Sex differences in obesity incidence: 20-year prospective cohort in South Africa

Background: Prospective data spanning childhood and adolescence are needed to better understand obesity incidence among children and to identify important periods for intervention. Objective: To describe gender differences in overweight and obesity from infancy to late adolescence in a South African cohort. Methods: We analysed body mass index at 1-2 years, 4-8 years, 11-12 years, 13-15 years and 16-18 years among 1172 participants in the South African Birth-to-Twenty cohort. Results: Among boys, overweight and obesity prevalence declined from age 1-2 years to 16-18 years. Among girls, overweight and obesity prevalence increased from 4-8 years to 16-18 years. Obesity incidence was highest from 4-8 years to 11-12 years in boys (6.8 cases per 1000 person-years) and from 11-12 years to 13-15 years in girls (11.2 cases per 1000 person-years). Among girls, obesity at 16-18 years was associated with overweight (odds ratio [OR] = 3.6; 95% confidence interval [CI] 1.8-7.2) or obesity (OR = 8.0; 95% CI 3.7-17.6) at 1-2 years and overweight (OR = 6.8; 95% CI 3.3-13.9) or obesity (OR = 42.3; 95% CI 15.0-118.8) at 4-8 years; for boys, obesity at 16-18 years was associated with overweight at 1-2 years (OR = 5.6; 95% CI 1.7-18.0) and obesity at 4-8 years (OR = 19.7; 95% CI 5.1-75.9). Conclusions: Among girls, overweight and obesity increased throughout childhood. Overweight and obesity were not widely prevalent among boys. Early childhood and post-puberty may be important periods for intervention among girls.