Milk Intolerance – Causes, Signs and symptoms

Milk Intolerance

Also called: Lactose Intolerance


Milk intolerance is an inability to break down the main sugar found in dairy products (lactose) due to the lack of a specific digestive enzyme (lactase). This results in symptoms such as gas, bloating and abdominal pain. Milk intolerance is not the same as a milk allergy, because the immune system is not involved in the reaction.

Milk intolerance is a common condition. According to the National Digestive Diseases Information Clearinghouse, between 30 million and 50 million Americans are intolerant to lactose to some degree. Almost 75 percent of all African Americans and 90 percent of Asian Americans are intolerant to lactose.

Milk intolerance can be the result of the body gradually creating less and less lactase over time, or it can come as the result of sudden damage to the small intestine (e.g., viral infection, stomach flu, surgery). Milk intolerance is a condition that is often genetically passed on from parent to child. In some rare cases a child is born without the ability to produce lactase at all.

The most effective treatment for milk intolerance is to limit or completely remove lactose from the diet. Milk intolerance symptoms and reactions vary between individuals, and some people will be affected by some dairy products that other individuals can tolerate without symptoms. Patients experiencing the symptoms of milk intolerance should discuss the problem with their physician to rule out conditions with similar symptoms (e.g., irritable bowel syndrome).

Adjusting the diet to accommodate milk intolerance may mean choosing other foods or taking dietary supplements in order to get healthy amounts of some dietary nutrients – primarily calcium. A physician can provide this type of dietary guidance or recommend a dietician who can help.

Individuals with milk intolerance can sometimes use supplements of lactase in order to tolerate small amounts of foods that contain lactose. Also, some dairy products come in “lactose free” versions that can be safely enjoyed by someone with milk intolerance without the risk of symptoms occurring.

About milk intolerance

Milk intolerance (lactose intolerance) occurs when the body is unable to produce enough of the enzyme lactase, which is needed to break down lactose for easy digestion. It is important to note that milk intolerance is not the same as a milk allergy, because milk intolerance does not involve the immune system, which is a key player in all types of allergic reactions.

Lactose is a naturally occurring sugar found in milk and dairy products. The lactase enzyme, which is produced by the cells that line the small intestine, breaks lactose down into the sugars glucose and galactose. This reaction occurs in the small intestine as a normal part of digestion. Once lactose has been properly broken down by the lactase, it can be easily absorbed into the bloodstream.

Some individuals are lactase deficient, meaning their small intestines do not produce enough lactase to break down all the lactose. This deficiency could be the result of damage sustained to the lower intestine or due to an inherited intolerant condition. In many cases, a lactase-deficient person may not experience symptoms. However, those individuals who do experience symptoms are considered lactose intolerant.  

If lactose is not properly broken down and digested, water remains in the bowel. This can result in bloating and watery diarrhea. The lactose that passes on into the large intestine comes into contact with naturally occurring bacteria, which ferments the lactose. The result is the production of carbon dioxide, hydrogen and methane. This excess gas leads to additional bloating, cramping and flatulence (passing gas). The hydrogen gas often travels through the bloodstream to the lungs, where it can cause bad breath.

The ability of a person to break down lactose and tolerate dairy products varies greatly by individual. For example, a person who has sustained severe damage to the lower intestine may be unable to tolerate any food containing lactose.

Different types of dairy (e.g., milk, cheese) contain different amounts of lactose. For this reason, some people with milk intolerance can eat some types of dairy without symptoms, while other individuals with milk intolerance must avoid dairy entirely.

According to the National Digestive Diseases Information Clearinghouse, between 30 million and 50 million Americans are intolerant to lactose to some degree. Almost 75 percent of all African Americans and 90 percent of Asian Americans are intolerant to lactose.

Milk intolerance can begin at various ages. In Caucasians, the condition usually begins to affect children over the age of 5. In African Americans, the condition can occur in children as young as 2.  

Types and causes of milk intolerance

The types of milk intolerance are distinguished mainly by their cause and at what point in the patient’s life they develop. All of these types of milk intolerance share the same symptoms and are treated in a similar manner. The types of milk intolerance include:

  • Adult lactose intolerance. Symptoms usually begin in the teen years. This is the most common type of milk intolerance and is often an inherited condition. A small amount of milk may be tolerated each day (about 8 ounces on average), depending on an individual’s production of lactase. The severity of this type of intolerance usually persists or slightly worsens as the individual grows older.

  • Acquired lactose intolerance (secondary lactose intolerance). Occurs when the small intestine partially or completely discontinues the production of the enzyme lactase. This condition often comes as a result of an illness (e.g., viral stomach flu) or another medical condition (e.g. cystic fibrosis, celiac disease). This type of milk intolerance can occur at any age. Whether this condition is temporary or permanent depends on the amount of damage to the intestine and, therefore, the amount of lactase the body is able to produce.

