Lactose intolerance, also called lactase deficiency, means you aren’t able to fully digest the milk sugar (lactose) in dairy products. It’s not usually dangerous, but symptoms of lactose intolerance can be uncomfortable enough to steer you clear of the dairy aisles.

The problem behind lactose intolerance is a deficiency of lactase – an enzyme produced by the lining of your small intestine. Some people who think they are lactose intolerant actually don’t have impaired lactose digestion. And not everyone with low levels of lactase is lactose intolerant. Only people with low lactase levels and symptoms are considered to have lactose intolerance.

You can control symptoms of lactose intolerance through a carefully chosen diet that limits lactose without cutting out calcium, and possibly by taking supplements.

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.

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 Gets Lactose Intolerance?

A person may be or may become lactose intolerant for different reasons:

  • Ethnic background. People of Asian, African, Native American, and Hispanic backgrounds are more likely to develop lactose intolerance at a young age.
  • Other problems with the digestive tract. People with irritable bowel syndrome or Crohn’s disease have a reduced level of the lactase enzyme. Those with other diseases of the gastrointestinal tract, such as celiac disease, can also have problems digesting lactose.
  • Medications. Certain antibiotics can trigger temporary lactose intolerance by interfering with the intestine’s ability to produce the lactase enzyme.
  • Infection. After a bout of infectious diarrhea, some kids can develop a temporary lactose intolerance that usually improves after a few days or weeks.
  • Age. As people get older, their bodies usually stop producing the lactase enzyme, and most people will naturally become lactose intolerant over time.

Tests and diagnosis

Your doctor may diagnose lactose intolerance based on your symptoms and your response to reducing the amount of dairy foods in your diet. Your doctor can confirm the diagnosis by conducting one or more of the following tests:

  • Lactose tolerance test. You’ll need to avoid eating before this test, to ensure accurate results. Once at the doctor’s office, you’ll drink a liquid that contains high levels of lactose. When this lactose reaches your digestive system, the lactase enzyme normally breaks it down into glucose and galactose, which can be absorbed by your bloodstream. In this test, you’ll give blood samples over a two-hour period to measure your glucose level. If your glucose level isn’t rising, it means you aren’t properly digesting and absorbing the lactose-filled drink.
  • Hydrogen breath test. This test also requires you to drink a liquid that contains high levels of lactose. Then your doctor measures the amount of hydrogen in your breath at regular intervals. Normally, very little hydrogen is detectable. However, undigested lactose reaches your colon and ferments, causing hydrogen and other gases to be released, absorbed by your intestines, and eventually exhaled. Large amounts of exhaled hydrogen indicate that you aren’t fully digesting and absorbing lactose and that you’re probably intolerant.
  • Stool acidity test. Infants and children suspected of having lactose intolerance take a stool acidity test. The amount of lactose required for the lactose tolerance test or the hydrogen breath test may be dangerous for infants and children. The stool acidity test measures the amount of acid in the stool. Undigested and unabsorbed lactose ferments in the colon, creating lactic acid and other acids that can be detected in a stool sample.

What is hidden lactose?

Although milk and foods made from milk are the only natural sources of lactose, it is often added to prepared foods. People with very low tolerance for lactose should know about the many food products that may contain even small amounts of lactose, such as

  • bread and other baked goods
  • processed breakfast cereals
  • instant potatoes, soups, and breakfast drinks
  • margarine
  • lunch meats (other than kosher)
  • salad dressings
  • candies and other snacks
  • mixes for pancakes, biscuits, and cookies
  • powdered meal-replacement supplements

Some products labeled non-dairy, such as powdered coffee creamer and whipped toppings, may actually include ingredients that are derived from milk and therefore contain lactose.

Learn to read food labels with care, looking not only for milk and lactose, but also for words such as whey, curds, milk by-products, dry milk solids, and non-fat dry milk powder. If any of these words are listed on a label, the product contains lactose.

Lactose is also used in more than 20 percent of prescription drugs and about 6 percent of over-the-counter medicines. Many types of birth control pills contain lactose, as do some tablets for stomach acid and gas. However, these products typically affect only people with severe lactose intolerance.

Sources: Kids Health, Digestive

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