Def: A disorder characterized by abdominal cramps and diarrhea after consumption of food containing lactose (e.g., milk, ice cream); believed to reflect a deficiency of intestinal lactase; may appear first in young adults who had tolerated milk well as infants.
Alternative Names: Lactase deficiency; Milk intolerance; Disaccharidase deficiency; Dairy product intolerance
Lactose intolerance is the inability to digest a sugar called lactose that is found in milk and dairy products.
Normally when a person eats something containing lactose, an enzyme in the small intestine called lactase breaks down lactose into simpler sugar forms called glucose and galactose. These simple sugars are then easily absorbed into the bloodstream and turned into energy — fuel for our bodies.
People with lactose intolerance do not produce enough of the lactase enzyme to break down lactose. Instead, undigested lactose sits in the gut, causing gas, bloating, and stomach cramps. When the intestine cannot absorb the lactose-containing foods, it can lead to diarrhea.
Lactose intolerance is fairly common. It seems to affect guys and girls equally. Some ethnic groups are more likely to be affected than others because their diets traditionally include fewer dairy products: Almost all Asians and Native Americans are lactose intolerant, and up to 80% of African Americans and Hispanic Americans also have symptoms of lactose intolerance. Their ancestors did not eat dairy foods, so their bodies were not prepared to digest dairy, and they passed these genes on from generation to generation.
Little kids are less likely to have lactose intolerance. But many people eventually become lactose intolerant in adulthood — some while they are still teens. Some health care providers view lactose intolerance as a normal human condition and therefore don't really consider it a disease
Between 30 and 50 million Americans are lactose intolerant and certain ethnic and racial populations are more affected than others. Up to 80 percent of African Americans, 80 to 100 percent of American Indians, and 90 to 100 percent of Asian Americans are lactose intolerant. The condition is least common among people of northern European descent.
Babies that are born prematurely are also more likely to be lactose intolerant, because lactase levels do not increase until the third trimester of a woman's pregnancy.
Lactose intolerance is a very individual condition and it's often easy to manage if you're in tune with your body. Everyone's different, but most people with lactose intolerance are able to eat a small amount of dairy. The trick is to eat dairy products in combination with other foods that don't contain lactose and not eat too much dairy at once. It can also help to keep a food diary to learn which foods your body can or can't tolerate.
Dairy foods are the best source of calcium, a mineral that's important for bone growth. Because growing teens need about 1,300 milligrams (mg) of calcium each day, the American Academy of Pediatrics (AAP) recommends that even teens who have lactose intolerance continue to include some dairy in their diet.
Foods like cheese or yogurt may be easier to digest than milk, so try a cup of yogurt for dessert or add a piece of cheese to your sandwich. Lactose-free milk is also a great way to get calcium in your diet without the problems that can come with lactose.
Teens with the most severe symptoms of lactose intolerance may have to avoid all dairy products. It's extra important that these teens find other good calcium sources, so talking to a registered dietitian is a good idea. Dietitians are trained in nutrition and they can help people who are lactose intolerant come up with eating alternatives and develop a well-balanced diet that provides lots of calcium for developing strong bones.
Some tips for dealing with lactose intolerance:
Symptoms of lactose intolerance can be mild to severe, depending on how much lactase your body makes. Symptoms usually begin 30 minutes to 2 hours after you eat or drink milk products. If you have lactose intolerance, your symptoms may include:
- Choose lactose-reduced or lactose-free milk.
- Take a lactase enzyme supplement (such as Lactaid) just before you eat dairy products. These can be taken in drops or tablets and even added directly to milk.
- When you do drink milk or eat lactose-containing foods, eat other non-lactose foods at the same meal to slow digestion and avoid problems.
- Drink juices that are fortified with calcium.
- Eat a variety of dairy-free foods that are rich in calcium, such as broccoli, beans, tofu, or soy milk. Consider hard cheeses such as cheddar, which are lower in lactose.
- Yogurts that contain active cultures are easier to digest and much less likely to cause lactose problems.
Causes and Risk factors:
Lactose is a larger sugar that is made up of two smaller sugars, glucose and galactose. In order for lactose to be absorbed from the intestine and into the body, it must first be split into glucose and galactose. The glucose and galactose then are absorbed by the cells lining the small intestine. The enzyme that splits lactose into glucose and galactose is called lactase, and it is located on the surface of the cells that line the small intestine.
Lactose intolerance is caused by reduced or absent activity of lactase that prevents the splitting of lactose (lactase deficiency). Lactase deficiency may occur for one of three reasons, congenital, secondary or developmental.
Congenital causes of lactose intolerance: Lactase deficiency may occur because of a congenital absence of lactase due to a mutation in the gene that is responsible for producing lactase. This is a very rare cause of lactase deficiency, and the symptoms of this type of lactase deficiency begin shortly after birth.
Secondary causes of lactose intolerance: Another cause of lactase deficiency is secondary lactase deficiency. This type of deficiency is due to diseases that destroy the lining of the small intestine along with the lactase.
Developmental causes of lactose intolerance: The most common cause of lactase deficiency is a decrease in the amount of lactase that occurs after childhood and persists into adulthood, referred to as adult-type hypolactasia. This decrease is genetically programmed, and the prevalence of this type of lactase deficiency among different ethnic groups is highly variable. Thus, among Asian populations it is almost 100%, among American Indians it is 80%, and among blacks it is 70%; however, among American Caucasians the prevalence of lactase deficiency is only 20%. In addition to variability in the prevalence of lactase deficiency, there also is variability in the age at which symptoms of lactose intolerance appear. Thus, among Asian populations, the symptoms of deficiency (intolerance) occur around the age of 5, among Blacks and Mexican-Americans by the age of 10, and among the Finnish by age 20.
