3h cortisol secretion (4.55%, -8.43, -0.50). There were no main effects for psychosocial work stress. All associations for T2 and average 3h cortisol secretion weakened slightly after adjustment for confounding factors, but associations for T1 cortisol were unaffected by adjustment.
Conclusions: Our study suggests that night-work in particular is associated with elevated cortisol secretion and that cortisol dysregulation may exist in subgroups with specific combinations of stressors.
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