Furthermore, later studies using the humanized UGT1 mouse model have clarified that breast milk reduced the expression of intestinal UGT1A1, which enhanced the risk of hyperbilirubinemia because UGT1A1 expression in the small intestine played an important role in bilirubin glucuronidation during the neonatal period [27, 28]. This evidence concerns the gene UGT1A1 and Hyperbilirubinemia.