Lactose 

Intolerance 

National Digestive Diseases Information Clearinghouse 

U.S. Department 

of Health and 

Human Services 

NATIONAL 

INSTITUTES 

OF HEALTH 

What is lactose intolerance? 

Lactose intolerance is the inability or insufficient ability to digest lactose, a sugar found 

in milk and milk products. Lactose intolerance is caused by a deficiency of the enzyme 

lactase, which is produced by the cells lining 

the small intestine. Lactase breaks down 

lactose into two simpler forms of sugar 

called glucose and galactose, which are then 

absorbed into the bloodstream. 

Not all people with lactase deficiency have 

digestive symptoms, but those who do may 

have lactose intolerance. Most people 

with lactose intolerance can tolerate some 

amount of lactose in their diet. 

People sometimes confuse lactose intolerance with cow milk allergy. Milk allergy is a 

reaction by the body’s immune system to one 

or more milk proteins and can be life threatening when just a small amount of milk or 

milk product is consumed. Milk allergy most 

commonly appears in the first year of life, 

while lactose intolerance occurs more often 

in adulthood. 

What causes lactose 

intolerance? 

The cause of lactose intolerance is best 

explained by describing how a person develops lactase deficiency. 

Primary lactase deficiency develops over time 

and begins after about age 2 when the body 

begins to produce less lactase. Most children 

who have lactase deficiency do not experience symptoms of lactose intolerance until 

late adolescence or adulthood. 

Liver 

Appendix 

Large 

intestine 

The digestive tract. 

Stomach 

Anus 

Small 

intestine 

Researchers have identified a possible 

genetic link to primary lactase deficiency. 

Some people inherit a gene from their parents that makes it likely they will develop primary lactase deficiency. This discovery may 

be useful in developing future genetic tests to 

identify people at risk for lactose intolerance. 

Secondary lactase deficiency results from 

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 common in infancy. 
 

Who is at risk for lactose 

intolerance? 

Lactose intolerance is a common condition 

that is more likely to occur in adulthood, 

with a higher incidence in older adults. 

Some ethnic and racial populations are 

more affected than others, including African 

Americans, Hispanic Americans, American 

Indians, and Asian Americans. The condition is least common among Americans of 

northern European descent. 

Infants born prematurely are more likely to 

have lactase deficiency because an infant’s 

lactase levels do not increase until the third 

trimester of pregnancy. 

What are the symptoms of 

lactose intolerance? 

People with lactose intolerance may feel 

uncomfortable 30 minutes to 2 hours after 

consuming milk and milk products. Symptoms range from mild to severe, based on the 

amount of lactose consumed and the amount 

a person can tolerate. 

Common symptoms include 

•	 abdominal pain 

•	 abdominal bloating 

•	 gas 

•	 diarrhea 

•	 nausea 

How is lactose intolerance 

diagnosed? 

Lactose intolerance can be hard to diagnose 

based on symptoms alone. People may think 

they suffer from lactose intolerance because 

they have digestive symptoms; however, 

other conditions such as irritable bowel syndrome can cause similar symptoms. 

After taking a medical history and performing a physical examination, the doctor may 

first recommend eliminating all milk and 

milk products from the person’s diet for a 

short time to see if the symptoms resolve. 

Tests may be necessary to provide more 

information. 

Two tests are commonly used to measure the 

digestion of lactose. 

Hydrogen Breath Test. The person drinks a 

lactose-loaded beverage and then the breath 

is analyzed at regular intervals to measure 

the amount of hydrogen. Normally, very 

little hydrogen is detectable in the breath, 

but undigested lactose produces high levels 

of hydrogen. Smoking and some foods and 

medications may affect the accuracy of the 

results. People should check with their doctor about foods and medications that may 

interfere with test results. 

Stool Acidity Test. The stool acidity test is 

used for infants and young children to measure the amount of acid in the stool. Undigested lactose creates lactic acid and other 

fatty acids that can be detected in a stool 

sample. Glucose may also be present in the 

stool as a result of undigested lactose. 

Because lactose intolerance is uncommon 

in infants and children younger than 2, a 

health professional should take special care 

in determining the cause of a child’s digestive 

symptoms. 

2 Lactose Intolerance 
 

How is lactose intolerance 

managed? 

Although the body’s ability to produce 

lactase cannot be changed, the symptoms 

of lactose intolerance can be managed with 

dietary changes. Most people with lactose 

intolerance can tolerate some amount of 

lactose in their diet. Gradually introducing 

small amounts of milk or milk products may 

help some people adapt to them with fewer 

symptoms. Often, people can better tolerate 

milk or milk products by taking them with 

meals. 

