Celiac disease (CD) is a chronic autoimmune condition where consuming gluten triggers an immune response that damages the lining of the small intestine. Lactose intolerance (LI) is the inability to fully digest lactose, the sugar found in milk, due to a lack of the enzyme lactase. These two distinct conditions are often found together, especially when celiac disease is newly diagnosed. Celiac disease can cause lactose intolerance because the intestinal damage directly impairs the body’s ability to process milk sugar. This connection means an individual may experience symptoms from both conditions simultaneously.
How Celiac Disease Damages Lactase Production
The lining of the small intestine contains millions of tiny, finger-like projections called villi, which are responsible for nutrient absorption. Celiac disease causes an inflammatory reaction to gluten, leading to the flattening and destruction of these villi, a process known as villous atrophy. This damage significantly reduces the surface area available for digestion and absorption.
The lactase enzyme, required to break down lactose into smaller, absorbable sugars, is located primarily on the tips of these villi. When the villi are damaged, the body loses the primary sites where this enzyme is produced. This results in a substantial decrease in lactase activity, leading to secondary lactose malabsorption.
Because the undigested lactose cannot be absorbed, it continues into the large intestine. There, bacteria ferment the sugar, producing excess gas and fluid. This fermentation process causes uncomfortable digestive symptoms like bloating, gas, abdominal cramps, and diarrhea, which are characteristic of lactose intolerance.
Confirming Secondary Lactose Intolerance and Its Prognosis
The lactose intolerance experienced by individuals with untreated celiac disease is classified as secondary, meaning it is a consequence of another underlying disease. This differs from primary lactose intolerance, which is a common, genetically programmed reduction in lactase production that occurs naturally with age.
Diagnosis of secondary lactose intolerance often follows the confirmation of celiac disease, especially if symptoms persist after removing gluten. The hydrogen breath test is a common method used to confirm lactose malabsorption. The patient drinks a lactose solution, and the test measures hydrogen gas in the breath, a byproduct of bacterial fermentation of undigested lactose in the colon.
The prognosis for secondary lactose intolerance is positive because the underlying cause is reversible. Once a person adheres strictly to a gluten-free diet, the small intestinal lining begins to heal, and the villi start to regenerate. As the villous structure returns, lactase production is restored, and the ability to digest lactose improves.
While primary lactose intolerance is permanent, the secondary form is typically temporary. The time it takes for lactase activity to normalize varies, but many patients see a regression of lactose malabsorption within a few months to a year of starting the gluten-free diet. A follow-up breath test can confirm that intestinal healing has successfully restored lactose digestion.
Managing Diet Through Recovery
Managing the diet involves addressing both the autoimmune condition and the temporary digestive issue. The long-term treatment for celiac disease is a strict, lifelong gluten-free diet (GFD), which enables the small intestine to heal and resolves the secondary lactose intolerance.
While the small intestine is recovering, temporary lactose restriction is often necessary to alleviate symptoms. This involves avoiding or significantly limiting foods high in lactose, such as milk and ice cream. For some, even small amounts of lactose can trigger symptoms until the gut lining is fully repaired.
Alternative products can help ensure adequate nutrition during this period. Lactose-free milk and dairy alternatives, such as soy or almond milk, provide calcium and other nutrients without the sugar. Additionally, naturally low-lactose products like hard cheeses and yogurt with live cultures are often better tolerated.
Lactase enzyme supplements, available in tablet form, can be used to break down lactose in dairy products before they reach the small intestine. This offers a temporary solution for those who wish to consume small amounts of lactose while healing. Most medical guidance suggests slowly reintroducing lactose-containing foods after several months of a strict GFD, allowing the patient to test their restored tolerance.