Changes in overweight/obesity and central obesity status from preadolescence to adolescence: a longitudinal study among schoolchildren in Japan

Background: Little is known about changes in overweight/obesity and central obesity status among schoolchildren from preadolescence to adolescence in Japan, where waist circumference (WC) is generally not measured in annual health examinations at elementary and junior high schools. This study examined changes of overweight/obesity and central obesity status among schoolboys and schoolgirls from preadolescence to adolescence in Japan. Methods: Study subjects were fourth-grade school children (9 or 10years of age) from all four of Ina town's elementary schools in Japan. Measurement of each participant's height, weight, and WC were made at baseline and 3years later. Childhood overweight/obesity was determined according to the age- and sex-specific body mass index cut-off points proposed by the International Obesity Task Force. Central obesity was defined as waist-to-height ratio >= 0.5. Kappa (kappa) statistic was calculated to examine the tracking of overweight/obesity and central obesity. Results: Data from 1436 participants (boys: n=720, girls: n=716) were analyzed. Overweight/obesity status tracked substantially from fourth grade to seventh grade in both boys (kappa=0.614, P value < 0.001) and girls (kappa=0.619, P value < 0.001). Among participants who were overweight/obese in fourth grade, 55.2% of boys and 63.2% of girls were still overweight/obese in seventh grade. Tracking of central obesity from fourth graders to seventh graders was substantial in boys (kappa=0.651, P value < 0.001) and moderate in girls (kappa=0.544, P value < 0.001). Among participants who had central obesity in fourth grade, 54.1% of boys and 52.6% of girls still had central obesity in seventh grade. Conclusions: The present study showed that the tracking of overweight/obesity from preadolescence to adolescence was substantial in boys and girls. Moreover, more than half of those who had central obesity in preadolescence had central obesity in adolescence. This study suggests that it is important to implement a primary prevention program for overweight/obesity and central obesity in elementary schools before fourth grade.