Different effects of living conditions on the variation in BMI and height in children before the onset of puberty

Abstract

Biological indicators of children's growth, such as the mean values for both height and weight, are often used as markers of change in living conditions. However, little is known about how the quality of life affects the variation in height and weight. Therefore, the aim of this study was to assess the variation in height and body mass index (BMI) in Polish children between 1966 and 2012. During this period, Poland underwent vast political and socioeconomic changes. The study included 5597 boys and 5479 girls aged 7-8 years of age. Socioeconomic status (SES) was defined in three categories: high, medium and low. Between 1966 and 2012, the mean values for height and BMI significantly increased in both sexes (P<0.001). The variation of these two parameters, however, showed a different pattern. Whereas the variation in Z-values for height remained unchanged in both sexes, the variation in BMI increased in boys (P<0.01) but not in girls. SES affected the variation in Z-BMI in 1978 in both sexes (P<0.001), whereas variation in Z-height between SES categories remained unchanged across all years of surveys in boys. Before the political transformation, significant regional differences were observed in the variances of Z-BMI (P<0.05) but not of Z-height. This pattern changed after the political transformation, when regional differences in variances of Z-BMI disappeared. It is concluded that the mean values and the variation of BMI are affected by a changing quality of life, whereas the variation in height is usually independent of living conditions.