Breastfeeding and overweight: longitudinal analysis in an Australian birth cohort.

OBJECTIVE To examine adiposity in relation to breastfeeding using longitudinal analysis in an Australian birth cohort. STUDY DESIGN Repeated surveys from 16 weeks gestation to 8 years in a cohort (N = 2087) recruited through antenatal clinics. Overweight was defined by National Center for Health Statistics 95th percentiles for weight-for-length at 1 year and body mass index (BMI) at 3, 6, and 8 years. Overweight was examined using Generalized Estimating Equations with results summarized as OR. BMI Z scores were analyzed in mixed models. RESULTS At 1 year, infants breastfed >12 months were the leanest group (mean Z score -0.16, 95% CL -0.28, -0.04; not breastfed 0.16, 95% CL 0.02, 0.29; breastfed < or = 4 months 0.31, 95% CL 0.22, 0.40; 5-8 months 0.17, 95% CL 0.06, 0.27; 9-12 months 0.11, 95% CL 0.01, 0.22). From 1 to 8 years, children breastfed < or = 4 months had the greatest risk of overweight (OR 1.29, 95% CL 0.89, 1.97) and the highest prevalence of maternal obesity, smoking, and lower education. CONCLUSIONS Infants breastfed >12 months were leaner at 1 year but not at 8 years. Breastfeeding < or = 4 months was associated with greatest risk of overweight and adverse maternal lifestyle. Familial factors may modify associations between breastfeeding and adiposity beyond infancy.