Social class variation in the predictors of rapid growth in infancy and obesity at age 3 years

OBJECTIVE: To examine the extent to which early child nutrition, maternal antenatal lifestyle behaviours and child diet and lifestyle explain social class inequalities in the risk of rapid weight gain between birth and 3 years and obesity at age 3 years. DESIGN: A longitudinal and prospective birth cohort study. SUBJECTS: Nationally representative sample of 11,134 children and their parents followed from 9 months of age until 3 years. Child weight and maternal height and weight were measured at 9 months and 3 years and child birth weight was extracted from hospital records. Other predictors of child growth and obesity were collected by maternal report at 9 months and 3 years. RESULTS: Although born lighter on average, children of unskilled manual parents were 274 g heavier than children of professional parents by 3 years of age. The fully adjusted model of rapid growth from birth to 3 years of age and obesity at 3 years of age accounted for all social class differentials. Breastfeeding and age at the introduction of solids were associated with the largest average reduction (41%) in the odds ratio (OR) of rapid growth in the first 9 months of life for each class relative to the professional class. In the period from 9 months to 3 years of age, the class differential in rapid growth was reduced most by measures of the child's diet and lifestyle. However, the impact of the groups of predictors varied by social class. For early life growth, among the non-manual classes the proportionate reductions are largest when adjusted for early infant nutrition, whereas maternal prenatal smoking is more important for the manual social classes. CONCLUSION: Preventative interventions to reduce levels of childhood obesity should be multi-dimensional but different dimensions should be given more or less significance depending on socio-economic group.