  • Congenital lactose intolerance. Rare but permanent condition in which children are born without the ability to produce lactase. Patients with this type of milk intolerance must avoid foods or drinks with lactose for their entire lives. 

Some factors increase the risk of an individual developing milk intolerance. These include:

  • Family history. Milk intolerance has been linked to a specific genetic variation, and parents with an intolerance are more likely to pass this condition on to their children.

  • Ethnicity. Certain ethnic and racial groups suffer from milk intolerance more than others. For instance, African Americans, Asian Americans and Native Americans are much more likely to have this condition than are individuals of northern European descent. Hispanics and those of Ashkenazi Jewish descent are also at increased risk.

  • Premature birth. Because the lactase enzyme increases in the fetus during the third trimester, there is increased likelihood of infants developing milk intolerance if they are born at 28 to 32 weeks of gestation.

  • Certain medications. People taking certain antibiotics risk developing temporary milk intolerance. This occurs when the medication interferes with the body’s ability to produce lactase.

  • Age. Most people become lactose intolerant over time. This occurs as the body ages and stops producing lactase. 

Signs and symptoms of milk intolerance

Symptoms of milk intolerance can be very uncomfortable. Individuals who experience these symptoms should contact their physician to rule out any other medical conditions with similar symptoms (e.g., irritable bowel syndrome).

Symptoms usually begin between 30 minutes and two hours after consuming a food or drink that contains lactose. The severity of the symptoms varies depending on the amount of lactose consumed and the sensitivity of the individual. Common symptoms include:

  • Diarrhea
  • Gas
  • Stomach cramps
  • Nausea
  • Abdominal bloating or distension (expansion from inner pressure)
  • Bad breath

Individuals who have removed milk and other dairy products from their diet often suffer from some form of calcium and vitamin D deficiency. A lack of sufficient calcium increases the risk of developing osteoporosis, which can lead to bone fractures. A lack of vitamin D can cause bone disease and bone fractures. Both calcium and vitamin D can be added to the diet through other types of foods or dietary supplements.

Diagnosis methods for milk intolerance

There are several tests and procedures for clinically diagnosing milk intolerance. These tests and procedures can all be performed at a physician’s office or a hospital on an outpatient basis. The need for these tests often depends on the severity of the condition. Or, the physician may need to exclude a more serious type of condition that shares similar symptoms (e.g., viral flu).

Many people who self-diagnose milk intolerance end up making the wrong diagnosis. Individuals who suspect milk intolerance should not underestimate the value of visiting a physician and receiving formal testing. The tests and procedures most often used include:

  • Elimination diet. Involves the removal of foods that contain lactose from a patient’s diet to see if milk intolerance symptoms persist. This should be done under the guidance of a physician or a registered dietitian. People who attempt to self-diagnose milk intolerance often overlook foods that contain milk and fail to remove them from their diet. Many people also conduct the diet for an inadequate period of time to gather conclusive results.
  • Lactose intolerance test. Measures blood glucose (blood sugar) levels for signs that indicate milk intolerance. To begin the test, the patient is given a lactose-loaded drink. Several blood samples are then taken from the patient over the next two hours. The amount of glucose found in the blood samples indicates how well the patient’s body is able to digest lactose. The patient will be required to not eat before the test. This type of test is not normally given to infants and young children because of safety concerns involving a high-lactose drink.
  • Hydrogen breath test. Measures whether there is an abnormal amount of hydrogen in the breath. Normally hydrogen cannot be detected in the breath. However, people with milk intolerance may have it in their breath after ingesting lactose. Undigested lactose in the colon ferments as a result of the bacteria present there, producing several gases, including hydrogen. The hydrogen is absorbed from the intestines into the bloodstream, where it travels to the lungs.

    The test results can be affected by certain foods, medications or cigarettes. The consumption of a high-lactose drink makes this test unsafe for young children or infants, but can be safely used on older children.
  • Stool acidity test. Measures the amount of acid present in the stool. Lactic acid and other fatty acids are created when undigested lactose ferments in the colon. These then pass into the stool. The test may also look for glucose, which indicates the presence of unabsorbed lactose in the colon. This type of test is safe to perform on patients of all ages, including infants and young children.
  • Milk challenge. Simple method often used to self-diagnose milk intolerance. The challenge consists of a period of fasting (usually overnight) followed by the consumption of a single glass of milk. No other types of food or drink are consumed for the next three to five hours. If a person has a milk intolerance, symptoms should appear within several hours.

Treatment and prevention of milk intolerance

Milk intolerance is relatively easy to treat. Although treatment cannot improve the body’s ability to produce lactase, patients can effectively control their symptoms through diet.

