Objective To investigate the factors associated with depression, including the serum oxytocin (OXT) levels, disease activity, activities of daily living (ADLs) and quality of life (QOL), and their effects on rheumatoid arthritis (RA).

Methods This study included 42-RA-patients. We measured the following variables before and after 6 months of treatment with biological disease-modifying antirheumatic drugs (bDMARDs): the baseline characteristics (including age, sex, disease duration, smoking, and body mass index), the doses of prednisolone and methotrexate, the serum level of matrix metalloprotease-3, the erythrocyte sedimentation rate and the C-reactive protein level. The disease activity of RA was assessed using the Simplified Disease Activity Index (SDAI), depression was assessed using the Hamilton Depression Rating Scale (HAM-D), the ADLs were assessed using the Health Assessment Questionnaire disability index and the QOL was assessed using the Short Form (SF)-36. The serum OXT levels were determined using an enzyme-linked immunosorbent assay.

Results The HAM-D score was significantly correlated with the SDAI, and the mental component summary score of the SF-36. However, the serum OXT levels were not correlated with the HAM-D score. The serum OXT levels before and after bDMARDs treatment did not differ to a statistically significant extent, regardless of the presence of depression. Although the differences in the serum levels of OXT were observed prior to the initiation of treatment, there was no gender difference after treatment.

Conclusion Although RA complicated by depression may be related to the following high disease activity, a poor QOL and poor ADLs, the serum OXT levels were not directly correlated.