Risk of overweight among adolescents who were breastfed as infants

Context Overweight during adolescence predicts short- and long-term morbidi ty as well as obesity in adulthood. The prevalence of overweight among adol escents is high and continues to increase. Physiological and behavioral mec hanisms and preliminary epidemiologic data suggest that breastfeeding could lower the risk of subsequent obesity in adolescence. Objective To examine the extent to which overweight status among adolescent s is associated with the type of infant feeding (breast milk vs infant form ula) and duration of breastfeeding. Design, Setting, and Subjects Survey of 8186 girls and 7155 boys, aged 9 to 14 years, who are participants in the Growing Up Today Study, a nationwide cohort study of diet, activity, and growth. In the fall of 1996 we mailed a questionnaire to each of the subjects, and in the spring of 1997, we mail ed a supplemental questionnaire to their mothers, who are participants in t he Nurses' Health Study II. Main Outcome Measure Overweight status defined as body mass index exceeding the 95th percentile for age and sex from US national data. Results In the first 6 months of life, 9553 subjects (62%) were only or mos tly fed breast milk, and 4744 (31%) were only or mostly fed infant formula. A total of 7186 subjects (48%) were breastfed for at least 7 months while 4613 (31%) were breastfed for 3 months or less. At ages 9 to 14 years, 404 girls (5%) and 635 boys (9%) were overweight. Among subjects who had been o nly or mostly fed breast milk, compared with those only or mostly fed formu la, the odds ratio (OR) for being overweight was 0.78 (95% confidence inter val [CI], 0.66-0.91), after adjustment for age, sex, sexual maturity, energ y intake, time watching television, physical activity, mother's body mass i ndex, and other variables reflecting social, economic, and lifestyle factor s. Compared with subjects who had been breastfed for 3 months or less, thos e who had been breastfed for at least 7 months had an adjusted OR for being overweight of 0.80 (95% CI, 0.67-0.96). Timing of introduction of solid fo ods, infant formula, or cow's milk was not related to risk of being overwei ght, Conclusion Infants who were fed breast milk more than infant formula, or wh o were breastfed for longer periods, had a lower risk of being overweight d uring older childhood and adolescence.