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Lactose
Intolerance
National Digestive Diseases Information Clearinghouse
What is lactose intolerance? What are the symptoms of
Lactose intolerance is the inability to digest lactose intolerance?
significant amounts of lactose, the major People who do not have enough lactase to
National sugar found in milk. Lactose intolerance is digest the amount of lactose they consume
Institute of
Diabetes and caused by a shortage of the enzyme lactase, may feel very uncomfortable when they
Digestive which is produced by the cells that line the digest milk products. Common symptoms,
and Kidney
Diseases
small intestine. Lactase breaks down milk which range from mild to severe, include
NATIONAL sugar into two simpler forms of sugar called nausea, cramps, bloating, gas, and diarrhea.
INSTITUTES glucose and galactose, which are then
OF HEALTH Symptoms begin about 30 minutes to 2
absorbed into the bloodstream. Not all hours after eating or drinking foods con
people deficient in lactase have the symp taining lactose. The severity of symptoms
toms commonly associated with lactose depends on many factors, including the
intolerance, but those who do are said to amount of lactose a person can tolerate and
have lactose intolerance. a person’s age, ethnicity, and digestion rate.
People sometimes confuse lactose intoler
ance with cow’s milk intolerance because
the symptoms are often the same. How
ever, lactose intolerance and cow’s milk
intolerance are not related. Being intoler
ant to cow’s milk is an allergic reaction
triggered by the immune system. Lactose
intolerance is a problem caused by the
digestive system.
Stomach
Small
intestine
Colon
Rectum
The digestive tract
U.S. Department
of Health and
Human Services
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How is lactose intolerance • The Hydrogen Breath Test. This test
measures the amount of hydrogen in a
diagnosed? person’s breath. Very little hydrogen
Lactose intolerance can be hard to diag is normally detectable. However,
nose based on symptoms alone. People undigested lactose in the colon is
sometimes think they suffer from lactose fermented by bacteria and produces
intolerance because they have the symp various gases, including hydrogen.
toms associated with the disorder, not The hydrogen is absorbed from the
knowing other conditions such as irritable intestines, carried through the blood
bowel syndrome can cause similar symp stream to the lungs, and exhaled. In
toms. A doctor can use tests to diagnose this test, the person drinks a lactose-
lactose intolerance but may first recom loaded beverage and the breath is
mend eliminating cow’s milk from the diet analyzed at regular intervals. Raised
to see if the symptoms go away. levels of hydrogen in the breath indi
cate improper digestion of lactose.
The most common tests used to measure
Certain foods, medications, and
the absorption of lactose in the digestive
cigarettes can affect the accuracy of
system are the lactose tolerance, hydrogen
the test and should be avoided before
breath, and stool acidity tests.
taking the test. People should check
• The Lactose Tolerance Test. This test with their doctor to make sure they
requires fasting (not eating) before are not taking medications that may
the test and then drinking a liquid interfere with test results.
that contains lactose. Several blood
samples are then taken over a 2-hour The lactose tolerance and hydrogen breath
period to measure the person’s blood tests are not given to infants younger than
glucose (blood sugar) level. These 6 months of age. A large lactose load can
measures indicate how well the body be dangerous prior to this age, as infants
is able to digest lactose. are more likely to become dehydrated from
diarrhea that can be caused by lactose
Normally, when lactose reaches the intolerance.
digestive system, the lactase enzyme
• Stool Acidity Test. This test may be
breaks it down into glucose and
used for infants and young children to
galactose. The liver then changes the
measure the amount of acid in their
galactose into glucose, which enters
stool. Undigested lactose fermented
the bloodstream and raises the per
by bacteria in the colon creates lactic
son’s blood glucose level. If, however,
acid and other fatty acids that can be
lactose is incompletely broken down,
detected in a stool sample. Glucose
the blood glucose level does not rise
may also be present in the sample as
and a diagnosis of lactose intolerance
a result of unabsorbed lactose in the
is confirmed.
colon.
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What causes lactose How is lactose intolerance
intolerance? treated?
