The relation between birthweight, childhood body mass index, and overweight and obesity in late adolescence: a longitudinal cohort study from Norway, The Tromsø Study, Fit Futures.

Objectives: Childhood overweight/obesity is associated with later overweight/obesity. However, the association between birth weight and later overweight/obesity has not been established. The aim of this study was to investigate the relation between both birth weight and childhood body mass index (BMI), and adolescent overweight/obesity in a Norwegian population.

Methods: The Tromsø Study - Fit Futures is a population-based cohort study conducted in 2010-2011 and 2012-2013 in Tromsø, Norway. A representative sample of 961 adolescents participated. Longitudinal anthropometric data were obtained from the Medical Birth Registry of Norway, childhood health records at 2-4 and 5-7 years of age, and repeated measurements at 15-18 and 18-20 years of age. Outcome was defined as normal weight (adult BMI <25 kg/m) or overweight/obese (adult BMI ≥2 5 kg/m) at 15-20 years of age according to international age- and sex-specific cut-off values for children. Associations were investigated using generalised estimating equations.

Results: In adjusted analyses, a 1-SD (586 g) higher birth weight was associated with a higher OR for overweight/obesity at 15-20 years of age (OR 1.25, 95% CI 1.06 to 1.48). Childhood BMI was also associated with overweight/obesity at 15-20 years of age: a 1-SD (1.35 kg/m) increase in BMI at age 2-4 years rendered an OR of 1.66 (95% CI 1.40 to 1.96); a 1-SD (1.83 kg/m) increase in BMI at age 5-7 years rendered an OR of 3.23 (95% CI 2.56 to 4.07). When compared with normal-weight children, those with severe overweight/obesity in childhood (adult BMI ≥27 kg/m) showed stronger associations with overweight/obesity at 15-20 years of age: OR 3.01 (95% CI 1.47 to 6.18) and OR 11.51 (95% CI 6.63 to 19.99) at ages 2-4 and 5-7, respectively.

Conclusion: Associations between birth weight and overweight/obesity at 15-20 years of age were modest, whereas the influence of BMI at 2-4 and 5-7 years on overweight/obesity at 15-20 years was moderate to strong.