Objectives Common mental disorders are associated with impaired functioning and sickness absence. We examine whether sub-clinical as well as clinical psychiatric morbidity predict long spells of sickness absence for both psychiatric and non-psychiatric illness. We also examine whether recent common mental disorders and those present on two occasions have a stronger association with sickness absence than less recent and single episodes of disorder.

Methods Common mental disorders measured by the General Health Questionnaire were linked with long spells of sickness absence in 5104 civil servants from the longitudinal Whitehall II Study. Negative binomial models were used to estimate rate ratios for long spells of sickness absence with and without a psychiatric diagnosis (mean follow-up 5.3 years).

Results Clinical but not sub-threshold common mental disorders were associated with increased risk of long spells of psychiatric sickness absence for men, but not for women, after adjusting for covariates (rate ratios (RR) 1.67, 95% CI 1.13 to 2.46). Risk of psychiatric sickness absence was associated with recent common mental disorders (RR 2.08, 95% CI 1.29 to 3.35) and disorder present on two occasions (RR 1.65, 95% CI 0.98 to 2.71) for men only. Common mental disorders were not associated with increased risk of non-psychiatric sickness absence after adjustment for covariates.

Conclusions Identification and treatment of common mental disorders may reduce the economic burden of long term psychiatric sickness absence. Our results suggest that public health and clinical services should focus on the identification of workers with elevated mental health symptoms. Studies are needed of the efficacy of early identification and management of mental health symptoms for the prevention of long spells of sickness absence.