Obesity in children is a serious public health problem in Japan. However, the prevalence of central fatness has not been well determined in Japanese youth. We studied the relationship between body mass index (BMI) and waist circumference (WC) using line of equality analysis in 5,787 boys and 4,639 girls aged 6 to 17 years who participated in the 1992–1994 national survey on body sizes. WC was measured at the level of maximum waist narrowing in girls (WC1) and at the level of the top of iliac crest in boys (WC2). Using the 1978–1981 national survey data as baseline reference, excess fatness was defined as measurements exceeding the 90th centile in WC or in BMI. Among boys, 2,466 (42.6%) had WC2 >90th centile and 1,029 (17.8%) BMI >90th centile; whereas among girls, 895 (19.3%) had WC1 >90th centile and 673 (14.5%) BMI >90th centile. WC2-standard deviation scores (SDS) exceeded BMI-SDS in 5,060 (87.4%) boys and WC1-SDS exceeded BMI-SDS in 3,168 (68.3%) girls, respectively. Our results suggested a much higher prevalence of central fatness than generally recognized for Japanese children and adolescents, in particular, in Japanese boys.
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