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.