The mediating effect of engagement in physical activity over a 24-hour period on chronic disease and depression: Using compositional mediation model.

Background: Popular mediation method only considers a single activity as a mediator instead of all 24-hour physical activity, such as a four-way decomposition method. We investigated the mediation of 24-hour movement continuum between chronic diseases (cardiovascular disease [CVD] and diabetes) and depression using a novel compositional mediation model.

Methods: 24-hour activity data measured by accelerometer were obtained from NHANES 2005-2006. Adjusted coefficient with 95% confidence interval (95% CI) for PHQ-9 total score and adjusted odds ratio (OR) with 95% CI for depression were computed from compositional mediation models.

Results: In total, 2,375 participants aged ≥ 20 were included in our analysis. Both diabetes and CVD were associated with increased sedentary behavior (SB) and sleep and reduced moderate-to-vigorous physical activity (MVPA) and light-intensity physical activity (LPA), leading to an increased likelihood of depression. Although not all component indirect effects were associated with PHQ-9 total score and depression, the total indirect effect was significantly associated with both PHQ-9 total score (coefficient (95% CI) for diabetes: 0.162 (0.081, 0.261); coefficient (95% CI) for CVD: 1.139 (1.061, 1.240)) and depression (OR (95% CI) for diabetes: 0.235 (0.126, 0.362); OR (95% CI) for CVD: 1.200 (1.088, 1.346)) using the compositional mediation model.

Conclusion: We developed a compositional mediation model for continuous and binary outcomes, which can handle entire compositional mediators as a unit. The mediation of 24-hour movement continuum mediated the association between diabetes, CVD, and depression. Our findings present potential interventions for reducing risk of depression among patients with CVD and diabetes.