A social-ecological approach to examine body mass index during early childhood in Ireland

Background: Childhood overweight and obesity (OWOB) is associated with adult obesity (10) and ill-health (11); however the prevalence among young children in Ireland is unknown. For prevention programmes to target those children most in need, risk factors of OWOB and critical time points when these factors occur need to be identified. This thesis investigated in-depth the OWOB prevalence and risk factors among young children in Ireland.

Methods: A literature review was conducted to identify a suitable child growth criterion for young children in Ireland. Prevalence of OWOB was assessed through secondary analysis of the Growing Up in Ireland National Longitudinal Study of Children. Families in the nationally representative infant cohort were interviewed when the children were nine months (n=11,134), three years (n=9,793) and five years old (n=9,001). At all ages, standardised weight and length/height among other variables were collected from the children and their caregivers. Associations of explanatory variables with children’s OWOB were analysed using binary logistic regression, and with longitudinal changes in body mass index (BMI) using multilevel regression models.

Results: Using the World Health Organization growth standard and growth reference to define OWOB (using the 1-z-score threshold), 40.4% of the nine-month-old children had OWOB, 45.7% of the three-year-olds and 31.5% of five-year-olds. At all ages, high birth-weight-for-gestational-age, late birth and rapid infant weight gain were strongly related to OWOB and elevated BMI. At specific ages, caregiver OWOB and education, household income, family structure, ethnic background, geographic region, screen use, sleep duration, antibiotic use and childcare were also associated with OWOB and longitudinal changes in BMI.

Discussion: Biological, material and psychosocial factors contribute to the high prevalence of early childhood OWOB seen in Ireland and risk factors should be targeted simultaneously to lower OWOB levels. Prevention should start as early as possible and be maintained throughout the early childhood.