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Lactase Deficiency and Lactose Intolerance

Lactose intolerance occurs when the cells that line the small intestine are unable to produce enough of the enzyme lactase, which is needed to break down the milk sugar lactose into the simple sugars glucose and galactose that the body can absorb. Lactose intolerance, which is sometimes wrongly called milk intolerance, is not the same as a milk allergy. Unlike milk allergy, lactose intolerance does not involve the immune system, a key player in all types of allergic reactions. An estimated 5-10% of people of European origin but as many as 75% of Black Africans and 90% of East Asians are intolerant to lactose to some degree.

When the small intestines do not produce enough lactase to break down all the lactose, we speak of lactase deficiency. This condition can be the result of damage sustained to the lower intestine (e.g., through viral infection, stomach flu, coeliac disease or surgery) or due to an inherited condition. Some lactase-deficient individuals may not experience symptoms. Those who do experience them are considered lactose intolerant. Sometimes, though rarely, a person is born without the ability to produce lactase at all.

The ability of each lactase-deficient individual to break down lactose and tolerate dairy products varies greatly. Also, different types of dairy products contain different amounts of lactose. Therefore, some individuals with lactose intolerance can eat some types of dairy without symptoms, while others must avoid dairy entirely.

Types of Lactose Intolerance

Depending on the cause and time when the condition develops, lactose intolerance is classified into three types. All of them share the same symptoms and are treated in a similar manner. They include:

  • Adult lactose intolerance. The first symptoms usually appear in the teen years. This is the most common type of lactose intolerance and is often inherited. Depending on an individual’s production of lactase, a small amount of milk may be tolerated each day. The severity of this type of lactose intolerance usually persists or slightly worsens as the person grows older.
  • Acquired lactose intolerance. This type is also known as secondary lactose intolerance and occurs when the small intestine partially or completely discontinues the production of the enzyme lactase. Secondary lactose intolerance often comes as a result of an infection (e.g., viral stomach flu) or another medical condition (e.g. coeliac disease, cystic fibrosis). This condition can occur at any age. Whether it is temporary or permanent depends on the extent of damage to the intestine.
  • Congenital lactose intolerance. This is a rare but permanent condition when babies are born without the ability to produce the enzyme lactase. Patients with this type of lactose intolerance must avoid all foods and drinks containing lactose for their entire lives.

Causes and Risk Factors for Lactose Intolerance

The following factors increase the risk of developing lactose intolerance:

  • Ethnicity. Black Africans, East Asians, Hispanics and Native Americans are much more likely to have this condition than people of northern European descent.
  • Family history. Individuals whose parents are lactose intolerant are more likely to develop this condition or be born with it.
  • Certain illnesses. Infections, such as viral stomach flu, or other illnesses, such as cystic fibrosis or celiac disease, may damage the wall of the small intestine, which can lead to developing lactose intolerance.
  • Certain medications. Patients taking certain antibiotics may develop temporary lactose intolerance.
  • Surgery. Damage to the small intestine from surgery may also cause lactose intolerance.
  • Premature birth. There is an increased risk that infants born at 28 to 32 weeks of gestation develop lactose intolerance.
  • Age. As the body ages, it gradually stops producing lactase and some individuals may thus become lactose intolerant over time.

Symptoms of Lactose Intolerance

The most common symptoms of lactase deficiency are bloating and watery diarrhea. The lactose that is not properly broken down in the small intestine passes on into the large intestine where it comes into contact with naturally occurring bacteria, which ferment the lactose. The result is the excess production of carbon dioxide, methane and hydrogen, which leads to additional bloating, flatulence and cramping. The molecules of hydrogen can travel through the bloodstream to the lungs, where they cause bad breath. Some patients may also experience nausea. The first symptoms usually appear between half an hour and two hours after ingesting milk or dairy product.

Patients who have removed milk and other dairy products from their diet may suffer from some form of calcium and vitamin D deficiency and can be at a higher risk of bone fractures. Both these nutrients should be added to the diet through other types of foods (e.g., fish, green leafy vegetables, soy).

Diagnosing Lactose Intolerance

Depending on the severity of the symptoms, several tests are used to clinically diagnose lactose intolerance and to exclude a more serious type of condition with similar symptoms (e.g., parasite infection or irritable bowel syndrome). The tests and procedures most frequently used include:

  • Elimination diet. Consists in removing the foods that contain lactose from a patient’s diet to see if symptoms of lactose intolerance persist. This test should be conducted under the guidance of a healthcare professional.
  • Milk challenge. This simple test can be used to self-diagnose lactose intolerance. The challenge involves a period of fasting (typically overnight) followed by the consumption of a single glass of milk. In case of lactose intolerance, symptoms should appear within several hours.
  • Lactose intolerance test. Measures blood sugar (glucose) levels for signs that indicate lactose intolerance after drinking a lactose-loaded beverage.
  • Hydrogen breath test. Checks for an abnormal amount of hydrogen in the patient’s breath, which is a symptom characteristic of lactose intolerance as hydrogen cannot be normally detected in the breath of healthy individuals.
  • Stool acidity test. Measures the amount of lactic acid and some other fatty acids in the stool, which are created when undigested lactose ferments in the colon. This test may also be used to look for glucose in the stool, which indicates the presence of unabsorbed lactose in the colon.

Treatment of Lactose Intolerance

The most effective treatment for lactose intolerance is to limit or completely remove lactose from the diet. Although this treatment cannot improve the body’s ability to produce lactase, it enables the patients to effectively control their symptoms. Some patients may tolerate small amounts of milk or dairy in a different form, such as hard cheese or yogurt. However, if symptoms are severe, then complete avoidance of all foods and drinks that contain lactose may be necessary.

People with lactase deficiency should watch out for foods containing hidden sources of lactose and read the ingredient label carefully on all foods and beverages to make sure milk or lactose is not present. Unexpected products that often contain lactose include:

  • Baking mixes
  • Breads
  • Candy
  • Cereals
  • Chocolate
  • Frozen dinners
  • Instant soups, potatoes and breakfast drinks
  • Lunch meats
  • Margarine
  • Medicines
  • Salad dressings

Any of the following words may also indicate the presence of lactose:

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

Many people with lactase deficiency do not need to completely avoid lactose. However, trial and error is usually the only way to find out which foods will cause symptoms and which can be tolerated.

Lactase supplements, which contain the enzyme lactase, can be taken with a dairy food to aid in digestion. But remember, they take up to 24 hours to completely break down the lactose in a food and, therefore, cannot effectively handle large amounts of lactose. In addition, some types of dairy products are also available in lactose-reduced or lactose-free versions.

Patients who are avoiding or limiting the consumption of dairy products should supplement their diets with essential nutrients they may be missing as a result (e.g., calcium, vitamins A and D). Green leafy vegetables, fish, oranges and calcium-fortified orange juice, almonds, soy foods and soy milk, some wholegrain breads, egg yolks and molasses as well as exposure to sunlight can provide the aforementioned essential nutrients.