Breath hydrogen excretion in normal newborn infants in response to usual feeding patterns: evidence for "functional lactase insufficiency" beyond the first month of life.

Sequential studies of morning breath hydrogen excretion were carried out in the homes of 16 normal breast-fed or formula-fed infants during the first 5 months of life. Except for two infants whose stools did not produce H2, all infants had elevated breath H2 excretion (greater than 10 parts per million) during and after the first month of life. There was a significant relationship to age (P less than 0.005) for all three measures of H2 excretion (4-hour average, peak, and preprandial), with mean values being highest in month 2, elevated but lower in month 1, and dropping significantly in months 3 and after. Additional 24-hour studies with six 7-week-old infants demonstrated that H2 excretion was inversely related to state of arousal, more likely to be detected in the afternoon, and not clearly related to time of feeding. These findings suggest that incomplete lactose absorption in response to usual feeding patterns persists beyond the first months of life in all infants. The pattern of breath H2 excretion indicates a probable developmental change in quantity and consistency of carbohydrate substrate delivered to colonic flora. Although elevated breath H2 excretion in response to normal feeding demonstrates incomplete absorption, it should not be used to determine an infant's status as a "lactose malabsorber."