It is important to emphasize that lactase deficiency is not the same as lactose intolerance. Persons with milder deficiencies of lactase often have no symptoms after the ingestion of milk. For unclear reasons, even persons with moderate deficiencies of lactase may not have symptoms. A diagnosis of lactase deficiency is made when the amount of lactase in the intestine is reduced, but a diagnosis of lactose intolerance is made only when the reduced amount of lactase causes symptoms.
Race: Persons of all races are affected by lactose intolerance, with higher prevalence among Asian, African, and South American persons.
- Pain or cramps.
- Gurgling or rumbling sounds in your belly.
- Loose stools or diarrhea.
- Throwing up.
Age: Among adults, the age of presentation of lactose intolerance is 20-40 years.
Lactose intolerance can be hard to diagnose based on symptoms alone. People sometimes think they suffer from lactose intolerance because they have the symptoms associated with the disorder, not knowing other conditions such as irritable bowel syndrome can cause similar symptoms. A doctor can use tests to diagnose lactose intolerance but may first recommend eliminating cow's milk from the diet to see if the symptoms go away.
The most common tests used to measure the absorption of lactose in the digestive system are the lactose tolerance, hydrogen breath, and stool acidity tests.
The Lactose Tolerance Test: This test requires fasting (not eating) before the test and then drinking a liquid that contains lactose. Several blood samples are then taken over a 2-hour period to measure the person's blood glucose (blood sugar) level. These measures indicate how well the body is able to digest lactose.
Normally, when lactose reaches the digestive system, the lactase enzyme breaks it down 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, however, lactose is incompletely broken down, the blood glucose level does not rise and a diagnosis of lactose intolerance is confirmed.
The Hydrogen Breath Test: This test measures the amount of hydrogen in a person's breath. Very little hydrogen is normally detectable. However, undigested lactose in the colon is fermented by bacteria and produces various gases, including hydrogen. The hydrogen is absorbed from the intestines, carried through the bloodstream to the lungs, and exhaled. In this test, the person 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 accuracy of the test and should be avoided before taking the test. People should check with their doctor to make sure they are not taking medications that may interfere with test results. The lactose tolerance and hydrogen breath tests are not given to infants younger than 6 months of age. A large lactose load can be dangerous prior to this age, as infants are more likely to become dehydrated from diarrhea that can be caused by lactose intolerance.
Stool Acidity Test. This test may be used for infants and young children to measure the amount of acid in their stool. Undigested lactose fermented by bacteria in the colon creates lactic acid and other fatty acids that can be detected in a stool sample. Glucose may also be present in the sample as a result of unabsorbed lactose in the colon.
It is now possible to test the DNA of individuals to make a diagnosis of lactose intolerance. This is likely to be an important research tool for studying lactase deficiency and lactose intolerance. It is still too early to know how helpful this sophisticated testing will be in the clinical evaluation and treatment of patients. It is an expensive test.
In 1998, scientists were able to make lactose intolerant rats tolerant of lactose by transferring the gene for lactase to their intestinal lining cells. It is unlikely that this type of gene therapy will find much of an application in people. Nevertheless, it is a fascinating example of what science can accomplish.
- Males and females are equally affected by lactose intolerance.
- Of those women who are lactose intolerant, 44% regain the ability to digest lactose during pregnancy. This is probably due to slow intestinal transit and bacterial adaptation during pregnancy.
Lactose intolerance is easy to treat. No treatment can improve the body's ability to produce lactase, but symptoms can be controlled through diet.
Young children and infants with lactase deficiency should not consume lactose-containing formulas or foods until they are able to tolerate lactose digestion. Most older children and adults do not have to avoid lactose completely, but people differ in the amounts and types of foods they can handle. For example, one person may have 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. People can also tolerate more lactose by having smaller amounts of it at one time. The level of dietary control needed with lactose intolerance depends on how much lactose a person's body can handle.
For those who react to very small amounts of lactose or have trouble limiting their intake of foods that contain it, the lactase enzyme is available without a prescription to help people digest foods that contain lactose. The tablets are taken with the first bite of dairy food. Lactase enzyme is also available as a liquid. Adding a few drops of the enzyme makes lactose more digestible for people with lactose intolerance.
Lactose-reduced milk and other products are available at most 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.
In planning meals, people with lactose intolerance should make sure that each day's diet includes enough calcium, even if dairy products are not included. Many non-dairy foods are high in calcium, including dark green vegetables such as broccoli, or fish with soft, edible bones, such as salmon and sardines. To help in planning a high-calcium, low-lactose diet, the table that follows lists some common foods that are good sources of dietary calcium and shows how much lactose they contain.
Recent research shows that yogurt with active cultures may be a good source of calcium for many people with lactose 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.
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 example) are not listed in the chart because the body cannot use the calcium they contain because these foods also 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 from sources such as eggs and liver. Sunlight also helps the body naturally absorb 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 dietary supplements are needed. Taking vitamins or minerals of the wrong kind or in the wrong amounts can be harmful. A dietitian can help plan meals that will provide the most nutrients with the least chance of causing discomfort.
Medicine and medications:
Lactase enzymes (LACTAID, Dairy Ease, Lactrase): For patients with lactase enzymatic deficiency. Prevent osmotic diarrhea in patients deficient in lactase enzymes who consume milk.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.