Some causes of lactose intolerance are well Lactose intolerance is easy to treat. No
known. Primary lactase deficiency is a con treatment can improve the body’s ability
dition that develops over time. After about to produce lactase, but symptoms can be
age 2 the body begins to produce less lac controlled through diet.
tase, though most people will not notice
Young children and infants with lactase
symptoms until they are much older.
deficiency should not consume lactose-
Secondary lactase deficiency occurs when containing formulas or foods until they are
injury to the small intestine or certain able to tolerate lactose digestion. Most
digestive diseases reduce the amount of older children and adults do not have to
lactase a person produces. These diseases avoid lactose completely, but people differ
include celiac disease, inflammatory bowel in the amounts and types of foods they can
disease, and Crohn’s disease. handle. For example, one person may have
symptoms after drinking a small glass of
Researchers have identified a genetic link
milk, while another can drink one glass but
for lactose intolerance. Some people are
not two. Others may be able to manage ice
born with a likelihood of developing pri
cream and aged cheeses, such as cheddar
mary lactase deficiency because it has been
and Swiss, but not other dairy products.
passed to them genetically (inherited from
People can also tolerate more lactose by
their parents). This discovery may be
having smaller amounts of it at one time.
useful in developing a diagnostic test to
The level of dietary control needed with
identify people with the condition.
lactose intolerance depends on how much
lactose a person’s body can handle.
Who is at risk for lactose For those who react to very small amounts
intolerance? of lactose or have trouble limiting their
Between 30 and 50 million Americans are intake of foods that contain it, the lactase
lactose intolerant and certain ethnic and enzyme is available without a prescription
racial populations are more affected than to help people digest foods that contain
others. Up to 80 percent of African lactose. The tablets are taken with the first
Americans, 80 to 100 percent of American bite of dairy food. Lactase enzyme is also
Indians, and 90 to 100 percent of Asian available as a liquid. Adding a few drops of
Americans are lactose intolerant. The the enzyme makes lactose more digestible
condition is least common among people for people with lactose intolerance.
of northern European descent.
Lactose-reduced milk and other products
Babies that are born prematurely are are available at most supermarkets. The
also more likely to be lactose intolerant, milk contains all of the nutrients found in
because lactase levels do not increase until regular milk and remains fresh for about
the third trimester of a woman’s pregnancy. the same length of time, or longer if it is
super-pasteurized.
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How is nutrition balanced? In addition, pregnant and nursing women
need between 1,200 and 1,500 mg of calci
Milk and other dairy products are a major um daily.
source of nutrients in the American diet.
One of the most important of these nutri In planning meals, people with lactose
ents is calcium. Calcium is essential for the intolerance should make sure that each
growth and repair of bones throughout life. day’s diet includes enough calcium, even
In the middle and later years, a shortage of if dairy products are not included. Many
calcium may lead to thin, fragile bones that non-dairy foods are high in calcium, includ
break easily, a condition called osteoporo ing dark green vegetables such as broccoli,
sis. A concern for both children and adults or fish with soft, edible bones, such as
with lactose intolerance is getting enough salmon and sardines. To help in planning
calcium in a diet that includes little or no a high-calcium, low-lactose diet, the table
dairy products. that follows lists some common foods that
are good sources of dietary calcium and
The Institute of Medicine released a report shows how much lactose they contain.
listing the requirements for daily calcium
intake. How much calcium a person needs Recent research shows that yogurt with
to maintain good health varies by age active cultures may be a good source of
group. Recommendations from the report calcium for many people with lactose
are shown in the following table. intolerance. Even though yogurt is fairly
high in lactose, the bacterial cultures used
to make it produce some of the lactase
enzyme required for proper digestion.
Amount of calcium
to consume daily, Clearly, many foods can provide the calci
Age group in milligrams (mg) um and other nutrients the body needs,
0–6 months 400 mg even when intake of milk and dairy prod
ucts is limited. However, factors other
6–12 months 600 mg than calcium and lactose content should be
1–5 years 800 mg kept in mind when planning a diet. Some
6–10 years 1,200 mg vegetables that are high in calcium (Swiss
chard, spinach, and rhubarb, for example)
11–24 years 1,200–1,500 mg are not listed in the chart because the
19–50 years 1,000 mg body cannot use the calcium they contain
51–70+ years 1,500 mg because these foods also contain substances
called oxalates, which stop calcium
absorption.
