Lactose Intolerance
What is 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. See
figure 1. 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.
Common symptoms 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 amount of lactose each individual can
tolerate.
Some causes of lactose intolerance are well known. For instance, certain digestive diseases and injuries to the small intestine
can reduce the amount of enzymes produced. 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.
How Is Lactose Intolerance Diagnosed?
The most common tests used to measure the absorption of lactose in the digestive system are the lactose tolerance test, the
hydrogen breath test, and the stool acidity test. These tests are performed on an outpatient basis at a hospital, clinic,
or doctor's office.
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 confirmed.
The hydrogen breath test measures the amount of hydrogen in the breath. Normally, very little hydrogen is detectable in the
breath. However, undigested lactose in the colon is fermented by bacteria, and various gases, including hydrogen, are produced.
The hydrogen is absorbed from the intestines, carried through the bloodstream to the lungs, and exhaled. In the test, the
patient drinks a lactose-loaded beverage, and the breath is analyzed at regular intervals. Raised levels of hydrogen in the
breath indicate improper digestion of lactose. Certain foods, medications, and cigarettes can affect the test's accuracy and
should be avoided before taking the test. This test is available for children and adults.
The lactose tolerance and hydrogen breath tests are not given to infants and very young children who are suspected of having
lactose intolerance. A large lactose load may be dangerous for very young individuals because they are more prone to dehydration
that can result from diarrhea caused by the lactose. If a baby or young child is experiencing symptoms of lactose intolerance,
many pediatricians simply recommend changing from cow's milk to soy formula and waiting for symptoms to abate.
If necessary, a stool acidity test, which measures the amount of acid in the stool, may be given to infants and young children.
Undigested lactose fermented by bacteria in the colon creates lactic acid and other short-chain fatty acids that can be detected
in a stool sample. In addition, glucose may be present in the sample as a result of unabsorbed lactose in the colon.
How Is Lactose Intolerance Treated?
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.
Young children with lactase deficiency should not eat any foods containing lactose. Most older children and adults need not
avoid lactose completely, but individuals differ in the amounts of lactose they can handle. For example, one person may suffer
symptoms after drinking a small glass of milk, while another can drink one glass but not two. Others may be able to manage
ice cream and aged cheeses, such as cheddar and Swiss but not other dairy products. Dietary control of lactose intolerance
depends on each person's learning through trial and error how much lactose he or she can handle.
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.
How Is Nutrition Balanced?
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 1997, the Institute of Medicine released a report recommending new requirements for daily calcium intake. How much calcium
a person needs to maintain good health varies by age group. Recommendations from the report are as follows:
| Age group |
Amount of calcium to consume
daily in milligrams (mg)
|
| 0-6 months |
210 mg |
| 6-12 months |
270 mg |
| 1-3 years |
500 mg |
| 4-8 years |
800 mg |
| 9-18 years |
1,300 mg |
| 19-50 years |
1,000 mg |
| 51-70 years |
1,200 mg |
Also, pregnant and nursing women under 19 need 1,300 mg daily, while pregnant and nursing women over 19 need 1,000 mg.
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. To help in planning a high-calcium and low-lactose
diet, figure 2 lists some common foods that are good sources of dietary calcium and shows about how much lactose the foods
contain.
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.
Clearly, many foods can provide the calcium and other nutrients the body needs, even when intake of milk and dairy products
is limited. However, factors other than calcium and lactose content should be kept in mind when planning a diet. Some vegetables
that are high in calcium (Swiss chard, spinach, and rhubarb, for instance) are not listed in figure 2 because the body cannot
use their calcium content. They contain substances called oxalates, which stop calcium absorption. 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. Consultation
with a doctor or dietitian may be helpful in deciding whether any dietary supplements are needed. Taking vitamins or minerals
of the wrong kind or in the wrong amounts can be harmful. A dietitian can help in planning meals that will provide the most
nutrients with the least chance of causing discomfort.
What Is Hidden Lactose?
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:
- 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.
Summary
Even though lactose intolerance is widespread, it need not pose a serious threat to good health. 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.
National Digestive Diseases Information Clearinghouse
2 Information Way
Bethesda, MD 20892-3570
E-mail:
National Digestive Diseases Information Clearinghouse
The National Digestive Diseases Information Clearinghouse (NDDIC) is a service of the National Institute of Diabetes and Digestive
and Kidney Diseases (NIDDK). The NIDDK is part of the National Institutes of Health under the U.S. Department of Health and
Human Services. Established in 1980, the clearinghouse provides information about digestive diseases to people with digestive
disorders and to their families, health care professionals, and the public. NDDIC answers inquiries; develops, reviews, and
distributes publications; and works closely with professional and patient organizations and Government agencies to coordinate
resources about digestive diseases.
Publications produced by the clearinghouse are reviewed carefully for scientific accuracy, content, and readability.
This e-text is not copyrighted. The clearinghouse encourages users of this e-pub to duplicate and distribute as many copies
as desired.
NIH Publication No. 98-2751
April 1994
e-text updated: November 1998
