To explore the association between the systemic immune-inflammation index (SII) and adult obesity, and to provide insights for the prevention and early diagnosis of obesity.

This study was based on the survey data of the National Health and Nutrition Examination Survey (NHANES). A binary logistic regression model was used to evaluate the relationship between the systemic immune-inflammation index and obesity (general obesity, central obesity) by calculating the odds ratio (OR) and its 95% confidence interval (CI). In addition, stratified analysis was performed by age (< 60 years old and ≥ 60 years old) and gender.

After adjusting all covariates, when general obesity was taken as the outcome variable, compared with the subjects in the lowest quartile (Q1) of SII, the risk of general obesity in the subjects in the third quartile (Q3) increased by 0.374 times (OR=1.374, 95%CI: 1.111-1.699); the risk of general obesity in the subjects in the fourth quartile (Q4) increased by 0.843 times (OR=1.843, 95%CI: 1.490-2.281). When central obesity was taken as the outcome variable, compared with the subjects in Q1, the risk of central obesity in the subjects in Q3 increased by 0.542 times (OR=1.542, 95%CI: 1.189-2.000); the risk of central obesity in the subjects in Q4 increased by 1.036 times (OR=2.036, 95%CI: 1.553-2.670). In addition, the results of stratified analysis showed that the relationship between SII and obesity was different among different ages and was only significant in the population aged <60 years old.

SII is positively correlated with the risk of adult obesity, and the higher the SII, the higher the risk of obesity. In addition, the relationship between SII and obesity may be age-specific.