Abstract
Non-optimal sleep duration is associated with systemic inflammation and adverse health outcomes, whereas oral functional impairment has been linked to systemic diseases. However, the mechanisms linking sleep and oral function remain unclear. This study examined the association between sleep duration and perceived masticatory difficulties and whether leukocyte-derived inflammatory markers mediated it. This cross-sectional study included 8,252 adults (mean age, 51.1 years; 59.7% men) undergoing routine health checkups between April 2024 and March 2025. Sleep duration was categorized as < 5, 5-6, 6-7, 7-8, and ≥ 8 h. Perceived masticatory difficulties were assessed using a standardized questionnaire. Systemic inflammation was evaluated using white blood cell (WBC) and differential leukocyte counts. Multivariable regression, restricted cubic spline, and mediation analyses were performed. Masticatory difficulties were reported by 733 participants (8.9%). Those sleeping 7-8 h had the lowest odds of masticatory difficulties. Restricted cubic spline analysis demonstrated a significant non-linear association between sleep duration and monocyte levels (P for non-linearity = 0.03), with higher levels at shorter sleep durations and a modest increase at longer durations. Mediation analysis showed a significant indirect effect through monocyte count (indirect effect = - 0.0031; 95% confidence interval, - 0.0072 to - 0.0003), whereas WBC, neutrophil, and lymphocyte counts showed no significant indirect effects. Non-optimal sleep duration was associated with perceived oral functional impairment, partly mediated by monocyte-related inflammation. These findings suggest a potential inflammatory pathway linking sleep and oral function, with monocyte count identified as the sole significant mediator, and support medical-dental collaboration in preventing systemic diseases.