White blood cell count as a mediator of the relationship between depressive symptoms and all-cause mortality: A community-based cohort study

Abstract

Background and objectivesOne possible pathway by which depressive symptoms influence all-cause mortality is through their relationship with markers of inflammatory response. We aimed to examine whether white blood cell (WBC) count mediated the relationship between the presence of depressive symptoms and all-cause mortality among older Chinese people. MethodsThis community-based cohort study targeted 4053 individuals aged 60 years or over. A bootstrapping approach was applied to examine whether WBC count mediated the relationship between the presence of depressive symptoms and all-cause mortality. WBC count was evaluated as a mediator. The presence of depressive symptoms was assessed by the nine-item Patient Health Questionnaire (PHQ-9). The mediating effect was considered significant if the 95% confidence interval (CI) did not include 0. ResultsMediation analysis indicated that WBC count played an important mediating role in the relationship between PHQ-9 score and all-cause mortality based on the significance of indirect effect (β = -0.0039, 95% CI = -0.01, -0.0009). The direct effect from PHQ-9 score to all-cause mortality was not statistically significant (P = 0.11) after adjusting for WBC count. ConclusionWBC count was associated with depressive symptoms and all-cause mortality. The association of depressive symptoms with all-cause mortality was fully mediated by WBC count.