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Calcium and Lactose in Common Foods
Nondairy Products Calcium Content Lactose Content
Soymilk, fortified, 1 cup 200–300 mg 0
Sardines, with edible bones, 3 oz. 270 mg 0
Salmon, canned, with edible bones, 3 oz. 205 mg 0
Broccoli, raw, 1 cup 90 mg 0
Orange, 1 medium 50 mg 0
Pinto beans, 1/2 cup 40 mg 0
Tuna, canned, 3 oz. 10 mg 0
Lettuce greens, 1/2 cup 10 mg 0
Dairy Products
Yogurt, plain, low-fat, 1 cup 415 mg 5g
Milk, reduced fat, 1 cup 295 mg 11 g
Swiss cheese, 1 oz. 270 mg 1g
Ice cream, 1/2 cup 85 mg 6g
Cottage cheese, 1/2 cup 75 mg 2–3 g
Adapted from Manual of Clinical Dietetics. 6th ed. American Dietetic Association, 2000; and Soy
Dairy Alternatives. Available at: www.soyfoods.org.
Calcium is absorbed and used only when Some people with lactose intolerance may
there is enough vitamin D in the body. A think they are not getting enough calcium
balanced diet should provide an adequate and vitamin D in their diet. Consultation
supply of vitamin D from sources such as with a doctor or dietitian may be helpful in
eggs and liver. Sunlight also helps the deciding whether dietary supplements are
body naturally absorb vitamin D, and with needed. Taking vitamins or minerals of the
enough exposure to the sun, food sources wrong kind or in the wrong amounts can be
may not be necessary. harmful. A dietitian can help plan meals
that will provide the most nutrients with the
least chance of causing discomfort.
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What is hidden lactose? Lactose is also used in more than 20
percent of prescription drugs and about
Although milk and foods made from milk 6 percent of over-the-counter medicines.
are the only natural sources of lactose, it is Many types of birth control pills contain
often added to prepared foods. People lactose, as do some tablets for stomach acid
with very low tolerance for lactose should and gas. However, these products typically
know about the many food products that affect only people with severe lactose
may contain even small amounts of lactose, intolerance.
such as
• bread and other baked goods Summary
• processed breakfast cereals Even though lactose intolerance is com
mon, it is not a threat to good health.
• instant potatoes, soups, and People who have trouble digesting lactose
breakfast drinks can learn which dairy products and other
foods they can eat without discomfort and
• margarine
which ones they should avoid. Many peo
• lunch meats (other than kosher) ple can enjoy milk, ice cream, and other
such products if they eat them in small
• salad dressings amounts or eat other food at the same
time. Others can use lactase liquid or
• candies and other snacks tablets to help digest the lactose. Even
• mixes for pancakes, biscuits, and older women at risk for osteoporosis and
cookies growing children who must avoid milk and
foods made with milk can meet most of
• powdered meal-replacement their dietary needs by eating greens, fish,
supplements and other calcium-rich foods that are free
of lactose. A carefully chosen diet, with
Some products labeled non-dairy, such as calcium supplements if the doctor or
powdered coffee creamer and whipped dietitian recommends them, is the key
toppings, may actually include ingredients to reducing symptoms.
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.
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For More Information
American Dietetic Association (ADA)
120 South Riverside Plaza
Suite 2000
Chicago, IL 60606–6995
Phone: 1–800–877–1600
Fax: 312–899–4899
Internet: www.eatright.org
International Foundation for Functional
Gastrointestinal Disorders (IFFGD) Inc.
P.O. Box 170864
Milwaukee, WI 53217
Phone: 1–888–964–2001 or 414–964–1799
Fax: 414–964–7176
Email: iffgd@iffgd.org
Internet: www.iffgd.org
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National Digestive Diseases
Information Clearinghouse
2 Information Way
Bethesda, MD 20892–3570
Phone: 1–800–891–5389
Fax: 703–738–4929
Email: nddic@info.niddk.nih.gov
Internet: www.digestive.niddk.nih.gov
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 Clearing-
house provides information about digestive
diseases to people with digestive disorders and
to their families, health care professionals, and
the public. The NDDIC answers inquiries,
develops 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
carefully reviewed by both NIDDK scientists
and outside experts. This fact sheet was
reviewed by Eric Sibley, M.D., Ph.D.,
Stanford University School of Medicine.
This publication is not copyrighted. The
Clearinghouse encourages users of this fact
sheet to duplicate and distribute as many
copies as desired.
This fact sheet is also available at
www.digestive.niddk.nih.gov.
U.S. DEPARTMENT OF HEALTH
AND HUMAN SERVICES
National Institutes of Health
NIH Publication No. 06–2751
March 2006
