Clinical and non-clinical depressive symptoms and risk of long-term sickness absence among female employees in the Danish eldercare sector

Background: Depression has a high point and life time prevalence and is a major cause of reduced work ability and long-term sickness absence (LTSA). Less is known of the extent to which non-clinical depressive symptoms are related to the risk of LTSA. The aim of this study was to investigate how non-clinical and clinical depressive symptoms are prospectively associated to subsequent LTSA.

Methods: In a cohort study of 6985 female employees from the Danish eldercare sector depressive symptoms were measured by the Major Depression Inventory (MDI) and scores (0-50) were divided into groups of 0-4, 5-9, 10-14, 15-19, ≥20 points and clinical depression. Data was linked to a national register with information on LTSA (≥3 weeks). Hazard ratios (HR) for LTSA during a 1-year follow-up were calculated by Cox's proportional hazards model.

Results: Compared to the reference group (0-4) the HR was stronger for each subsequent group: MDI scores of 5-9: HR=1.07 (95% CI: 0.93-1.24); 10-14: 1.38 (1.15-1.66); 15-19: 1.54 (1.20-1.98); ≥20: 1.96 (1.45-2.64); clinical depression: 2.32 (1.59-3.38); after adjustment for previous LTSA, age, family status, smoking, leisure time physical activity, BMI, and occupational group.

Limitations: Missing information on the cause of sickness absence and prevalent somatic illness.

Conclusion: A clear dose-response relationship exists between increasing depressive symptoms and risk of LTSA. The adverse effect of non-clinical depressive symptoms on LTSA already manifests itself at relatively low scores.

Clinical relevance: this study illustrates the valuable information of considering the whole continuum of depressive symptoms.