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Lactose Intolerance

Lactose Intolerance

Alternate Names

  • lactase deficiency


Lactose intolerance is a condition in which a person cannot digest enough lactose, the sugar found in milk and milk products. The individual has a deficiency of an enzyme known as lactase.

What is going on in the body?

People with lactose intolerance do not have enough lactase to break down the lactose they eat or drink. They are unable to break the lactose down into glucose, which is the form of sugar used by body cells.
When lactase is missing from the intestine, the condition is called lactase deficiency. There are three types of lactase deficiency:
  • congenital
  • acquired
  • temporary
Congenital lactase deficiency is a rare disorder that appears to run in families. Infants begin to have symptoms of bloating and watery diarrhea shortly after starting on breast milk or formula feeding.
Acquired lactase deficiency comes on gradually as a person ages. This form of the condition also seems to run in families, and affects certain ethnic groups more than others.
Temporary lactase deficiency sometimes follows gastroenteritis in children. When the child has diarrhea, his or her intestines are stripped of the enzyme lactase. The child then has trouble digesting lactose when he or she drinks milk products. When lactose is not digested, water is retained in the bowel. This results in bloating and watery diarrhea.
Lactose that passes into the large intestine is fermented by bacteria. This produces carbon dioxide, hydrogen, and methane. This in turn leads to bloating, cramping, and flatulence, or passing gas. The condition resolves once the intestinal cells have recovered.


What are the causes and risks of the condition?

Having no lactase causes lactose intolerance. In young children, temporary lactose intolerance may follow a stomach virus. About 75% of African Americans and Native Americans have lactose disorder. As many as 90% of Asian Americans are lactose-intolerant.
Milk and milk products are the only natural sources of lactose. However, dry milk powder, whey, curds, and milk solids are common ingredients in processed foods. Some foods that often contain lactose include:
  • baked goods, including bread
  • baking mixes for pancakes, cookies, and cakes
  • candy
  • cereals
  • instant soups and drinks
  • lunch meat
  • margarine and salad dressings
Lactose may also be found in both over-the-counter and prescription medicines. Common examples include antacids and oral contraceptives.


What can be done to prevent the condition?

There is no prevention for lactose intolerance. Individuals may reduce their symptoms by avoiding foods high in lactose. Lactose may be better tolerated if it is eaten with other foods or with a lactase supplement. Some lactose-containing foods are produced containing lactase.


How is the condition diagnosed?

Diagnosis of lactose intolerance begins with a medical history and physical exam. The healthcare professinal may order the following tests:
  • lactose tolerance test, which measures blood levels of glucose after a person has had a drink containing lactose
  • hydrogen breath test, which can detect increased levels of hydrogen gas produced by fermentation of lactose in the intestines and excreted through the lungs
  • stool acidity test, which measures acids found in stool when the lactose is not digested
In most cases, these tests are not required. If lactose intolerance is suspected, then milk and milk products can be eliminated from the diet for a period of time. If the symptoms go away, then lactose-containing foods should be added back into the diet to test whether lactose is the culprit.

Long Term Effects

What are the long-term effects of the condition?

In most cases, there are no long-term effects from lactose intolerance. However, an infant with congenital lactase deficiency can become very dehydrated and fail to thrive.

Other Risks

What are the risks to others?

Lactose intolerance is not contagious and poses no risk to others.


What are the treatments for the condition?

Infants and young children with lactose intolerance should not eat or drink foods containing lactose. These include milk and milk products. Special infant formulas are available for babies with congenital lactose intolerance. Older children and adults may be able to eat or drink limited amounts of lactose-containing foods.
The enzyme lactase is available in tablet, powdered or capsule form. Persons with lactose intolerance can sometimes tolerate milk products if they take a lactase tablet first. Liquid lactase may also be added to milk to lower the lactose content before the person drinks it. Some lactose-containing foods are produced containing lactase.
Dietary counseling can be helpful to an individual with lactose intolerance. The dietary plan should include foods high in calcium and vitamin D.

Side Effects

What are the side effects of the treatments?

Lactase supplements have no significant side effects.

After Treatment

What happens after treatment for the condition?

If the ability to digest lactose has been permanently lost, treatment might be lifelong.


How is the condition monitored?

Any new or worsening symptoms should be reported to the healthcare professional.

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