Temporal course of the development of obesity in Japanese school children: a cohort study based on the Keio Study

To demonstrate the temporal course of obesity development in Japanese school children by conducting a school-site cohort study over 12 years.

From 1981 to 1984, height and weight of 479 subjects (343 boys and 136 girls) were measured every year from entrance into primary school until graduation from high school in Tokyo. Obese children were defined as those with a body mass index (BMI) at or above the age-sex-specific standard value, derived from Japanese nationwide data.

Approximately 50% of the children who were obese in the primary school period were obese at age 17. Likewise, 40% who were obese in the junior high school period and 70% who were obese in the high school period were obese at age 17. Among 44 children who were obese at age 17, 14 showed tracking of obesity from the preschool period, 14 showed tracking from ages 7 to 11 years, 10 showed tracking from the junior high school period, and 6 showed tracking from the high school period.

Among children who were obese at age 17, most tracked from the primary school age or earlier. The earlier the tracking commenced, the greater the BMI at age 17. This indicates the importance of conducting health education for school children at an early age.