Lactose intolerance (patient information)

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Lactose intolerance


What are the symptoms?

What are the causes?

Who is at highest risk?


When to seek urgent medical care?

Treatment options

Where to find medical care for Lactose intolerance?

What to expect (Outlook/Prognosis)?

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mahda Alihashemi M.D. [2]


Lactose is a type of sugar found in milk and other dairy products. An enzyme called lactase is needed by the body to digest lactose. Lactose intolerance develops when the small intestine does not make enough of this enzyme. People sometimes confuse lactose intolerance with cow’s milk intolerance because the symptoms are often the same. However, lactose intolerance and cow’s milk intolerance are not related. Being intolerant to cow’s milk is an allergic reaction triggered by the immune system. Lactose intolerance is a problem caused by the digestive system.

What are the symptoms of Lactose intolerance?

Symptoms often occur 30 minutes to 2 hours after having milk products. Symptoms may be worse when you consume large amounts.

Symptoms include:

What causes Lactose intolerance?

.Babies' bodies make the lactase enzyme so they can digest milk, including breast milk.

  • Babies born too early (premature) sometimes have lactose intolerance.
  • Children who were born at full term often do not show signs of the problem before they are 3 years old.

Lactose intolerance is very common in adults. It is rarely dangerous. About 30 million American adults have some degree of lactose intolerance by age 20.

  • In white people, lactose intolerance often develops in children older than age 5. This is the age when our bodies may stop making lactase.
  • In African Americans, the problem can occur as early as age 2.
  • The condition is very common among adults with Asian, African, or Native American heritage.
  • It is less common in people of northern or western European background, but still may occur.

An illness that involves or injures your small intestine may cause less of the lactase enzyme to be made. Treatment of these illnesses may improve the symptoms of lactose intolerance. These may include:

Babies may be born with a genetic defect and are not able to make any of the lactase enzyme.

Who is at highest risk?

Between 30 and 50 million Americans are lactose intolerant and certain ethnic and racial populations are more affected than others. Up to 80 percent of African Americans, 80 to 100 percent of American Indians, and 90 to 100 percent of Asian Americans are lactose intolerant. The condition is least common among people of northern European descent.

Babies that are born prematurely are also more likely to be lactose intolerant, because lactase levels do not increase until the third trimester of a woman’s pregnancy.


Finding the cause of a food intolerance is not easy. There are various ways to diagnose lactose intolerance.

  • Elimination diet: This involves avoiding anything that contains lactose. If your symptoms improve, it is taken as an initial sign that you have lactose intolerance. You also keep a log of what you ate and any symptoms you had. Then a tolerance test is done. This test checks whether the symptoms return after you drink a lactose solution.
  • Hydrogen breath test: If the tolerance test results are inconclusive, the amount of hydrogen in your breath is measured before and after drinking a lactose solution. When lactose is broken down by bacteria in the large intestine, hydrogen is produced as a byproduct. The hydrogen is released into the bloodstream through the walls of the intestine and ends up being breathed out once it reaches the lungs. So people with lactose intolerance generally have more hydrogen in their breath. The test solution for adults contains 50 mg of lactose in 0.4 liters of fluid and is taken on an empty stomach. The breath test is repeated every 15 to 30 minutes for at least two or three hours. But smoking, chewing gum, poor oral hygiene and other factors can influence the results of the test. That is why it is important to check whether the lactose solution also causes typical lactose intolerance symptoms like bloating and diarrhea. If not, then higher hydrogen levels are likely to be caused by something else.
  • Lactose intolerance test: This test measures blood sugar levels after drinking a lactose solution. If blood sugar does not rise significantly it is a sign that you have lactose intolerance. This is because the body cannot absorb the sugar molecules when there is not enough lactase in the large intestine to break down lactose. The test solution for adults contains about 50 grams of lactose and is also taken on an empty stomach. Blood sugar levels are measured regularly over the next two hours. It is important to watch out for symptoms like diarrhea or cramps during this test as well.

When to seek urgent medical care?

Lactose intolerance is not serious.

Call your provider if:

  • You have an infant younger than 2 or 3 years old who has symptoms of lactose intolerance.
  • Your child is growing slowly or not gaining weight.
  • You or your child has symptoms of lactose intolerance and you need information about food substitutes.
  • Your symptoms get worse or do not improve with treatment.
  • You develop new symptoms.

Treatment options

Cutting down your intake of milk products that contain lactose from your diet most often eases symptoms. Also look at food labels for hidden sources of lactose in nonmilk products (including some beers) and avoid these.

Most people with low lactase level can drink up to one-half cup of milk at one time (2 to 4 ounces or 60 to 120 milliliters) without having symptoms. Larger servings (more than 8 ounces or 240 mL) may cause problems for people with the deficiency.

Milk products that may be easier to digest include:

  • Buttermilk and cheeses (these foods contain less lactose than milk)
  • Fermented milk products, such as yogurt
  • Goat's milk
  • Ice cream, milkshakes, and aged or hard cheeses
  • Lactose-free milk and milk products
  • Lactase-treated cow's milk for older children and adults
  • Soy formulas for infants younger than 2 years
  • Soy or rice milk for toddlers

You can add lactase enzymes to regular milk. You can also take these enzymes as capsules or chewable tablets. There are also many lactose-free dairy products available.

Not having milk and other dairy products in your diet can lead to a shortage of calcium, vitamin D, riboflavin, and protein. You need 1,000 to 1,500 mg of calcium each day depending on your age and gender. Some things you can do to get more calcium in your diet are:

  • Take calcium supplements with Vitamin D. Talk to your healthcare provider about which ones to choose.
  • Eat foods that have more calcium (such as leafy greens, oysters, sardines, canned salmon, shrimp, and broccoli).
  • Drink orange juice with added calcium.

Where to find medical care for Lactose intolerance?

Directions to Hospitals Treating Lactose intolerance


There is no known way to prevent lactose intolerance. You can prevent symptoms by avoiding foods with lactose.

What to expect (Outlook/Prognosis)?

Symptoms most often go away when you remove milk, other dairy products, and other sources of lactose from your diet. Without dietary changes, infants or children may have growth problems.

Possible Complications

Common complications of lactose intolerance if they do not intake adequate quantities of dairy products and calcium include:


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