Month of birth and body height differences in Polish urban schoolchildren from Katowice

The present study is aimed at testing a hypothesis of a similar pattern of month-of-birth effect on body height in both Polish urban and rural populations. Height differences among 1599 subjects aged 5-18 years and born in various months of the year were analyzed. Urban children attending kindergartens, elementary and high schools in Katowice (an industrial region of southern Poland) between 1985-1987 were cross-sectionally examined. Individuals’ heights were z-scored according to sex and age against the Polish body height standards. The results obtained were then compared with those for the children from the Barciany commune in an agricultural region of northeastern Poland. The general pattern of annual differences resembled the one obtained for the population from Barciany. The relationship between month of birth and body height decreased with age. It was statistically significant in the group of pre-adolescent children and insignificant in the total sample. Environmental factors, such as temperature, insolation, humidity, and air pollution were considered as potentially modifying the pattern of seasonal changes in Katowice. In addition, the socio-economic status of the Upper Silesian population was also considered. The results obtained suggest a tendency toward seasonal differentiation of body height, though likely dampened by seasonal changes in air pollution and also by specific social and economic stratification of the Upper Silesian society.