Lactose intolerance

Definition
Lactose intolerance is the inability to digest lactose, the predominant sugar in milk.

Understanding lactose
Lactose is found naturally in milk and foods made from milk, and it's often added to prepared foods. Lactose may also be found in nondairy products, such as creamers and whipped toppings. Other food products that may contain even small amounts of lactose include:
bread and bakery items
processed breakfast cereals
instant potatoes, soups and breakfast drinks
margarine
lunch meats (except the kosher variety)
salad dressings, gravies or sauce mixes
certain candies and other snacks
mixes for pancakes, biscuits and cookies
prepared products, such as frozen entrées
In addition to food products, lactose is used as the base for many prescription medications and a small number of over-the-counter medicines. Several types of birth control pills contain lactose. Lactose-based medications typically affect only those who have severe lactose intolerance.


Causes/associated factors
Lactose intolerance is related to a deficiency of the enzyme lactase, which is produced by the cells that line the small intestine. When lactose reaches the digestive system, the lactase enzyme breaks it down into simpler forms of sugar that can then be absorbed into the bloodstream.
About 50 million people in the United States have lactose intolerance. Up to 70 percent of African Americans, 90 percent of Asian Americans and 95 percent of Native Americans are lactose intolerant. Less than 25 percent of Caucasian adults have this condition.

Congenital lactose intolerance is common in infants who are premature, especially when delivery takes place before 30 weeks of pregnancy. In full-term infants, lactose intolerance is usually due to an inherited autosomal recessive trait that prevents lactase production. For adults, lactose intolerance often develops as a result of other gastrointestinal disorders -- such as Crohn's disease, celiac disease and Whipple's disease -- as well as gastrointestinal infections and injuries to the small intestine that interfere with the production of lactase.

Although the concentration of lactase levels at birth is high, the body begins to produce less lactase after about age 2. For most people, lactose intolerance develops over time, and symptoms don't appear until later in life (late onset). Not everyone who has a lactase deficiency will develop symptoms. Those who do are considered lactose intolerant.


Signs/symptoms
Symptoms usually begin about 15 minutes to three hours after eating foods containing lactose. Depending on how much lactose you can tolerate, symptoms may include:
nausea
cramping
bloating
gas
diarrhea
abdominal discomfort
for children, frothy, acidic stools
For adults, the symptoms of late-onset lactose intolerance are vague and may resemble various gastrointestinal disorders. If you suspect lactose intolerance, it's best to consult your doctor -- especially if your symptoms are severe or persistent.


Diagnosis
To base a diagnosis on your symptoms, the doctor will place you on a lactose-free diet for a specified period of time. If your symptoms disappear during this time, a lactase deficiency is likely. To confirm the diagnosis, specific tests or procedures may also be recommended.
Breath hydrogen test
For the breath hydrogen test, often recommended for older children and adults, you'll be given a drink containing 50 grams of lactose. Then, the amount of hydrogen in your breath will be measured. A rise in breath hydrogen of more than 20 parts per million (ppm) within 90 minutes is considered a positive test because it indicates bacterial carbohydrate metabolism. Certain foods and medications, as well as cigarettes, can affect test results. Follow your doctor's pretest instructions.

Lactose tolerance test
For this test, also recommended for older children and adults, you'll fast for a specified period of time and then drink a liquid that contains lactose. Several blood samples will be taken over a period of two hours to measure your blood glucose level, which indicates how well your body is able to digest lactose. If lactose is incompletely broken down, your blood glucose level will rise very little or not at all.

Stool acidity test
As the name implies, the stool acidity test measures the amount of acid in the stool. Undigested lactose is fermented by bacteria in the intestine, creating lactic acid and other short-chain fatty acids that are deposited in the stool.

Unlike the breath hydrogen and lactose intolerance tests, the stool acidity test may be given to infants and young children. Before giving the test, however, the doctor will often recommend changing from milk to a soy formula to see if symptoms clear up on their own.

Biopsy test
A biopsy of the small intestine (taking a tissue sample for further evaluation) can provide absolute confirmation of the diagnosis. The tissue sample is usually obtained through fiberoptic endoscopy, in which a tube is passed into the mouth, down the throat, and into the stomach and small intestine. In the lab, the tissue sample is measured for activity of the lactase enzyme.


Treatment
If you have trouble digesting lactose, you may be able to avoid symptoms by determining your lactose threshold. For example, most people can tolerate up to one to two glasses of milk per day without the use of lactase products. Plus, certain foods naturally contain lactase to aid in digestion. Unpasteurized yogurt contains bacteria that produce lactase, for example, and lactase-treated, 70 percent lactose-free milk is also available. To meet dietary requirements and prevent symptoms, spread your lactose servings throughout the day. Your doctor may also suggest lactase liquids or tablets to help you digest lactose.
At the supermarket, review labels not only for milk and lactose, but also for whey, milk byproducts, dry milk solids and nonfat dry milk powder. To meet your dietary needs for calcium, opt for calcium-rich foods other than dairy products. Consider the following lactose-free options from the American Dietetic Association and the U.S. Department of Agriculture:

sardines, 3 ounces -- calcium content: 371 milligrams
tofu processed with calcium salts, 3 ounces -- calcium content: 225 milligrams
canned salmon with bones, one serving -- calcium content: 167 milligrams
collard greens (cooked), 1 cup -- calcium content: 148 to 357 milligrams
kale (cooked), 1 cup -- calcium content: 94 to 179 milligrams
broccoli (cooked), 1 cup -- calcium content: 94 to 177 milligrams
calcium-fortified orange juice, 8 ounces -- calcium content: 300 to 350 milligrams
In comparison, 1 cup of milk (whole, skim or buttermilk) contains 291 to 316 milligrams of calcium and 12 to 13 grams of lactose. A cup of plain yogurt contains 274 to 415 milligrams of calcium and 12 to 13 grams of lactose. An ounce of processed cheese contains 159 to 219 milligrams of calcium and 2 to 3 grams of lactose.

Depending on your calcium consumption and overall health, your doctor may recommend calcium supplements. Remember, keeping your bones healthy is a lifelong process -- one that's never too late to start!


Complications
If you're lactose intolerant, a large amount of lactose can be dangerous because of the diarrhea it may cause. For infants and young children especially, diarrhea may lead to dehydration.
If you don't have enough calcium in your diet, either through food or supplements, you may face a calcium deficiency. This may increase your risk of osteoporosis, especially if you didn't build sufficient bone mass during early development. If this is a concern for you, consult your doctor or a registered dietitian about calcium supplementation.

Your intestinal lining may be damaged when a lactase deficiency is associated with certain other medical conditions (such as regional enteritis, cystic fibrosis, celiac disease, intestinal infection, ulcerative colitis, giardiasis or lipoprotein disorder).


Pregnancy-specific information
Nearly half of all pregnant women with a lactase deficiency can tolerate some lactose during pregnancy. Most pregnant women need to increase their calcium intake to meet the daily requirement of 1,000 milligrams. This is especially true for women under age 25 whose bones are still increasing in density. Calcium supplements will probably be recommended.

Senior-specific information
Growing older is not a risk factor for developing lactose intolerance.

Prevention
Although you can't prevent lactose intolerance, you can attempt to minimize its symptoms by following the suggestions in the treatment section above.