Supplementation of vitamin D after birth affects body size and BMI in Polish children during the first 3.5 years of life - an analysis based on two cohorts measured in the years 1993-1997 and 2004-2008.

: The aim of this study was to assess whether the time of vitamin D supplementation after birth, season of birth and the type of feeding affected current body weight, body height and BMI among children aged 3-56 months from two cohorts. Additionally, it was analysed whether birth weight and birth length correlated with current BMI, body height and body weight in both cohorts of children. : The study material included 1930 children from the two cohorts, measured in two following periods: 1993-1997 and 2004-2008. Finally 849 healthy individuals aged 3-56 months were included in the analysis. Multiple stepwise regression model was applied to find the group of the most important variables explaining current body weight, body height and BMI. Moreover generalized linear models for two way interactions were used. : The season of birth, time of supplementation of vitamin D, but also birth weight and length might affect current body weight. Individuals' height could be associated with birth length and the season of birth. BMI value was probably regulated by birth length and weight. Furthermore, interactions between the time of vitamin D supplementation and season of birth and also between the time of vitamin D supplementation and type of feeding resulting in variation of body weight and BMI in the first years of life were also observed. : The study underlines the importance of a supplementation of vitamin D, season of birth and birth weight and length in current weight, height and body proportion in the first 3.5 years of life.