Abstract: Background: Traditional indicators like BMI are insufficient for comprehensive assessment of children's nutritional status and health risks. Body composition analysis offers a more precise method to evaluate the distribution of fat, muscle, and water content in children's bodies, providing new avenues for health assessment. Objective: To investigate the correlation between body composition and blood pressure levels among schoolage children in two southwestern provinces and one municipality (Sichuan, Guizhou, Chongqing) of China, providing scientific evidence for early prevention of childhood hypertension. Design: Crosssectional survey. MethodsUsing multistage stratified cluster sampling, students from primary and secondary schools in the three areas were recruited. Data on basic information, family circumstances, pubertal development, family medical history, nutritional status, and dietary habits were collected through questionnaires. Standardized physical measurements, blood pressure measurements, and body composition parameters (body fat percentage, muscle ratio, water content, protein, and mineral content) were obtained using bioelectrical impedance analysis. Univariate analysis was conducted for included variables, and restricted cubic splines (RCS) analysis was used to explore the doseresponse relationship between body composition and elevated blood pressure risk. Main outcome measures: Association between body composition and blood pressure. Results: The study analyzed 8,397 students from six schools across the three areas, including 5,722 primary school students and 2,675 secondary school students; 4,593 from urban areas and 3,804 from rural areas. The mean age was (10.9±2.4) years, with 4,445 boys (52.9%) and 3,952 girls. Elevated blood pressure was detected in 784 students (9.3%), with higher prevalence in boys compared to girls, overweight/obese children compared to nonoverweight/obese children, those who had entered puberty compared to those who had not, and those with high salt intake compared to those without (all P<0.05). All five body composition indicators showed significant correlations with blood pressure (all P<0.05). Genderspecific patterns emerged in the relationship between body composition indicators and elevated blood pressure risk. In girls, body fat percentage, water content, muscle ratio, and protein content showed linear correlations with elevated blood pressure risk, while mineral content showed a nonlinear correlation. In boys, body fat percentage and mineral content showed nearly linear correlations with elevated blood pressure, while muscle ratio, water content, and protein content showed nonlinear correlations. Using medium levels of each gender as reference, only low body fat percentage and high water and protein content in boys showed no statistically significant differences in systolic blood pressure, diastolic blood pressure, and mean arterial pressure, while other parameters showed significant increases or decreases. Conclusion: Body composition is closely associated with elevated blood pressure in both male and female primary and secondary school students. Incorporating body composition analysis into cardiovascular health risk assessment may aid in early identification of elevated blood pressure in children.

Key words: School-age children, Body composition, Blood pressure