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Lactose Intolerance

Many Americans suffer significant abdominal symptoms after ingesting significant quantities of milk and milk products.  While the fat content of such foods as milk, ice cream, and cheese can "set off" such conditions as gallbladder disease and gastrointestinal reflux, in many instances such bouts of abdominal symptoms after dairy product consumption is due to a condition called lactose intolerance.  Lactose intolerance is the inability to digest significant amounts of lactose, the predominant sugar of milk. This inability results from a shortage of the enzyme lactase, which is normally produced by the cells that line the small intestine.  Lactase breaks down milk sugar into simpler forms that can then be absorbed into the bloodstream. When there is not enough lactase to digest the amount of lactose consumed, the results, although not usually dangerous, may be very distressing. While not all persons deficient in lactase have symptoms, those who do are considered to be lactose intolerant.  Symptoms can include nausea, cramps, bloating, gas, and diarrhea, which begin about 30 minutes to 2 hours after eating or drinking foods containing lactose. The severity of symptoms varies depending on the different amount of lactose each individual with this condition can handle.  Lactose intolerance takes several forms. In a rare condition known as primary lactose intolerance, an infant does not produce any lactose from birth. These infants cannot tolerate breast milk and need to be under the care of a pediatrician and dietitian.  The more common type of lactose intolerance occurs after weaning and is known as secondary lactose intolerance. It is quite common.

Many people experience transient or episodic lactose intolerance related to well-known digestive conditions. For instance, certain disease processes and injuries to the small intestine can reduce the amount of enzymes produced.  Simple gastroenteritis ("stomach flu") can bring about a transient case of lactose intolerance.   In rare cases, children are born without the ability to produce lactase. For most people, though, lactase deficiency is a condition that develops naturally over time. After about the age of 2 years, the body begins to produce less lactase. However, many people may not experience symptoms until they are much older.

Between 30 and 50 million Americans are lactose intolerant. Certain ethnic and racial populations are more widely affected than others. As many as 75 percent of all African-Americans and Native Americans and 90 percent of Asian-Americans are lactose intolerant. The condition is least common among persons of northern European descent.

An accurate diagnosis is critical to make sure the symptoms you think are due to lactose intolerance are not a sign of some other medical problem.  One of the most common tests used to measure the absorption of lactose in the digestive system is the lactose tolerance test.  The lactose tolerance test begins with the individual fasting (not eating) before the test and then drinking a liquid that contains lactose. Several blood samples are taken over a 2-hour period to measure the person's blood glucose (blood sugar) level, which indicates how well the body is able to digest lactose.  Normally, when lactose reaches the digestive system, the lactase enzyme breaks down lactase 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  lactose is incompletely broken down the blood glucose level does not rise, and a diagnosis of lactose intolerance is suggested. The lactose tolerance test is not usually given to infants and very young children who are suspected of having lactose intolerance. Issues in pediatric patients should be promptly discussed with your child's pediatrician or other health care professional.

Fortunately, lactose intolerance is relatively easy to treat. No treatment exists to improve the body's ability to produce lactase, but symptoms can be controlled through diet.

For those who react to very small amounts of lactose or have trouble limiting their intake of foods that contain lactose, lactase enzymes are available without a prescription. One form is a liquid for use with milk. A few drops are added to a quart of milk, and after 24 hours in the refrigerator, the lactose content is reduced by 70 percent. The process works faster if the milk is heated first, and adding a double amount of lactase liquid produces milk that is 90 percent lactose free. A more recent development is a chewable lactase enzyme tablet that helps people digest solid foods that contain lactose. Three to six tablets are taken just before a meal or snack. Lactose-reduced milk and other products are available at many supermarkets. The milk contains all of the nutrients found in regular milk and remains fresh for about the same length of time or longer if it is super-pasteurized

.

Milk and other dairy products are a major source of nutrients in the American diet. The most important of these nutrients is calcium. Calcium is essential for the growth and repair of bones throughout life. In the middle and later years, a shortage of calcium may lead to thin, fragile bones that break easily (a condition called osteoporosis). A concern, then, for both children and adults with lactose intolerance, is getting enough calcium in a diet that includes little or no milk. 

In planning meals, making sure that each day's diet includes enough calcium is important, even if the diet does not contain dairy products. Many nondairy foods are high in calcium. Green vegetables, such as broccoli and kale, and fish with soft, edible bones, such as salmon and sardines, are excellent sources of calcium.  Recent research shows that yogurt with active cultures may be a good source of calcium for many people with lactose intolerance, even though it is fairly high in lactose. Evidence shows that the bacterial cultures used in making yogurt produce some of the lactase enzyme required for proper digestion.  Calcium is absorbed and used only when there is enough vitamin D in the body. A balanced diet should provide an adequate supply of vitamin D. Sources of vitamin D include eggs and liver. However, sunlight helps the body naturally absorb or synthesize vitamin D, and with enough exposure to the sun, food sources may not be necessary. Some people with lactose intolerance may think they are not getting enough calcium and vitamin D in their diet. Ask your doctor or other health care professional whether any dietary supplements are needed. Taking vitamins or minerals of the wrong kind or in the wrong amounts can be harmful.

 
Figure 2
 

People who are sensitive to lactose must also watch out for lactose contained in foods that would not normally seem to contain dairy components.  Although milk and foods made from milk are the only natural sources, lactose is often added to prepared foods. People with very low tolerance for lactose should know about the many food products that may contain lactose, even in small amounts. Food products that may contain lactose include the following:

  • 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.
Some products labeled nondairy, such as powdered coffee creamer and whipped toppings, may also include ingredients that are derived from milk and therefore contain lactose.  Smart shoppers learn to read food labels with care, looking not only for milk and lactose among the contents but also for such words as whey, curds, milk by-products, dry milk solids, and nonfat dry milk powder. If any of these are listed on a label, the item contains lactose.  In addition, lactose is used as the base for more than 20 percent of prescription drugs and about 6 percent of over-the-counter medicines. Many types of birth control pills, for example, contain lactose, as do some tablets for stomach acid and gas. However, these products typically affect only people with severe lactose intolerance.

Watching the foods you eat very closely can greatly decrease your symptoms if you are known to be lactose sensitive or intolerant. People who have trouble digesting lactose can learn which dairy products and other foods they can eat without discomfort and which ones they should avoid. Many will be able to enjoy milk, ice cream, and other such products if they take them in small amounts or eat other food at the same time. Others can use lactase liquid or tablets to help digest the lactose. Even older women at risk for osteoporosis and growing children who must avoid milk and foods made with milk can meet most of their special dietary needs by eating greens, fish, and other calcium-rich foods that are free of lactose. A carefully chosen diet (with calcium supplements if the doctor or dietitian recommends them) is the key to reducing symptoms and protecting future health.

(Adapted from NIDDK and other sources)