Concentration of food allergens in breastmilk and association with maternal factors– A systematic review

Common food allergens have been detected in breast milk with wide inter-individual variations in concentrations. As maternal factors, such as age, smoking, and body mass index have been associated with breast milk composition, we aimed to identify maternal characteristics associated with the concentration of food allergens in breast milk. A PROSPERO (CDR42024558231) registered systematic review search was conducted in MEDLINE, EMBASE, Cochrane Library, CINAHL and Scopus until March 10th, 2025. Article inclusion criteria were human studies, where participants consumed a standardized amount of a common food allergen prior to breast milk sampling, and the concentration of that food allergen was measured in their breast milk. Seventeen articles were included in the systematic review. Despite a standardized amount of food allergen consumption, large inter-individual variations were reported in food allergen breast milk concentrations. Maternal allergic disease (four studies), amount of the food allergen typically eaten by the mother (two studies), stage of lactation (one study) and mammary epithelium permeability (one study) were the only maternal factors examined. No studies reported significant associations between these maternal characteristics and food allergen breast milk concentrations. No previous studies have been specifically designed to determine whether maternal characteristics are associated with food allergen breast milk concentrations. We therefore remain unable to explain large variations in inter-individual food allergen breast milk concentrations. New adequately powered studies are needed to investigate associations with maternal factors previously found to influence breast milk composition, such as age, smoking, body mass index and stage of lactation.