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RESEARCH: Ikuko Funatogawa, Takashi Funatogawa, and Eiji Yano Do overweight children necessarily make overweight adults? Repeated cross sectional annual nationwide survey of Japanese girls and women over nearly six decades BMJ 2008; 337: a802 [Abstract] [Full text]

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factors contributing to obesity

Gydhia Zuhair AL-CHALABY   (2 September 2008)

Do overweight children necessarily make overweight adults? – possible biases due to cohort effects

C Mary Schooling, Gabriel M Leung   (3 September 2008)

factors contributing to obesity 2 September 2008
Gydhia Zuhair AL-CHALABY, F1 doctor pre-registration doctor Send response to journal: Re: factors contributing to obesity	No one can deny that obesity in children and teens can occur as a results of different combination of reasons, including enviromental factors, for instance, lack of exercise, excessive snacking, and family behaviour. Therefore, If the family started to pay more attention to the type of their child life style and decided to include more outdoor leisure activites and encourage the concept of a healthy diet, this can lead to decline in the percentage of overweight children and adults. As a result, I agree that there is no direct relation between being an overweight child and becoming an obese young adult as there are many key issues that might have a direct impact to determine that. Competing interests: None declared
Do overweight children necessarily make overweight adults? – possible biases due to cohort effects 3 September 2008
C Mary Schooling, Assistant Professor The University of Hong Kong, Pokfulam, Hong Kong SAR, Gabriel M Leung Send response to journal: Re: Do overweight children necessarily make overweight adults? – possible biases due to cohort effects	The data presented by Funatogawa et al show the secular trend in Japanese girls’, but not boys’, growth trajectory for body mass index.1 The pattern changed from older cohorts being relatively thin in childhood and then fatter in adulthood, to more recent cohorts being relatively fatter in childhood but thinner in adulthood. Hence, the authors argue, overweight children may not make overweight adults. This comparison across birth cohorts is invalid unless the pattern of growth and final body proportions is unchanged over calendar time, because the tempo of growth affects childhood body mass index and body mass index varies systematically with body proportions. However, there were secular trends towards a faster tempo of growth and final longer legged body proportions for Japanese girls in the mid 20th century.2 These secular trends bias the more recent female cohorts to look fatter in childhood as the authors explain “if the timing of growth is accelerated, the prevalence of obesity should increase in childhood’.1 Conversely, these trends also bias the more recent female cohorts to look thinner in early adulthood, because body mass index decreases as relative leg length increases, as illustrated in Figure 1, with a decrease of about 0.9 in body mass index per 0.01 increase in leg to height ratio.3 These two trends taken together inevitably result in higher childhood body mass index and lower adult body mass in succeeding cohorts, with a cross over at the completion of growth, but provide no information as to whether fat children become thin adults. These secular trends were not identical in Japanese boys during the same time period, where there was less change in the tempo of growth and little trend towards longer legged body proportions in more recent cohorts.2 Body mass index curves by cohort for Japanese boys were not presented by Funatogawa et al but do not show succeeding cohorts crossing from fatter to thinner at the completion of growth.1 These body mass index curves by cohort for Japanese boys should also have been presented, so that appropriate interpretations could be made. Schooling CM, assistant professor Leung GM, professor Department of Community Medicine and School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China Competing interests: none. 1 Funatogawa I, Funatogawa T, Yano E. Do overweight children necessarily make overweight adults? Repeated cross sectional annual nationwide survey of Japanese girls and women over nearly six decades. BMJ. 2008;337:a802. 2 Ali MA, Uetake T, Ohtsuki F. Secular changes in relative leg length in post-war Japan. Am J Hum Biol. 2000;12:405-416. 3 Norgan NG, Jones PR. The effect of standardising the body mass index for relative sitting height. Int J Obes Relat Metab Disord. 1995;19:206- 208. Competing interests: None declared