Depression and somatic disorders are closely interrelated. Depressed mood is recognized to contribute to the development and progression of wide range of somatic diseases, while at the same time somatic diseases may increase the risk of depression. Co-morbidity research still represents huge research and clinical challenge to contemporary psychiatry and medicine.

To check whether the correlation of NSC and poor prognosis of MDD treatment is merely the consequence of age and duration of illness.

We investigated a cross-sectional sample consisting of 290 psychiatric diagnosed with MDD. Outcome was the number of psychiatric rehospitalizations (NPR) since the first diagnosis of MDD treatment success. Predictor was NSC. Covariates controlled were sex, age, BMI, marital status, number of household members, education, work status, duration of MDD, CGI-severity of MDD at diagnosis, treatment with antidepressants and anti-psychotics.

After adjustment for all confounders, mediation analysis revealed insignificant indirect effects of NSC on NPR through patient's age (P = 0.296) and duration of MDD (P = 0.180). Direct effect of NSC was significant and clinically relevant (P < 0.001). Effect of NSC was significantly moderated by duration of MDD (P = 0.019). NSC and NPR were not significantly associated if MDD lasted for less than a year. The more MDD lasted the stronger was correlation of NSC and NPR.

Correlation of NSC and poor prognosis of MDD is not a mere consequence of patient's age and duration of illness. To treat MDD effectively we have to treat simultaneously somatic comorbidities.

The authors have not supplied their declaration of competing interest.