The amount of change needed in the diet 

depends on how much lactose a person can 

consume without symptoms. For example, 

one person may have severe symptoms after 

drinking a small glass of milk, while another 

can drink a large glass without symptoms. 

Others can easily consume yogurt and hard 

cheeses such as cheddar and Swiss but not 

milk or other milk products. 

The Dietary Guidelines for Americans 2005 

recommend that people with lactose intolerance choose milk products with lower levels 

of lactose than regular milk, such as yogurt 

and hard cheese. 

Lactose-free and lactose-reduced milk and 

milk products, available at most supermarkets, are identical to regular milk except that 

the lactase enzyme has been added. Lactosefree milk remains fresh for about the same 

length of time or longer than regular milk 

if it is ultra-pasteurized. Lactose-free milk 

may have a slightly sweeter taste than regular 

milk. Soy milk and other products may be 

recommended by a health professional. 

People who still experience symptoms after 

dietary changes can take over-the-counter 

lactase enzyme drops or tablets. Taking the 

tablets or a few drops of the liquid enzyme 

when consuming milk or milk products may 

make these foods more tolerable for people 

with lactose intolerance. 

Parents and caregivers of a child with lactose intolerance should follow the nutrition 

plan recommended by the child’s doctor or 

dietitian. 

Lactose Intolerance and 

Calcium Intake 

Milk and milk products are a major source 

of calcium and other nutrients. Calcium is 

essential for the growth and repair of bones 

at all ages. A shortage of calcium intake in 

children and adults may lead to fragile bones 

that can easily fracture later in life, a condition called osteoporosis. 

The amount of calcium a person needs to 

maintain good health varies by age. Recommendations are shown in Table 1. 

Table 1. Recommended calcium intake by 

age group 

Amount of calcium 

to consume daily, 

Age group in milligrams (mg) 

0–6 months 210 mg 

7–12 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 

Source: Adapted from Dietary Reference Intakes, 2004, 


Institute of Medicine, National Academy of Sciences.
 

3 Lactose Intolerance 
 

 

Women who are pregnant or breastfeeding 

need between 1,000 and 1,300 mg of calcium 

daily. 

Getting enough calcium is important for 

people with lactose intolerance when the 

intake of milk and milk products is limited. 

Many foods can provide calcium and other 

nutrients the body needs. Non-milk products 

that are high in calcium include fish with soft 

bones such as salmon and sardines and dark 

green vegetables such as spinach. 

Table 2 lists foods that are good sources of 

dietary calcium. 

Table 2. Calcium content in common foods 

Non-milk Products Calcium Content 

Rhubarb, frozen, cooked, 1 cup 348 mg 

Sardines, with bone, 3 oz. 325 mg 

Spinach, frozen, cooked, 1 cup 291 mg 

Salmon, canned, with bone, 3 oz. 181 mg 

Soy milk, unfortified, 1 cup 61 mg 

Orange, 1 medium 52 mg 

Broccoli, raw, 1 cup 41 mg 

Pinto beans, cooked, 1/2 cup 40 mg 

Lettuce greens, 1 cup 20 mg 

Tuna, white, canned, 3 oz. 12 mg 

Milk and Milk Products 

Yogurt, with active and live cultures, plain, low-fat, 

vitamin D-fortified, 1 cup 415 mg 

Milk, reduced fat, vitamin D-fortified, 1 cup 285 mg 

Swiss cheese, 1 oz. 224 mg 

Cottage cheese, 1/2 cup 87 mg 

Ice cream, 1/2 cup 84 mg 

Source: Adapted from U.S. Department of Agriculture, Agricultural Research Service. 2008. USDA National 

Nutrient Database for Standard Reference, Release 21. 

4 Lactose Intolerance 

Yogurt made with active and live bacterial 

cultures is a good source of calcium for many 

people with lactose intolerance. When this 

type of yogurt enters the intestine, the bacterial cultures convert lactose to lactic acid, 

so the yogurt may be well-tolerated due to 

a lower lactose content than yogurt without 

live cultures. Frozen yogurt does not contain 

bacterial cultures, so it may not be welltolerated. 

Calcium is absorbed and used in the body 

only when enough vitamin D is present. 

Some people with lactose intolerance may 
 

not be getting enough vitamin D. Vitamin D 

comes from food sources such as eggs, liver, 

and vitamin D-fortified milk and yogurt. 

Regular exposure to sunlight also helps the 

body naturally absorb vitamin D. 

