Table 1.

Recommendations for future research on breastfeeding and asthma in new studies or using existing datasets.

Domain	Recommendations
Study design	Ideally, recruit prenatally and follow prospectively
Breastfeeding exposures	Essential: capture exclusivity and duration, and evaluate dose effects: breastfeeding duration as a continuous measurement duration of exclusive breastfeeding duration of any breastfeeding Ideally, define using international criteria [29] and distinguish between: feeding at the breast versus bottled breast milk donor human milk versus mother’s own milk mixed feeding with formula versus solid foods relative proportion of breast milk versus other nutrition
Asthma outcomes	Define using international criteria [38,110]. Ideally, use objective physician diagnosis and capture pulmonary function. Also consider: asthma phenotypes (e.g., atopic versus non-atopic) age of onset (diagnosis is uncertain before age 5)
Confounding	Adjust for essential confounders socioeconomic status maternal smoking gestational age Consider additional approaches to address confounding sibling controls Mendelian randomization cross-cohort comparisons
Effect Modifiers	Test for interactions or conduct stratified analyses by: maternal asthma maternal and infant genetics infant sex microbiota-disrupting factors (c-section, antibiotics) preterm birth exposure to smoke/pollution
Reverse causality	Conduct sensitivity analyses excluding infants with asthma symptoms prior to weaning.
Mechanistic studies	Use biological specimens or pre-clinical models to study causal pathways identified in clinical studies epigenetics bioactive components of human milk (integrated multi-omic approaches) immunity microbiota lung growth
Generalizability	Consider and comment on generalizability of results based on study population and setting (e.g., breastfeeding rates, policies and culture; asthma prevalence)