Objective To examine if salivary cortisol is associated with depressive symptoms and clinical depression among public sector employees.
Method In 2007, 10,036 public sector employees received a questionnaire along with salivary cortisol test tubes for home administration. A morning (30 min after awakening) and evening (2000 h) salivary sample were collected. 3,536 employees returned questionnaires and valid saliva samples. A subsample of participants (n = 387) collected three morning saliva samples (at awakening, 20min and 40min after awakening) plus an evening sample (2000 h). Participants were approached again in 2009 with questionnaire and salivary test tubes (n = 2,408). Participants with self-reported depressive symptoms (Common Mental Disorder Questionnaire) were invited to a SCAN interview (Schedules for Clinical Assessment in Neuropsychiatry, version 2.1) to determine clinical depression. The repeated cross-sectional data were analysed with logistic regression. Odds ratios of depressive symptoms and of clinical depression were estimated for morning, evening, mean and the difference between morning and evening cortisol (slope). For the subsample, CAR (awakening cortisol response) and AUC (the area under the curve) cortisol measures were calculated. We adjusted for gender, age, income, education, family history of depression, physical activity and alcohol consumption.
Results In 2007 the median level of cortisol was 12.5 nmol/l in the morning and 2.1 nmol/l in the evening. None of the measures of salivary cortisol were associated with self-reported depressive symptoms or clinical depression, neither in 2007 or 2009. E.g. in 2007, the odds ratios of depressive symptoms by a one unit increase in morning and evening cortisol (log[nmol/litre saliva]) were 0.97 (95% CI: 0.83–1.13) and 1.05 (0.92–1.20), respectively, and of clinical depression 1.08 (95% CI: 0.35–3.36) and 0.66 (0.30–1.45), respectively.
Conclusion Salivary cortisol was not associated to self-reported symptoms of depression or to clinical depression.