Talking with a doctor or registered dietitian may be helpful in planning a balanced 

diet that provides an adequate amount 

of nutrients—including calcium and 

vitamin D—and minimizes discomfort. A 

health professional can determine whether 

calcium and other dietary supplements are 

needed. 

What other products contain 

lactose? 

Milk and milk products are often added 

to processed foods—foods that have been 

altered to prolong their shelf life. People 

with lactose intolerance should be aware of 

the many food products that may contain 

even small amounts of lactose, such as 

•	 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 

Checking the ingredients on food labels is 

helpful in finding possible sources of lactose 

in food products. If any of the following 

words are listed on a food label, the product 

contains lactose: 

•	 milk 

•	 lactose 

•	 whey 

•	 curds 

•	 milk by-products 

•	 dry milk solids 

•	 non-fat dry milk powder 

Lactose is also used 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. 

5 Lactose Intolerance 
 

Points to Remember 

•	 Lactose intolerance is the inability or 

insufficient ability to digest lactose, a 

sugar found in milk and milk products. 

•	 Lactose intolerance is caused by a 

deficiency of the enzyme lactase, which 

is produced by the cells lining the small 

intestine. 

•	 Not all people with lactase deficiency 

have digestive symptoms, but those 

who do may have lactose intolerance. 

•	 Most people with lactose intolerance 

can tolerate some amount of lactose in 

their diet. 

•	 People with lactose intolerance may 

feel uncomfortable after consuming 

milk and milk products. Symptoms 

can include abdominal pain, abdominal bloating, gas, diarrhea, and nausea. 

•	 The symptoms of lactose intolerance 

can be managed with dietary changes. 

•	 Getting enough calcium and vitamin D 

is a concern for people with lactose 

intolerance when the intake of milk 

and milk products is limited. Many 

foods can provide the calcium and 

other nutrients the body needs. 

•	 Talking with a doctor or registered 

dietitian may be helpful in planning a 

balanced diet that provides an adequate amount of nutrients—including 

calcium and vitamin D—and minimizes discomfort. A health professional can determine whether calcium 

and other dietary supplements are 

needed. 

•	 Milk and milk products are often 


added to processed foods. Checking the ingredients on food labels is 


helpful in finding possible sources of 


lactose in food products. 


Hope through Research 

The National Institute of Diabetes and 

Digestive and Kidney Diseases’ (NIDDK’s) 

Division of Digestive Diseases and Nutrition conducts and supports basic and clinical 

research into digestive disorders. 

Participants in clinical trials can play a more 

active role in their own health care, gain 

access to new research treatments before 

they are widely available, and help others by 

contributing to medical research. For information about current studies, visit 

www.ClinicalTrials.gov. 

6	 Lactose Intolerance 
 

 

 

 

 

 

For More Information 

American Dietetic Association 

120 South Riverside Plaza, Suite 2000 

Chicago, IL 60606–6995 

Internet: www.eatright.org 

International Foundation for Functional 

Gastrointestinal Disorders 

P.O. Box 170864 

Milwaukee, WI 53217–8076 

Phone: 1–888–964–2001 or 414–964–1799 

Fax: 414–964–7176 

Email: iffgd@iffgd.org 

Internet: www.iffgd.org 

Acknowledgments 

Publications produced by the Clearinghouse 

are carefully reviewed by both NIDDK 

scientists and outside experts. This publication was originally reviewed by Eric Sibley, 

M.D., Ph.D., Stanford University School 

of Medicine. Rachel Fisher, M.S., M.P.H., 

R.D., and Jean Pennington, Ph.D., R.D., 

Division of Nutrition Research Coordination, NIDDK, reviewed the updated version 

of the publication. 

You may also find additional information about this 

topic by 

• searching the NIDDK Reference Collection at 

www.catalog.niddk.nih.gov/resources 

• visiting MedlinePlus at www.medlineplus.gov 

This publication may contain information about 

medications. When prepared, this publication 

included the most current information available. 

For updates or for questions about any medications, 

contact the U.S. Food and Drug Administration 

toll-free at 1–888–INFO–FDA (1–888–463–6332) or 

visit www.fda.gov. Consult your doctor for more 

information. 

7 Lactose Intolerance 
 

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The National Digestive Diseases Information 

Clearinghouse (NDDIC) is a service of the 

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and Kidney Diseases (NIDDK). The 

NIDDK is part of the National Institutes of 

Health of the U.S. Department of Health 

and Human Services. Established in 1980, 

the Clearinghouse provides information 

about digestive diseases to people with 

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The NDDIC answers inquiries, develops and 

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and Government agencies to coordinate 

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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. 09–2751 

June 2009