Lactose Intolerance Forum
What is lactose intolerance?
Lactose intolerance is the inability to digest significant amounts of lactose, the major sugar found in milk. Lactose intolerance is caused by a shortage of the enzyme lactase, which is produced by the cells that line the small intestine. Lactase breaks down milk sugar into two simpler forms of sugar called glucose and galactose, which are then absorbed into the bloodstream. Not all people deficient in lactase have the symptoms commonly associated with lactose intolerance, but those who do are said to have lactose intolerance.
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?
People who do not have enough lactase to digest the amount of lactose they consume may feel very uncomfortable when they digest milk products. Common symptoms, which range from mild to severe, include nausea, cramps, bloating, gas, and diarrhea. Symptoms begin about 30 minutes to 2 hours after eating or drinking foods containing lactose. The severity of symptoms depends on many factors, including the amount of lactose a person can tolerate and a person’s age, ethnicity, and digestion rate.
How is lactose intolerance diagnosed?
Lactose intolerance can be hard to diagnose based on symptoms alone. People sometimes think they suffer from lactose intolerance because they have the symptoms associated with the disorder, not knowing other conditions such as irritable bowel syndrome can cause similar symptoms. A doctor can use tests to diagnose lactose intolerance but may first recommend eliminating cow’s milk from the diet to see if the symptoms go away.
The most common tests used to measure the absorption of lactose in the digestive system are the lactose tolerance, hydrogen breath, and stool acidity tests.
The Lactose Tolerance Test.
This test requires fasting (not eating) before the test and then drinking a liquid that contains lactose. Several blood samples are then taken over a 2-hour period to measure the person’s blood glucose (blood sugar) level. These measures indicate how well the body is able to digest lactose.
Normally, when lactose reaches the digestive system, the lactase enzyme breaks it down into glucose and galactose. The liver then changes the galactose into glucose, which enters the bloodstream and raises the person’s blood glucose level. If, however, lactose is incompletely broken down, the blood glucose level does not rise and a diagnosis of lactose intolerance is confirmed.
The Hydrogen Breath Test.
This test measures the amount of hydrogen in a person’s breath. Very little hydrogen is normally detectable. However, undigested lactose in the colon is fermented by bacteria and produces various gases, including hydrogen. The hydrogen is absorbed from the intestines, carried through the bloodstream to the lungs, and exhaled. In this test, the person drinks a lactose-loaded beverage and the breath is analyzed at regular intervals. Raised levels of hydrogen in the breath indicate improper digestion of lactose. Certain foods, medications, and cigarettes can affect the accuracy of the test and should be avoided before taking the test. People should check with their doctor to make sure they are not taking medications that may interfere with test results.
The lactose tolerance and hydrogen breath tests are not given to infants younger than 6 months of age. A large lactose load can be dangerous prior to this age, as infants are more likely to become dehydrated from diarrhea that can be caused by lactose intolerance.
Stool Acidity Test.
This test may be used for infants and young children to measure the amount of acid in their stool. Undigested lactose fermented by bacteria in the colon creates lactic acid and other fatty acids that can be detected in a stool sample. Glucose may also be present in the sample as a result of unabsorbed lactose in the colon.
What causes lactose intolerance?
Some causes of lactose intolerance are well known. Primary lactase deficiency is a condition that develops over time. After about age 2 the body begins to produce less lactase, though most people will not notice symptoms until they are much older.
Secondary lactase deficiency occurs when injury to the small intestine or certain digestive diseases reduce the amount of lactase a person produces. These diseases include celiac disease, inflammatory bowel disease, and Crohn’s disease.
Researchers have identified a genetic link for lactose intolerance. Some people are born with a likelihood of developing primary lactase deficiency because it has been passed to them genetically (inherited from their parents). This discovery may be useful in developing a diagnostic test to identify people with the condition.
Who is at risk for lactose intolerance?
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.
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