Treating milk intolerance depends on the condition and the symptoms. Some people may be able to tolerate small amounts of milk or dairy in a different form, such as cheese. If symptoms are severe, then complete avoidance may be necessary.

Milk-intolerant people must educate themselves about foods containing hidden sources of lactose. Most types of dairy are obvious, but a person must still read the ingredient label carefully on all foods to make sure milk or lactose is not present. Unexpected products that contain lactose include:

  • Cereal
  • Breads
  • Lunch meats
  • Instant soups, potatoes and breakfast drinks
  • Salad dressings
  • Milk chocolate
  • Margarine
  • Baking mixes
  • Frozen dinners
  • Candy
  • Medicines (e.g., birth control pills)

Patients should also check the ingredient labels for any of the following terms that indicate the presence of lactose:

  • Whey
  • Milk byproducts
  • Nonfat dry milk powder
  • Malted milk
  • Buttermilk
  • Dry milk solids
  • Curds

Many people suffer from milk intolerance conditions that do not require them to completely avoid lactose. How much lactose a person can tolerate varies by individual, as does sensitivity to particular foods. For instance, some people can tolerate up to 8 ounces of milk a day with few symptoms. Young children and infants with a lactase deficiency should avoid all foods containing lactose until they are older. Lactose-free infant formulas are available for infants who are lactose intolerant.

Trial and error is frequently the only way to figure out which foods will cause symptoms and which can be tolerated. For example, some people can eat ice cream and some cheeses, but must avoid other types of cheeses and all other forms of dairy. Other people can only tolerate an occasional small glass of milk. Individuals with mild milk intolerance can often tolerate Swiss cheese, cheddar cheese and yogurt.

Lactase supplements can be taken with a dairy food to aid in digestion. These over-the-counter products contain the enzyme lactase and are available in both tablets and liquid forms. They should be taken just before or with consumption of the food containing lactose. For instance, the liquid form can be mixed with a glass of milk.

Lactase supplements are effective, but they are not a cure. The supplements take up to 24 hours to completely break down the lactose in a food, which means they cannot effectively handle large amounts of lactose.

Some types of dairy come in lactose-free forms. These products are often available at specialty grocery stores. An individual should always be sure that a product’s package is clearly marked as lactose-free before consuming it. Patients who are unsure about a food can contact the product’s manufacturer.

Individuals who find it difficult to avoid lactose in their diets should consult a physician, who will often recommend dietary counseling. This will allow patients to plan their diet with expert advice.

Management tips for milk intolerance

It is important for individuals who are avoiding or limiting the consumption of dairy products to supplement their diets with many of the essential nutrients they may be missing as a result (e.g., vitamin A, vitamin D, calcium). Tips for maintaining a balanced diet while limiting dairy intake include:

  • Drink smaller amounts of milk more often. This gives the body more time to digest the smaller amounts of lactose.
  • Try different types of dairy products. If your symptoms allow it, experiment with different types of cheeses and milk products. Many lactose intolerant people can tolerate hard cheeses (e.g., Swiss, cheddar) and yogurt.
  • Drink milk at meal times. This slows the digestive process, giving the body more time to digest the lactose.
  • Use lactose-reduced or lactose-free products. Many types of dairy products are also available in this more easily digested form.
  • Look for other sources of calcium. Other types of foods can be good sources of calcium, particularly:
    • Broccoli, collard greens and kale
    • Canned salmon
    • Sardines
    • Almonds
    • Oranges and calcium-fortified orange juice
    • Some tofu
    • Soy milk
    • Some bread 
    • Some juices
    • Molasses

Since the body requires vitamin D to absorb calcium, patients should also be sure to provide themselves with an adequate supply of the vitamin. Dietary sources of vitamin D include eggs and liver. Exposure to sunlight also enables the body to produce the vitamin.  

  • Use a dietary supplement. Dietary supplements are available to individuals who find it difficult to get enough nutrients in their diet while limiting their intake of dairy. An individual should consult their physician to determine what type of supplements might be necessary. Both calcium and vitamin D can be easily replaced with supplements.

Questions for Your doctor on milk intolerance

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about milk intolerance:

  1. Do my symptoms suggest milk intolerance?
  2. What method will you use to determine if I suffer from milk intolerance?
  3. What may have caused me to develop this condition?
  4. Does milk intolerance pose any danger to my overall health?
  5. What are my treatment options?
  6. What foods/ingredients should I avoid? Are there some dairy products that are less likely to cause symptoms?
  7. Can I continue to eat dairy products if I use a lactase pill?
  8. Is it safe for me to eat small amounts of dairy?
  9. Should I take a calcium supplement?
  10. Are my children likely to develop milk intolerance as well?
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