Trends in childhood obesity in Japan over the last 25 years from the National Nutrition Survey

Objective: To describe the 25-year changes in BMI (measured in kilograms per meters squared) and the prevalence of obesity in Japanese children with special reference to urban-rural differences. Research Methods and Procedures: We used the data sets from the cross-sectional annual nationwide surveys (National Nutrition Survey, Japan) conducted from 1976 to 2000 and comprising 29,052 boys and 27,552 girls between 6 and 14 years of age. We carried out the trend analyses with the data on sex and age groups and on residential areas according to the size of the municipality (metropolitan areas, cities, and small towns). Results: The mean (age-adjusted) BMI increased by +0.32 kg /m(2) per 10 years in boys and by +0.24 kg/m(2) per 10 years in girls, increases that were remarkable in small towns. The prevalence of obese boys and girls increased from 6.1% and 7.1%, respectively, in the time-period 1976 to 1980, to 11.1% and 10.2% in 1996 to 2000. The increasing trend was most evident in 9- to 11-year-old children of both sexes living in small towns, whereas no changes were observed in girls in metropolitan areas. Discussion: Our data clearly show increasing trends in obesity prevalence in Japanese school children. Degrees of the increasing trends, however, differed across sex and age groups and residential areas, demonstrating a particular phenomenon that girls in metropolitan areas were unlikely to become obese. These epidemiological aspects indicate the priorities for intervention in population strategies to control obesity in children.