The relationship between the systemic immune-inflammatory index (SII) and circadian syndrome (CircS) is unclear. This study aims to explore this association. We extracted 23,148 participants from the National Health and Nutrition Examination Surveys 2005 to 2018. We used 3 multivariate logistic regression models to investigate the associations between SII and CircS, along with restricted cubic splines and subgroup analyses. The participants with CircS tended to be older and female. They had higher body mass index, poorer liver function, lower levels of education, and economic status compared with non-CircS participants. The SII level in the CircS group was higher than in the non-CircS group (odds ratio = 1.25, 95% confidence interval = 1.09–1.44, P = .002). There was no significant nonlinear relationship between SII and CircS ( P overall .05). We demonstrated a positive association between SII and CircS, particularly among people with low body mass index, low physical activity, cardiovascular disease, or cancer. For these populations, we may identify and intervene in CircS at an earlier stage by monitoring SII.
Lu et al. (2026) studied this question.