What is Lactase Deficiency?

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  • Written By: D. Jeffress
  • Edited By: Jenn Walker
  • Last Modified Date: 18 November 2018
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Lactase deficiency is another term for lactose intolerance, a common disorder that causes problems digesting milk and other dairy products. The small intestine normally produces a large amount of lactase enzymes. The enzymes are needed to break down consumed lactose molecules into usable sugars before they reach the large intestine. If lactose is not metabolized correctly, a person can experience uncomfortable gas, bloating, diarrhea, and other digestive symptoms. There are no effective medical treatments for lactase deficiency, but people can usually prevent symptoms by avoiding large portions of dairy products and supplementing their diet with lactose-free milk and vitamins.

Since milk and dairy were not necessarily staples of the adult diet in the past, there was no evolutionary advantage for earlier humans to keep producing large amounts of lactase past infancy. The consequence today, when dairy products are consumed in bulk, is that many people develop some degree of lactase deficiency as they age. Lactose intolerance rarely affects infants and young children, though babies who are born prematurely are at an increased risk of congenital lactase deficiency. In addition, a severe illness that affects the stomach and intestines can cause a temporary case of lactose intolerance in an otherwise healthy person.


Symptoms of lactase deficiency tend to set in within an hour of consuming a large portion of dairy. The most common symptoms are gas, stomach cramps, and bloating. Some people experience episodes of diarrhea and nausea as well. A severe lactase deficiency can cause vomiting and flu-like symptoms. It is important to speak with a doctor if symptoms become a serious nuisance and do not seem to go away within a few hours of consuming dairy products.

A physician can usually diagnose a lactase deficiency simply based on the patient's reported symptoms. A breath hydrogen test may be used to confirm lactose intolerance and rule out other problems, such as inflammatory bowel disease. During the test, the patient is given a relatively small amount of lactose after avoiding all food and drink for several hours. The doctor collects breath samples over the course of about three hours to see if hydrogen levels rise, a sign that lactose is not being broken down properly in the intestines.

The best treatment for most cases of lactase deficiency is simply avoiding dairy. Patients with mild symptoms may still be able to enjoy dairy products, as long as they consume small, infrequent portions. There are many lactose-free foods and drinks that are specially designed to replace dairy for people with intolerance problems. A doctor may suggest taking calcium and vitamin D supplements when developing a new diet to make sure that nutritional needs are met.



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