[The cumulative effects of lifestyle on different patterns of multimorbidity among children and adolescents aged 9-18 in Tianjin City].

<b>Objective:</b> To understand the occurrence of different patterns of multimorbidity among children and adolescents aged 9-18 in Tianjin and analyze the cumulative effects of lifestyle on these patterns of multimorbidity. <b>Method:</b> From September to November 2022, a stratified cluster random sampling method was used to select students from primary schools, junior high schools, general high schools, and vocational schools in 16 districts of Tianjin to screen for height, weight, blood pressure, distant vision, and diopter. One year later, a follow-up measurement and questionnaire survey were conducted. The log-binomial model was used to analyze the strength of the association between lifestyle factors and different patterns of multimorbidity. <b>Results:</b> The age of 9 488 students was (12.37±2.49) years old, including 4 999 boys and 4 489 girls. The detection rates of three patterns of multimorbidity of overweight obesity and high blood pressure, overweight obesity and myopia, and overweight obesity with high blood pressure and myopia were 6.63%, 9.32%, and 4.21%, respectively. The detection rates of the three types of multimorbidity in boys were higher than those in girls (all <i>P</i><0.001). The detection rate of overweight obesity and high blood pressure in suburban areas was higher than that in urban areas (<i>P</i>=0.002). The detection rate of overweight obesity and myopia in suburban areas was lower than that in urban areas (<i>P=</i>0.034). The detection rate of overweight obesity and myopia among those aged 9-12 years old was higher than other age groups (all <i>P</i><0.001). The <i>ARR</i> (95%<i>CI</i>) for the association between favorable physical activity and the occurrence of overweight obesity and high blood pressure was 0.79 (0.68-0.92). The <i>ARR</i> (95%<i>CI</i>) for the association between favorable physical activity and the occurrence of overweight obesity with high blood pressure and myopia was 0.82 (0.67-0.99). Compared with children and adolescents with 0-2 favorable lifestyle factors, those with 4-5 favorable lifestyle factors had a lower risk of overweight obesity and high blood pressure (<i>ARR</i>=0.84, 95%<i>CI</i>: 0.59-0.92). <b>Conclusion:</b> Boys aged 9-18 in Tianjin are more prone to multimorbidity of overweight obesity and high blood pressure, overweight obesity and myopia, and overweight obesity with high blood pressure and myopia. Children and adolescents with 4-5 favorable lifestyle factors have a reduced risk of occurrence of overweight obesity and high blood pressure. Lifestyle has cumulative effects on multimorbidity of overweight obesity and high blood pressure.