Influence of changes in lactase activity and small-intestinal mucosal growth on lactose digestion and absorption in preterm infants

Background: Feeding intolerance (ie, achieving and maintaining full enteral feedings) is a significant problem in preterm infants. A relation exists between feeding intolerance and incomplete lactose digestion. Objectives: We sought to identify the factors relating to lactose digestion and absorption, lactase activity, and small-intestinal mucosal growth. Design: Lactose digestion and absorption, lactase-specific activity, and lumen-to-mucosa water flux as a measure of small-intestinal mucosal surface area were determined by using the triple-lumen perfusion technique on 2 occasions 3 wk apart in 10 preterm infants (x +/- SEM gestational age: 28.0 +/- 0.2 wk). Results: Lactose digestion and absorption and lactase activity doubled between studies (P = 0.035 and P = 0.041, respectively). The change in digestion and absorption was related to lactase activity 2 (P = 0.034, R-2 = 0.38). Lactase activity correlated with gestational age at birth (P = 0.012, R-2 = 0.51). The number of days of feeding explained 80% of the variability in small-intestinal mucosal surface area (P = 0.001). Conclusions: To our knowledge, this is the first study to measure directly lactose digestion and absorption, lactase activity, and small-intestinal surface area in preterm infants. Changes in lactose absorption relate primarily to lactase activity rather than to mucosal growth. We showed directly a relation between enteral feeding and small-intestinal mucosal growth.