Lactose intolerance is the inability to digest lactose, a sugar found in milk and milk products. Lactose intolerance is caused by a deficiency of the enzyme lactase which is produced by the cells lining the small intestine. When a person is newly diagnosed with Celiac disease it is often discovered that they also have become lactose intolerant. The reason is that Celiac disease patients have damage to the mucosa (or lining) of their small intestine where lactase enzymes necessary to digest milk are produced. Fortunately, lactose intolerance usually is mitigated once the person removes gluten from their diet and the small intestinal health improves. This reduction in lactose intolerance symptoms can take anywhere from six months to two years. As a result, a group of Italian researchers believe Celiac patients should be tested using the Hydrogen Breath Test within a year of being gluten free. The gluten free diet may have helped improve their lactase production to the point where they no longer need to avoid dairy products.
Reference: Scandinavian Journal of Gastroenterology 2007; 5:14 “A regression of Lactose Malabsorption in Coeliac patients after receiving a gluten free diet”