Background: Cow's milk proteins secreted in human milk may cause cow's milk allergy (CMA) even during exclusive breast-feeding. We studied beta-lactoglobulin levels in human milk of mothers of infants with CMA. We also studied intestinal absorption of macromolecules in the same mothers to see whether it is related to the secretion of beta-lactoglobulin in human milk.
Methods: CMA was verified with oral challenge in 46 of 55 infants assessed. beta-Lactoglobulin levels were assessed in human milk from 53 of 55 mothers of the infants before (basal sample) and 1 and 2 hours after an oral cow's milk load, which was given after a 24-hour milk-free diet. beta-Lactoglobulin was determined by an ELISA with a detection limit of 0.002 microgram/L. The 6-hour urine recovery of a high-molecular-weight polyethylene glycol (PEG) 3000 was assessed after an oral load of PEG in 45 of 55 mothers.
Results: beta-Lactoglobulin was found in the 1- or 2-hour samples in 75% of the mothers. beta-Lactoglobulin levels were increased in the 1- or 2-hour samples as compared with the basal levels in about half of the mothers. The respective levels were decreased in one third of the mothers whose basal beta-lactoglobulin levels were higher than in the others. beta-Lactoglobulin was found in none of the three human milk samples in 15% of the mothers. After an oral load of a high-molecular-weight PEG 3000, the 6-hour urine recovery of PEG was similar in the mothers of the infants with CMA and the mothers of infants without CMA. Neither was the urinary recovery of PEG related to the beta-lactoglobulin levels in human milk.
Conclusions: The results support the view that beta-lactoglobulin in human milk may contribute to, but does not alone explain, the development of CMA in breast-fed infants.