Objectives: Sleep quality and duration are significantly associated with metabolic syndrome (MetS), especially among individuals in the middle-aged and elderly age groups; however, it is inconsistent among the age groups in previous studies. This study investigated the effect of age on the association between sleep and MetS in a large sample size.Methods: Health-related data on MetS in males and females (n=22,995; age: 23?79 years) were collected from annual health examinations, including the Pittsburgh Sleep Quality Index (PSQI). MetS was diagnosed based on the 2009 Joint Interim Statement.Results: In total, 4,660 (20.3%) participants were diagnosed with MetS. The data showed a significant association between poor sleep quality (PSQI >5), shorter sleep durations (<6 hours), and MetS in the older group (≥40 years) after adjusting for age, smoking status, alcohol consumption, sex, and exercise. However, this association was not observed in the younger group (<40 years). Regardless of age, global PSQI scores and sleep durations were significantly related to abdominal obesity (male ≥90 cm, female ≥85 cm in waist circumference) and general obesity (body mass index ≥30 kg/m²).Conclusions: This study demonstrates that sleep quality and duration are relat...