Importance: Long duration of breastfeeding is known to reduce the frequency of infections and the risk of overweight, both of which are prevalent health problems among children, but the mechanisms are unclear.
Objectives: To test whether early-life antibiotic use in children prevents the beneficial long-term effects of breastfeeding on weight development and lifetime antibiotic use, and to investigate whether the duration of breastfeeding is associated with long-term microbiota development.
Design, setting, and participants: Retrospective cohort study, conducted from June 2015 to December 2015, of the association between the duration of breastfeeding and lifetime antibiotic use by children as well as body mass index (BMI; calculated as weight in kilograms divided by height in meters squared) z score in a cohort of 226 healthy children aged 2 to 6 years attending day care at the study area in northern Finland and participating in a probiotic trial from October 1, 2009, through April 30, 2010. Fecal microbiota composition analysis was performed in a subcohort of 42 of these children.
Exposures: Duration of breastfeeding and the number of different antibiotic courses purchased for the child.
Main outcomes and measures: The BMI z score, lifetime antibiotic use after weaning, and fecal microbiota composition.
Results: A total of 226 children (mean [SD] age, 55 [1.4] months; 54% male) were included in the study. Among the 113 children with no antibiotics before weaning, each month of breastfeeding decreased the mean number of postweaning antibiotic courses by 5% (95% CI, 2% to 8%; P = .001) and mean BMI z scores by 0.08 unit (95% CI, 0.04 to 0.11; P < .001). Among the 113 early-life antibiotic users, the effect of breastfeeding on postweaning antibiotic use was borderline significant (estimated 4% decrease per month; 95% CI, 0% to 7%; P = .04) and the effect on BMI z score disappeared (estimated 1% increase; 95% CI, -3% to 5%; P = .50). In the subcohort of 42 children with fecal microbiota composition analysis, the children with short breastfeeding duration (0-6 months) and no early-life antibiotic use or with long breastfeeding duration (8-16 months) and early-life use of antibiotics had a significantly lower abundance of Bifidobacterium (by 55%; 95% CI, 43% to 87%; P = .006; and 39%, 95% CI, 30% to 68%; P < .001, respectively) and Akkermansia (by 71%; 95% CI, 28% to 87%; P = .008; and 69%; 95% CI, 22% to 90%; P = .02, respectively) compared with those with long duration of breastfeeding and no early-life antibiotics.
Conclusions and relevance: Antibiotic use in a child during breastfeeding may weaken the beneficial effects of long breastfeeding duration. The results suggest that particularly the long-term metabolic benefits of breastfeeding are conveyed by the intestinal microbiota.