Effects of mental disorders on the relationship between physical activity and bone markers among depressed patients in Germany.

Objective: Physical activity (PHYA) positively influences bone health, but this relationship might be affected by mental disorders. Aims: (1) evaluate whether mental disorders influence bone markers and (2) whether the relationship of PHYA with bone markers is influenced by mental disorders. Methods: A secondary data analysis of the longitudinal DEPREHA-study (Germany, 18 months, n = 208, 18-65y, ICD-10 F32.x-F33.x, collected 2015-2017) was conducted. Baseline data: sociodemographic, PHYA, depressive (BDI-II) and psychosomatic (SCL-90) symptoms; bone markers procollagen-type-1-N-propeptide (P1NP), osteocalcin (OC) and crosslaps (CTx) were analyzed. Multiple linear regressions assessed associations of depressive and psychosomatic symptoms with bone markers and moderating effects of depressive and psychosomatic symptoms on the PHYA-bone marker relationship; Mediation analyses were conducted with the PROCESS macro. All analyses were conducted in IBM SPSS (v31.0; p < 0.05). Results: Data from n = 44 depressed participants were eligible for analysis. Significant associations of BDI-II and SCL-90 with P1NP and OC were detected. A significant moderation of SCL-90 on the relationship of PHYA with P1NP (p < 0.05), but no mediation effect of BDI-II or SCL90 on bone markers was detected. Conclusions: Depressive and psychosomatic symptoms influence and may potentially moderate the relationship between PHYA and bone markers, which should be considered in further studies and therapeutic planning.