Lactose Intolerance

What Is It?

Lactose intolerance is a common cause of abdominal cramping, bloating and diarrhea. This condition occurs when the body does not have enough of the intestinal enzyme lactase. The job of lactase is to break down lactose, the main sugar in milk. Once lactose is broken down into simpler forms of sugar, these simple sugars can be absorbed into the bloodstream.

In normal digestion, lactose is digested in the small intestine without the release of gas bubbles. When lactose can't be digested well, it passes into the colon. Bacteria in the colon break down some of the lactose, producing hydrogen gas. The remaining lactose also draws water into the colon. The extra gas and water result in symptoms, such as cramping, diarrhea, bloating and flatulence (gas).

Lactose intolerance usually is genetic (inherited). In many people of African or Asian descent, the body begins making less lactase around age 5. As many as 90% of people from some areas of Eastern Asia, 80% of American Indians, 65% of Africans and African-Americans, and 50% of Hispanics have some degree of lactose intolerance. In contrast, most Caucasians (80%) have a gene that preserves the ability to produce lactase into adulthood.

To continue reading this article, you must login.
  • Research health conditions
  • Check your symptoms
  • Prepare for a doctor's visit or test
  • Find the best treatments and procedures for you
  • Explore options for better nutrition and exercise
Learn more about the many benefits and features of joining Harvard Health Online »