The effect of triglycerides in the associations between physical activity, sedentary behavior and depression: An interaction and mediation analysis

Previous studies reported that there were associations between physical activity (PA), sedentary behavior (SB), triglycerides (TG) and depression. However, it is unclear whether there is an interaction and/or mediation effect of TG in the associations between PA, SB and depression. This study was to explore the effects of TG in the associations between PA, SB and depression, respectively.Our study included 7,728 adults (aged ≥20 years) participating in the 2009-2018 National Health and Nutrition Examination Survey (NHANES), which was a nationally representative survey. With higher TG as a mediator, a four-way decomposition method was used to decompose the total effects of insufficient PA and prolonged SB on depression, respectively.There were statistically significant associations between moderate-to-vigorous recreational activity (MVRA), SB, TG and depression (all P < 0.05), respectively. With higher TG as a mediator, there were interaction and mediation effects in the association between SB and depression, and the excess relative risk (95% CI) of reference interaction effect (INTref) and the total mediation effect were 0.15(0.01,0.29) and 0.03(0.00,0.06), respectively. While insufficient MVRA attributed a proportion of 80.42% for the controlled direct effect (CDE) and 6.28% for total mediation effect. In addition, similar findings were observed in those with hypertension, overweight/obesity, dyslipidemia, and metabolic syndromes.This was a cross-sectional study, and the ability to make causal inference was limited.The controlled direct effect of MVRA, the mediation of TG, and the interaction between SB and TG played the vital roles in increasing the risk of depression.