Children's BMI is strongly effected by family income at birth – but parental education is of major importance for the growing social gap up to 8 years of age

Background: The development of BMI in early childhood is dependent on socioeconomic factors. Our aim was to explore the impact of parental education level and family income for development of BMI from birth to 8 years age.Methods: 3018 children born in 1998–2006 from the IDEFICS study and register controls were included. Weight and height measurements from birth up to 8 years of age were obtained from the Child Health Services. Parental education and family disposable income, obtained from Statistics Sweden and the Medical Birth Register, were defined as high/low. Obesity was defined by WHO references. Confounders were sex and age of the child, parental origin, maternal smoking and maternal BMI.Results: At birth, the children’s mean BMI (SD) was lower in families of low vs. high income (13,74 (1,35) vs. 13,94 (1,36), p<0.0001). Results remained significant after adjusting for confounders. No differences in birth BMI were detected between children of low and high-educated parents (13,87 (1,37) vs. 13,83 (1,35), p=0.48). From 6 months onwards, children of low-educated parents showed higher mean BMI than children of high-educated. At 8 years, mean BMI in the low/high educated groups were 17.12 (2.44) and 16.38 (1.94), p<0.0001. Results remained significant after adjusting for confounders. Prevalence of obesity in the low and high-educated groups were 11% and 4,1%, p<0,0001. The difference in BMI at 8 years seen in the low/high income group disappeared after adjusting for confounders (17.5 vs. 17.6, p=0,63).Conclusion: Impact of family socioeconomic factors on children’s BMI differs by income and education. The effect of parental education becomes more evident by age up to 8 years of age. Interventions for healthy weight development must start very early in life.