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Mental health and physical health are intrinsically linked, yet the mechanisms are not well understood. We investigated whether moderate-vigorous physical activity (MVPA) mediated the association between depression and physical function (PF) in midlife. Individuals from two UK birth cohorts born within one week in 1958 (n = 7278) and 1970 (n = 6097) with data on depression (ages 33/34; Malaise Inventory), MVPA (age 42; self-reported) and PF (ages 50/56; Short Form-36 subscale). Covariates included sex, childhood and adulthood social class, maternal mental health, childhood mood, alcohol consumption, smoking habits, sleep, marital status, BMI and long-standing illness/disability. Linear or multinomial logistic regression models examined associations between depression, MVPA and PF. We used a parametric g-computation mediation analysis approach to estimate percent differences in PF. Depression was associated with less frequent MVPA and poorer PF. Lower MVPA was associated with worse PF. The direct effect – randomised analogue not operating via MVPA – of depression on PF was −18.8 % (95%CI:--25.8,-11.8) and −15.8 % (20.6,-11.0) in the 1958 and 1970 cohorts, respectively. The indirect effect – operating via MVPA – was −0.5 % (−1.0,-0.03) and −0.2 % (−0.6, 0.3), resulting in a total proportion mediated of 3.1 % (0.1, 6.0) and 0.9 % (−1.6, 3.4). MVPA was self-reported. Intermediate confounders and mediators were measured at the same age, however associations did not change in sensitivity analysis considering age 46 MVPA (1958 cohort). Although higher MVPA was protective against poor PF, there was only minor evidence that it mediated the association between depression and PF. Further investigation into other potential mediators of pathways from mental to physical health is needed. • We studied MVPA as a mediator between depression and physical function. • Depression was associated with less frequent MVPA and worse physical function. • More frequent MVPA was associated with better physical function. • However, MVPA only mediated 0.9 to 3.1 % of the association. • Further inquiry of other mediators (e.g. sedentary behavior, sleep) is needed. [ABSTRACT FROM AUTHOR]

Background: Adolescent depression can severely interfere with age-appropriate and lifetime development and functionality. Physical functioning in daily life (as a means of individual support) as well as social support from family and friends have been shown to enhance adolescent resilience against depression. By applying a multisystemic model of resilience, this study investigates how these resources reciprocally influence each other and how they interact with depression over time.Methods: Longitudinal data (three assessments over three years) from the Resilient Youth in Stressed Environments project was analyzed using panel network analysis to investigate short- and long-term uni- and bidirectional effects. The sample consisted of N = 500 adolescents from Canada (mean age = 18.49, SD = 3.01, 56.40% young women) at the first assessment.Results: Depression seemed to fluctuate, while the resources showed significant stability over the course of the study. Perceived family and friend support were not significantly influenced by depression while they had significantly negative temporal effects on depression. Only physical functioning showed a negative feedback loop, notably with somatic symptoms of depression. Family and friend support shared a reinforcing feedback loop, while physical functioning was not related to either type of support.Limitations: Future studies should address the low average of depressive symptomatology and subjective, global measures of social support.Conclusions: The resources show potential time-dependent effects: symptom-specific resources need to be applied in the short-term, while a pool of multisystemic resilience resources seems necessary over the long-term to increase the resilience to depression among adolescents. [ABSTRACT FROM AUTHOR]