Circadian syndrome comprises metabolic risk factors and comorbidities associated with circadian rhythm disruption. However, whether overall diet quality is associated with circadian syndrome remains unclear. This study aimed to investigate the association between the Healthy Eating Index-2015 (HEI-2015), an indicator of overall diet quality, and circadian syndrome to address this knowledge gap. This cross-sectional study used data from the National Health and Nutrition Examination Survey conducted from 2005 to 2018, including adults aged 20 years and older. The HEI-2015 was used to assess individual dietary quality, while circadian syndrome was defined based on the components of metabolic syndrome, along with sleep deprivation and depression. In weighted multivariable logistic regression, HEI-2015 was modeled both as a continuous variable and in tertiles, with HEI-2015 as the independent variable and circadian syndrome (yes/no) as the dependent variable. Restricted cubic spline (RCS) analysis was used to examine potential dose-response relationships, and subgroup analyses were performed by age, sex, physical activity, body mass index, trouble sleeping, cardiovascular disease, chronic kidney disease, and cancer. A total of 11,557 participants (mean age 48.7 years; 51.4% female) were included in the study, of whom 3317 were defined as having circadian syndrome. The proportions of participants in HEI-2015 tertiles 1, 2, and 3 were 33.3%, 33.3%, and 33.4%, respectively. In the fully adjusted model, HEI-2015 was inversely associated with circadian syndrome when treated as a continuous variable (OR: 0.90, 95% confidence interval (CI): 0.86-0.94), and when categorized into tertiles, the odds ratio (OR) for the highest tertile compared with the lowest was 0.78 (95% CI: 0.67-0.90). RCS analysis indicated a linear negative association (P for nonlinearity = .11). The results of subgroup analyses were consistent across various subgroups. Among U.S. adults, higher HEI-2015 scores were linearly associated with lower risk of circadian syndrome. Further validation in more diverse populations is needed, and clinicians may consider assessing dietary quality in patients with circadian syndrome to optimize management strategies.
