The Association Between Duration of Breastfeeding and Childhood Asthma Outcomes

The purpose of this study was to examine the association between breastfeeding duration and the subsequent development of childhood asthma.

The study included maternal-child dyads drawn from 3 prospective pregnancy cohorts and child follow-up at 4 to 6 years of age. These cohorts included dyads from multiple US sites enrolled in the ECHO-PATHWAYS consortium cohorts: (1) Conditions Affecting Neurocognitive Development and Learning in Early Childhood study, (2) The Infant Development and Environment Study, and (3) the Global Alliance to Prevent Prematurity and Stillbirth.

Any and exclusive breastfeeding duration was determined using a questionnaire at approximately 4 to 6 years of age. The International Study of Asthma and Allergies in Childhood questionnaire and others were used to assess child wheeze and asthma outcomes. Child wheeze and asthma outcomes were categorized as (1) current wheeze, (2) ever asthma, (3) current asthma, and (4) strict current asthma. Covariates included maternal demographics and selected effect modifiers (maternal asthma, mode of delivery, child sex). Multivariable logistic regression was used to assess the association between breastfeeding duration (any and exclusive breastfeeding) and child wheeze and asthma outcomes, adjusted for covariates and effect modifiers.

The analysis included 2021 dyads. In unadjusted and multivariable analyses, breastfeeding duration was not associated with child wheeze and asthma outcomes. Longer duration of exclusive breastfeeding was associated with decreased odds of current asthma. When assessing for effect modification by maternal history of asthma, protective associations for any breastfeeding duration were found among mothers without asthma (adjusted odds ratio 0.58 [95% confidence interval, 0.37–0.92] for >6 months versus 0–2 months), but not among mothers with asthma. There was no statistically significant indication of effect modification by infant sex or mode of delivery.

This study found evidence for protective associations between longer duration of exclusive breastfeeding (≥2 months) and child asthma outcomes. Duration of any breastfeeding was not strongly associated with development of wheeze or asthma, apart from ever asthma.

Numerous studies and literature suggest that human breast milk plays a key role in disease prevention. This study accounted for potential effect modification by factors such as maternal asthma and found a protective association between duration of exclusive breastfeeding and childhood asthma outcomes in mothers without any history of asthma. Results of this study may be influenced by recall bias, and it does not account for other potential environmental confounders known to play a key role in asthma development, such as housing, secondhand smoke, or mold exposures. Future prospective studies are needed to further assess the role of breastfeeding duration in asthma development, while controlling for environmental factors.