Intestinal permeability to intact lactose in newborns and adults.

Small amounts of lactose have been shown to be absorbed intact across the intestine and excreted unchanged in the urine of newborns and adults. We designed a study to quantitate the intestinal uptake and urinary excretion of this disaccharide in these age groups. Similar amounts of lactose were given orally to 17 term newborns (age: 24.8 +/- 3.0 h) as a standard infant formula, and to 15 adult lactose absorbers (age: 28.1 +/- 2.6 years) and 11 adult lactose malabsorbers (age: 24.7 +/- 2.9 years) as a 20% water solution. Following lactose ingestion, breath was collected every 30 or 60 min for 3 h and analyzed for hydrogen concentration. Urine was also collected, and lactose and creatinine concentrations were determined. Peak hydrogen concentration was less than 20 ppm above baseline in newborns and adult lactose absorbers and 85 +/- 14 ppm in adult lactose malabsorbers. Urinary lactose excretion, expressed as a function of body weight (mg/ml/kg b.w.), was substantially greater in newborns (4.2 +/- 0.82) than in adult lactose absorbers (0.29 +/- 0.07; p less than 0.001) and adult lactose malabsorbers (0.55 +/- 0.04; p less than 0.01). Similarly, urinary lactose excretion expressed as a ratio of urinary lactose to urinary creatinine (mg/mg) was increased (p less than 0.001) in newborns (2.05 +/- 0.26) when compared to adult lactose absorbers (0.11 +/- 0.02) and adult lactose malabsorbers (0.20 +/- 0.02). Our data demonstrate that the intestinal uptake and urinary excretion of intact lactose is significantly increased in newborns compared to adult subjects.