beta-Glucuronidase and hyperbilirubinaemia in breast-fed and formula-fed babies.

Breast milk or formula milk and serum samples from 34 breast-fed babies, 15 formula-fed babies, and their mothers were examined at 3 and 21 days of neonatal age. Infant faecal samples were obtained on day 21 only. At both ages serum total bilirubin concentrations were significantly higher in breast-fed than in formula-fed infants. Beta-glucuronidase activity in formula milk was negligible while that in human milk was considerable. Day 21 faecal beta-glucuronidase was higher in the breast-fed babies. In the breast-fed babies, serum bilirubin levels were related to concentrations of beta-glucuronidase in breast milk on both days 3 and 21 and to levels of faecal beta-glucuronidase on day 21. In 4 additional babies whose feeds were temporarily changed from breast milk to formula milk because of hyperbilirubinaemia there was a striking decrease in faecal beta-glucuronidase activity coincident with a fall in serum bilirubin. Breast milk beta-glucuronidase seems to be an important factor in the neonatal hyperbilirubinaemia of breast-fed babies.