Lactose Intolerance

Lactose intolerance occurs when your small intestine doesn't produce enough of an enzyme (lactase) to digest milk sugar (lactose), a condition known as lactase deficiency. When this happens, the lactose doesn’t get broken down and absorbed in the small intestine. Instead, it passes into the colon, where it interacts with bacteria to cause gas, bloating, and diarrhea.

There are four types of lactose deficiency that can result in lactose intolerance:

The most common type is primary lactase deficiency, which causes a gradual decrease of lactase production over time. It typically begins in young children although the symptoms of lactose intolerance may not appear until late adolescence or adulthood. Scientists believe this type of lactase deficiency may be genetic.

Secondary lactase deficiency occurs due to an illness or injury that damages the small intestine, such as Crohn's disease, ulcerative colitis, celiac disease, gastroenteritis, chemotherapy, or intestinal surgery. It can usually be resolved by treating the underlying cause.

Some infants may be born with lactase deficiency. Developmental lactase deficiency occurs in premature babies and goes away shortly after birth. Congenital lactase deficiency is an extremely rare inherited disorder.

Symptoms of lactose intolerance typically occur 30 minutes to 2 hours after consuming milk or milk products. They include:

• Abdominal pain
• Diarrhea
• Gas and bloating
• Nausea

If your doctor suspects lactose intolerance based on your medical history, physical exam, and symptoms, he or she may order tests to confirm the diagnosis. For a lactose tolerance test, you will fast before you test and then drink a liquid that contains high levels of lactose. After two hours, a blood test will check for glucose in your bloodstream. If your glucose level doesn't rise, it means your body isn't producing enough lactase to properly digest and absorb lactose. For a hydrogen breath test, you will also drink a liquid that contains high levels of lactose. At regular intervals, you will breathe into a monitor to check for the presence of hydrogen, which is typically not detectable if your body is making lactase. If your body does NOT make enough lactase, undigested lactose will ferment in the colon, producing hydrogen and other gases. Increased levels of hydrogen in your breath indicate improper digestion of lactose. A stool acidity test is typically used for infants and children who can't undergo lactose tolerance or hydrogen breath tests. Undigested lactose also creates lactic acid and other acids that can be detected in a stool sample.

If you have primary or congenital lactase deficiency, you can’t increase the amount of lactase your body makes. However, there are a number of ways to manage lactose intolerance. You can simply avoid eating or drinking dairy products, limit the amount in your diet according to your symptoms, consume lactose-free or lactose-reduced milk and milk products, or use lactase products to break down the lactose in dairy products. Learn more about foods to avoid if you are lactose intolerant.