Lactose Intolerance: What you need to know

What is lactose intolerance?

Lactose intolerance is the condition in which a person can't digest lactose, a disaccharide found in milk and milk products. The condition is caused by a deficiency of the enzyme known as lactase which is supposed to be produced by the cells lining the small intestine and break down lactose into two simple sugar called glucose and galactose, which are then absorbed into the bloodstream.

Note that lactose intolerance differs from milk allergy. The former does not involve any immune response while the latter does.  Allergy can trigger a life-threatening response while milk intolerance does not. Milk allergy occurs commonly in the first year of life while lactose intolerance occurs mostly in adulthood.

What causes lactose intolerance?

Lactose intolerance is caused by lactase deficiency. There are two types of lactose deficiency.

Primary lactase deficiency begins after about the age of 2 years when the body starts to produce less lactase. However, children are less likely to experience symptoms of lactose intolerance. The condition will become severe after a person gets into his late adolescence or adulthood.  

Secondary lactase deficiency is caused by some injury to the small intestine that occurs with severe diarrheal illness, celiac disease, Crohn’s disease, or chemotherapy. This type of lactase deficiency can occur at any age but is more commonly encountered in infancy.

Who is at risk for lactose intolerance?

Lactose intolerance is a condition commonly found among some ethnic and racial populations including African Americans, Hispanic Americans, American Indians, and Asian Americans and less commonly found among Americans of northern European descent.

Infants who are born prematurely are more likely to have lactose intolerance because lactase does not increase until the third trimester of pregnancy.

What are the symptoms of lactose intolerance?

Common symptoms including abdominal pain, abdominal bloating, gas, diarrhea, nausea among others may occur 30 minutes to 2 hours after ingesting of milk and milk products.  The severity varies with the individual and the amount of lactose ingested.

How is lactose intolerance diagnosed?

Because other conditions like irritable bowel syndrome can also cause similar symptoms, lactose intolerance is not easy to diagnose based on its symptoms.  

One simple test is to eliminate milk and milk products from one's diet and see what happens.  

Two other tests include hydrogen breath test, which detects high amounts of hydrogen in a patient who has lactose intolerance when he drinks milk, and stool acidity test which detects high amounts of acid in the stool as undigested lactose leads to lactic acid and other fatty acids.  The stool acidity test is intended for children, but because lactose intolerance is uncommon among children, doctors need consider other medical conditions in young children.

How is lactose intolerance managed?

One way to manage lactose intolerance is to avoid ingesting of milk and milk products.  Those who love milk or other dairy products may consider training their system to adapt to high doses of lactose. Start with small amounts and then gradually increase the amount of milk.   Of course those who don't like milk can simply avoid milk and other milk products to completely eliminate lactose intolerance.

Lactose intolerance and calcium intake

Milk and milk products are a major source of calcium, which is found high also in many vegetables or plant-based foods including white beans, tofu, Chinese cabbage, spinach and rhubarb. Those who have lactose intolerance may consider eating more plant-based foods that contain high amounts of calcium to make sure they have a high intake of the mineral.

What other products contain lactose?

Many foods may contain lactose.  The following list is not complete, but gives out the common ones:

bread and other baked goods

waffles, pancakes, biscuits, cookies, and mixes to make them

processed breakfast foods such as doughnuts, frozen waffles and pancakes, toaster pastries, and sweet rolls

processed breakfast cereals

instant potatoes, soups, and breakfast drinks

potato chips, corn chips, and other processed snacks

processed meats, such as bacon, sausage, hot dogs, and lunch meats

margarine

salad dressings

liquid and powdered milk-based meal replacements

protein powders and bars

candies

non-dairy liquid and powdered coffee creamers

non-dairy whipped toppings

Those who want to avoid lactose need to pay attention to keywords on the label including 

milk

lactose

whey

curds

milk by-products

dry milk solids

non-fat dry milk powder

Lactose may also be present in some prescription medicines, including birth control pills, and over-the-counter medicines like products to treat stomach acid and gas. These medicines most often cause symptoms in people with severe lactose intolerance, but may not cause any problem in those who have certain tolerance.

This article contain content from NIH Publication No. 09–2751 updated June 2009