What is lactose intolerance?
Lactose intolerance is the inability to digest lactose, the sugar primarily
found in milk and dairy products. It is caused by a shortage of lactase in the
body, an enzyme produced by the small intestine that is needed to digest
lactose. While lactose intolerance is not dangerous, its symptoms can be distressing.
What are the symptoms of lactose intolerance?
Symptoms of lactose intolerance occur when there is not enough lactase being
produced by the body to digest the lactose consumed. Symptoms of lactose
intolerance include nausea, cramps, gas, bloating, or diarrhea within 30 minutes
to 2 hours after consuming milk or dairy products. The severity of symptoms
varies, depending on the amount of lactose an individual person can tolerate.
Some people may be sensitive to extremely small amounts of lactose-containing
foods while others can eat larger amounts before they notice symptoms. Age and
digestion rate may influence how much lactose an individual may tolerate.
What causes lactose intolerance?
Some causes of lactose intolerance are known. Certain digestive diseases,
such as Crohn’s disease, ulcerative colitis, celiac sprue (an inherited disorder
affecting the lining of the small intestine), other inflammatory bowel diseases,
and injuries to the small intestine (surgery or trauma) may reduce the amount of
lactase available to process lactose properly. If the small intestine is
injured, lactose intolerance may be temporary, with symptoms improving after the
intestine has healed.
Who is affected by lactose intolerance?
For most people, lactose intolerance develops over time as the body produces
less lactase. It is estimated that 30 to 50 million Americans have some degree
of lactose intolerance. Certain racial and ethnic populations are more affected
than others, including 80% of African-Americans, Jews, Mexicans, and Native
Americans, as well as 90% of Asians.
How is lactose intolerance diagnosed?
The most common test for the diagnosis of lactase deficiency is the hydrogen
breath test. This test is done at an outpatient clinic or doctor’s office. In
practice, many doctors will ask patients who suspect they have lactose
intolerance to avoid milk and dairy products for one or two weeks to see if
their symptoms subside, and will then confirm the diagnosis with the hydrogen breath test.
The hydrogen breath test measures the amount of hydrogen in the breath after
drinking a lactose-loaded beverage. Undigested lactose in the colon is fermented
by bacteria and produces hydrogen and other gases. Hydrogen is absorbed, carried
by the blood to the lungs, and exhaled. Raised levels of hydrogen in the breath
within 90 minutes indicate improper digestion of lactose. This test has a 90%
sensitivity to determine lactose intolerance. Certain foods, medications, and
cigarettes can affect the test result, so the patient will be instructed to
avoid these prior to taking the test.