O B E S I T Y I N C H I L D H O O D : S E C U L A R T R E N D O R E P I D E M I C D I S E A S E ? span can be excluded. We conclude that the process of a secular trend is only ex-‐ pressed after birth. The assumption can be made that the intrauterine environment and the placental nutrition supply prevent the fetus from becoming overgrown. The two above-‐mentioned populations not only differ in time span but also in their socioeconomic background. The Kloosterman population concerned the low socio-‐ economic classes of Amsterdam6 in contrast to the Perinatreg study, which is na-‐ tionwide and includes all socioeconomic classes in the Netherlands7. For that rea-‐ son we compared two populations with the same socioeconomic background in the more homogeneous MUMC population. Besides, in this study group also length values were available so we could compare weight in relation to length. No differ-‐ ence was found between the measurements of weight and length neither in the interrelation between these two measurements, measured at birth in 1988 and 2007. Therefore, it is assumed that the socioeconomic differences between the two populations of Kloosterman and Perinatreg do not affect the results. Postnatal growth studies To evaluate a postnatal secular trend in weight and height, the growth curves from the studies by van Wieringen and Fredriks were compared8,9. Both height and weight were higher during the first years of life in the older study. An explanation could be that food composition for infants changed during the past 30 years10. The energy intake of the population of 1964 during the first three years of life exceeded the energy intake of the population of 1996 due to differences in feeding habits, while the energy expenditure is probably equal at this age. After the age of five years the energy expenditure is apparently decreased during the past 30 years. An explanation could be that energy expenditure is decreasing in childhood, for example because of lack of movement due to watching television or playing computer games. By analyzing the BMI, there is a remarkable increase of the BMI visible from the age of approximately five years. However, it has to be realized that the increase of the BMI is highly dependent on the increase of height*. As an example a ten years old boy is presented (Table 4) in which the BMI is calculated by the measures of height at a given percentile with corresponding weight. As is illustrated in Table 4, at the same age, the BMI varies widely depending on the height*. 35
Proefschrift binnenwerk Manon Ernst_DEF.indd
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