Prevalence of lactose malabsorption in Japanese children and adults

The breath hydrogen test (BHT) was adapted for use in young infants and children. The diagnostic criterion of sugar malabsorption in the BHT was determined by oral administration of 0 5 g/kg of unabsorbable sugar (lactulose) to 21 healthy infants and children. A maximum increase in breath hydrogen >0 05 ml/min per m2 was observed in all subjects. A good correlation between results by the BHT and by the ordinary lactose tolerance test was obtained after oral administration of 2 g/kg lactose to 21 healthy infants and children, 2 congenital lactase-deficient infants, and 7 adults. Using this test, 80 healthy Japanese infants and children (aged between one month and 15 years) and 18 adults were examined for lactose malabsorption after a dose of 1 g/kg lactose. All infants and children under 2-years old absorbed lactose completely. The incidence of lactose malabsorption was 30 % in 3-year, 36 % in 4-year, 58 % in 5-year, and 86% in 6-year-old children, 85 % in schoolchildren, and 89 % in adults. Thus the incidence of lactase deficiency gradually increases with age from 3 years, and about 90 % of all normal Japanese adults are lactase-deficient.