Bidirectional association between psoriasis and depression: Two longitudinal follow-up studies using a national sample cohort

Background: Few studies have investigated the bidirectional association between psoriasis and depression. The aim of our study was to identify the association between psoriasis and depression. Methods: Data collected by the Korean Health Insurance Review and Assessment from 2002 to 2013 were used. In study I, psoriasis patients (n = 10,932) were matched 1:4 with control I group participants. In study II, depression patients (n = 60,383) were matched 1:4 with control II group participants. Matching was performed for age, sex, income, and region of residence. The stratified Cox-proportional hazard model was used to calculate the hazard ratio (HR) with crude and adjusted models. Results: In study I, the adjusted HR for depression was 1.13 (95% confidence interval (CI) = 1.03-1.24) in the psoriasis group compared to the control I group. In study II, the adjusted HR for depression was 1.11 (95% CI = 1.00-1.22) in the depression group compared to the control II group. In the subgroup analyses, the adjusted HRs for depression were 1.24 (95% CI = 1.00 - 1.53) in females aged < 40 years and 1.31 (95% CI = 1.04 1.66) in males aged >= 60 years. In the subgroup analyses from study II, the adjusted HRs for psoriasis were 1.56 (95% CI = 1.15 - 2.12) in males aged < 40 years and 1.35 (95% CI = 1.04 - 1.75) in males aged >= 60 years. Conclusions: We suggest that psoriasis and depression might have a bidirectional association.