Context: Most individuals who react to peanuts do so on their first known exposure. A potential but unproven route of occult exposure resulting in sensitization to peanut is via breast milk during lactation.
Objective: To investigate the ability of maternal dietary peanut protein to pass into breast milk during lactation.
Design and setting: Clinical investigation conducted at 2 North American hospitals from March 1999 to October 2000.
Patients: Twenty-three healthy, lactating women aged 21 to 35 years.
Intervention: Each woman consumed 50 g of dry roasted peanuts, after which breast milk samples were collected at hourly intervals.
Main outcome measures: Presence in breast milk of total peanut protein, analyzed by a sandwich enzyme-linked immunosorbent assay, and 2 major peanut allergens, Ara h 1 and Ara h 2, detected by immunoblot analysis.
Results: Peanut protein was detected in 11 of 23 subjects. It was detected in 10 subjects within 2 hours of ingestion and in 1 subject within 6 hours. The median peak peanut protein concentration in breast milk was 200 ng/mL (mean, 222 ng/mL; range, 120-430 ng/mL). Both major peanut allergens Ara h 1 and Ara h 2 were detected.
Conclusions: Peanut protein is secreted into breast milk of lactating women following maternal dietary ingestion. Exposure to peanut protein during breastfeeding is a route of occult exposure that may result in sensitization of at-risk infants.