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lactose intolerance

Alternative Names
lactase deficiency

Lactose intolerance is a condition in which a person cannot digest lactose. Lactose is the sugar found in milk.

What is going on in the body?
Lactose is a disaccharide, the primary sugar found in the milk of almost all mammals. The human intestine cannot absorb disaccharides unless they are broken down into simple sugars. This is done by intestinal enzymes. The enzyme that helps break down lactose is called lactase. When lactase is missing from the intestine, the condition is called lactase deficiency.

There are three types of lactase deficiency: congenital, acquired, and temporary.

Congenital lactase deficiency is a rare disorder that appears to run in families. Infants begin to have symptoms of bloating and watery diarrhoea shortly after starting breast milk or formula feeding. The digestion of other disaccharides, such as sucrose or maltose, is not affected.

Another type of lactase deficiency comes on gradually over time. It also seems to run in families. It affects certain ethnic groups more than others. The enzyme lactase is present in the human intestine from about the middle of pregnancy onward. The amount of lactase in the intestine begins to drop after weaning. By 5 to 7 years of age, a child's lactase activity is about 10% of what it was at birth.

Some people lose their ability to digest lactose or display some lactose deficiency. This varies by ethnic group. Between the ages of 19-61 years, about 19% Caucasian, 84% of Australian Aboriginals, 95% of Asians in Australia, and 90% of Chinese in Australia are lacking intestinal lactase.

Any disorder that affects the intestines can lead to a temporary deficiency of lactase. This commonly occurs after a bout of diarrhoea or viral gastroenteritis.

When lactose is not digested, water is retained in the bowel. This results in bloating and watery diarrhoea. 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 wind.

What are the signs and symptoms of the condition?
Lactose intolerance causes abdominal bloating and discomfort. It also produces watery diarrhoea and gas.

Infants with congenital lactase deficiency may have some of the following symptoms: These symptoms appear after breast milk or lactose-containing formula is introduced into their diet.

A temporary lactase deficiency sometimes follows an episode of viral gastroenteritis in children. When the child has diarrhoea his or her intestines are stripped of the enzyme lactase. The child then has trouble digesting lactose when he or she drinks milk products. This produces watery diarrhoea. This condition is only temporary.

What are the causes and risks of the condition?
Lactose intolerance is caused by a lack of lactase. In young children, temporary lactose intolerance may follow viral gastroenteritis.

What can be done to prevent the condition?
Persons can prevent the symptoms by avoiding foods high in milk content. Lactose may be better tolerated if it is eaten with other foods.

How is the condition diagnosed?
Several laboratory tests can help diagnose lactase deficiency by measuring the following:
  • the activity of lactase in a sample of intestinal lining
  • the acidity of diarrhoea in an infant or toddler
  • the level of glucose in the blood after ingesting milk
  • the level of hydrogen in a breath test after ingesting milk
  • the amount of lactose (disaccharide) in a specimen of faeces.
In most cases, such tests are not required. If a person's symptoms are felt to be due to lactose intolerance, 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 be sure that lactose was the culprit.

What are the long-term effects of the condition?
In most cases, there are no long-term effects.

An infant with congenital lactase deficiency can become very dehydrated and fail to thrive.

What are the risks to others?
Lactose intolerance is not contagious. Therefore, it poses no risk to others.

What are the treatments for the condition?
The treatment is to remove lactose and lactose-containing foods from the diet.

The enzyme lactase is available in tablet or capsule form. Persons with lactose intolerance can sometimes tolerate milk products if they take a lactase tablet first.

What are the side effects of the treatments?
There are no side effects to taking lactase.

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?
Doctors can be contacted regarding persistent problems related to lactose intolerance.

Author: John Wegmann, MD
Reviewer: HealthAnswers Australia Medical Review Panel
Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia
Last Updated: 1/10/2001
Potential conflict of interest information for reviewers available on request

This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.  All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.


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