Abstract
The intestinal lactase activity in 6 newborn jaundiced light-treated infants with diarrhea and in 8 normal controls were compared by lactose tolerance test (LTT). The ability to hydrolyze lactose was minimal in the jaundiced infants during light-treatment compared to the controls which could absorb lactose very well. Peroral intestinal biopsies were taken from the newborn jaundiced infants during light-treatment. By histochemical technique no intestinal lactase activity was found in these intestines. When the jaundiced infants with diarrhea were given lactose-free diet, the stools normalized. The effect was reversed when breast milk was given while the baby was still jaundiced and light-treated. The increased amounts of unconjugated bilirubin in the intestine of jaundiced infants during light-treatment might inhibit the intestinal brush-border lactase. When the icterus fades the lactase is again active. The practical consequence is to give light-treated infants lactose-free diet if they get diarrhea, and to reintroduce breast milk or other lactose containing diet when the baby is no longer icteric.