Breastfeeding and Obesity Among Schoolchildren A Nationwide Longitudinal Survey in Japan

IMPORTANCE Although it is suggested that breastfeeding is protective against obesity in children, the evidence remains inconclusive because of possible residual confounding by socioeconomic status or children's lifestyle factors. Most of the participants in the previous studies were children in Western developed countries, so studies in a different context are awaited. OBJECTIVE To examine the associations of breastfeeding with overweight and obesity among schoolchildren in Japan, with adjustment for the potential confounders. DESIGN Secondary data analyses of a nationwide longitudinal survey ongoing since 2001, with results collected from 2001 to 2009. SETTING All over Japan. PARTICIPANTS A total of 43 367 singleton children who were born after 37 gestational weeks and had information on their feeding during infancy. EXPOSURES Five mutually exclusive infant feeding practice categories. MAIN OUTCOMES AND MEASURES Underweight, normal weight (referent group), overweight, and obesity at 7 and 8 years of age defined by using international cutoff points of body mass index by sex and age. RESULTS In multinomial logistic regression models with adjustment for children's factors (sex, television viewing time, and computer game playing time) and maternal factors (educational attainment, smoking status, and working status), exclusive breastfeeding at 6 to 7 months of age was associated with decreased risk of overweight and obesity compared with formula feeding. The adjusted odds ratios were 0.85 (95% CI, 0.69-1.05) and 0.55 (95% CI, 0.39-0.78) for overweight and obesity, respectively, at 7 years of age. Similar results were observed at 8 years of age. CONCLUSIONS AND RELEVANCE Breastfeeding is associated with decreased risk of overweight and obesity among schoolchildren in Japan. Therefore, it would be better to encourage breastfeeding even in developed countries.