Does breastfeeding protect against childhood overweight? Hong Kong's 'Children of 1997' birth cohort

Background: Observational studies from mainly Western settings suggest breastfeeding may protect against childhood adiposity; however, breastfeeding and adiposity share social patterning potentially generating confounding, making evidence from other settings valuable. Methods: We used multivariable linear regression to examine the prospective adjusted associations of breastfeeding with body mass index (BMI), height and weight z-scores at 7 years of age relative to the 2007 World Health Organization (WHO) growth reference, in a large (n = 8327), population-representative Hong Kong Chinese birth cohort, recruited between April and May 1997 with high follow-up (n = 7026). Results: Low socio-economic position (SEP) was associated with never breastfeeding and with exclusive breastfeeding for ≥3 months. We did not find any association between breastfeeding and BMI [z-score mean difference 0.07, 95% confidence interval (CI) -0.05 to 0.19], height (0.02, 95% CI -0.07 to 0.11) or weight (0.07, 95% CI -0.05 to 0.18), adjusted for sex, birth weight, gestational age, SEP, second-hand smoke (SHS) exposure, parity, mother's age at birth, mother's place of birth and serious infant morbidity. Conclusions: In a non-European setting, breastfeeding was not associated with child adiposity, suggesting that observed protective effects may be due to socially patterned confounding by SEP, maternal adiposity and maternal smoking.