Risk factors for childhood obesity: shift of the entire BMI distribution vs. shift of the upper tail only in a cross sectional study

Background: Previous studies reported an increase of upper body
mass index (BMI) quantiles for formula fed infants compared to
breastfed infants, while corresponding mean differences were low.
The aim of this study was to assess the impact of known risk
factors for childhood obesity on the BMI distribution. Methods:
Data on 4,884 children were obtained at obligatory school entry
health examinations in Bavaria (Germany). Exposure variables were
formula feeding, maternal smoking in pregnancy, excessive
TV-watching, low meal frequency, poor parental education, maternal
overweight and high infant weight gain. Cumulative BMI
distributions and Tukey mean-difference plots were used to assess
possible shifts of BMI distributions by exposure. Results: Maternal
overweight and high infant weight gain shifted the entire
BMI-distribution with an accentuation on upper quantiles to higher
BMI values. In contrast, parental education, formula feeding, high
TV consumption, low meal frequency and maternal smoking in
pregnancy resulted in a shift of upper quantiles only. Conclusion:
The single shifts among upper parts of the BMI distribution might
be due to effect modification of the corresponding exposures by
another environmental exposure or genetic predisposition. Affected
individuals might represent a susceptible subpopulation of the
exposed.