Prevalence of early childhood obesity in Ireland: Differences over time, between sexes and across child growth criteria

Background: Various child growth criteria exist for monitoring overweight and obesity prevalence in young children. Objectives: To estimate early overweight and obesity prevalence in Ireland and compare the differences in prevalence across ages, growth criteria and sexes. Methods: Longitudinal body mass index data from the nationally representative Growing Up in Ireland infant cohort (n = 11 134) were categorized (‘under-/normal weight’, ‘risk of overweight’, ‘overweight’, ‘obesity’) using the sex- and age-specific International Obesity Task Force growth reference, World Health Organization growth standard and World Health Organization growth reference criteria. Differences in prevalences between criteria and sexes, and changes in each weight category and criterion across ages (9 months, 3 years, 5 years), were investigated. Results: Across criteria, 11%–40% of children had overweight or obesity at 9 months, 14%–46% at 3 years and 8%–32% at 5 years of age. Prevalence estimates were highest using the World Health Organization growth reference, followed by International Obesity Task Force estimates. Within each criterion, prevalence decreased significantly over time (p < 0.05). However, when combining both World Health Organization criteria, as recommended for population studies, prevalence increased, due to differences in definitions between them. Significantly more boys than girls had overweight/obesity using either World Health Organization criterion, which was reversed using the International Obesity Task Force growth reference. Conclusions: To increase transparency and comparability, studies of childhood obesity need to consider differences in prevalence estimates across growth criteria. Effective prevention, intervention and policy-making are needed to control Ireland's high overweight and obesity prevalence.