Lactose intolerance has both genetic and non-genetic causes. Lactose intolerance can happen at any age. Learn the basics of lactose intolerance and how it could affect your health.

People with lactose intolerance are unable to fully digest sugars found in dairy products. There are many reasons people become lactose intolerant, and genetics may play a role.  According to the U.S. National Library of Medicine, about 65 percent of the world population (or nearly 5 billion people) are lactose intolerant. In East Asia, the number is more than 90 percent.

Know Your Health: The Genetics of Lactose Intolerance

Lactose intolerance is the inability to eat dairy without having an adverse reaction. It occurs when the body doesn’t produce enough of an enzyme that aids in the digestion of sugars found in dairy. Learn about the different types of lactose intolerance, genetic disposition, how it is diagnosed, and how to manage it with this guide:

  • What is Lactose Intolerance?
    • Types of Lactose Intolerance
    • Lactose Intolerance Symptoms
    • Am I Lactose Intolerant?
  • What Causes Lactose Intolerance?
    • Is Lactose Intolerance Genetic?
    • Is Lactose Intolerance Inherited?
    • Can You Become Lactose Intolerant?
    • Lactose Intolerance Risk Factors
  • Lactose Intolerance Test — How It’s Diagnosed
    • Lactose Intolerance Management

What is Lactose Intolerance?

Lactose intolerance is the inability to fully digest sugars found in dairy products. Lactase is an enzyme produced in the small intestine that breaks down sugars in dairy products into the simple sugars glucose and galactose, which are absorbed into the bloodstream as fuel. Lactose-intolerant people do not generate enough lactase for the process to work.

With lactase in low production, the undigested lactose passes into the colon where it interacts with bacteria. This interaction causes the typical symptoms of lactose intolerance, which are bloating, gas, stomach cramps, diarrhea, nausea, and sometimes vomiting.

Milk allergies, while similar, are less common and have symptoms with the potential to be far more severe with violent vomiting, bloody stools, and anaphylactic shock. Milk allergies often appear early in life, while lactose intolerance generally appears in adulthood.

Types of Lactose Intolerance

There are four distinct types of lactose intolerance. Two are genetically predisposed, one is often temporary, and the fourth is usually brought on by illness or injury.

  • Primary lactose intolerance is the most common type. Most people with primary lactose intolerance are genetically predisposed to significantly reduce lactase production between the ages of 2 and 5. As enzyme levels decrease, dairy becomes harder to digest and symptoms arise. Symptoms may not show until adulthood.
  • Secondary lactose intolerance is caused by an injury or illness. Any negative impact to the small intestine can cause less production of lactase. Diseases, such as Crohn’s and celiac, are commonly linked to this type of lactose intolerance. Surgery, medication, or chemotherapy can also hinder production of the enzyme. This type of lactose intolerance can be temporary or permanent.
  • Developmental lactose intolerance occurs in babies who are born prematurely. It usually resolves after the baby’s small intestines are fully developed.
  • Congenital lactose intolerance is the rarest type. It occurs when a baby is born with little to no lactase production in the small intestine. This genetic disorder can only be passed to a baby if both parents have the mutated gene.

Lactose Intolerance Symptoms

Symptoms and severity vary depending on the type of lactose intolerance and how much dairy was consumed. Typically, the following symptoms hit within a few hours of ingesting dairy:

  • Stomach cramps
  • Bloating
  • Diarrhea
  • Gas
  • Nausea
  • Pain in the abdomen
  • Vomiting
  • Stomach rumbling

Am I Lactose Intolerant?

People who experience any of the symptoms listed above after eating dairy may be lactose intolerant. Whether you have one of the symptoms or all of them, you should seek medical treatment or advice from a physician if you are uncomfortable or over-the-counter medications do not work.

What Causes Lactose Intolerance?

The most common type of lactose intolerance, primary lactose intolerance, is the result of an inherited genetic trait that runs in families. When a baby stops breastfeeding, the genetic response is to decrease the expression of the LCT gene, which provides instructions for making lactase in the small intestine. When lactase-producing cells line the walls of the small intestine, they help absorb nutrients as food passes through. Without this enzyme, lactose is broken down by bacteria inside the colon, which causes the symptoms of lactose intolerance.

Is Lactose Intolerance Genetic?

The type of lactose intolerance a person suffers from determines whether genes play a role or not. For primary lactose intolerance, the most common form, genetics do play a role. Located within chromosome 2, the MCM6 gene helps control the activity or expression of the LCT gene.

The ability to tolerate lactose depends on the type of MCM6 variant a person has. The LCT gene follows the instructions provided by MCM6 and either produces adequate lactase to digest milk or not enough. For babies born with congenital lactose intolerance, the MCM6 gene is responsible to little or no lactase production at birth.

Can You Become Lactose Intolerant?

Lactose intolerance can be triggered by injury, illness, medication, or surgery. Any negative impact to the small intestine can trigger lactose intolerance. This type of lactose intolerance can be temporary or permanent. Primary lactose intolerance can set in later in life, usually once an individual reaches adulthood.

Lactose Intolerance Risk Factors

Lactose intolerance can happen at any time for a myriad of reasons. For example, taking antibiotics or having a bout of diarrhea can interfere with the small intestine’s ability to produce lactase. Below are the most common risk factors associated with having any of the four forms of lactose intolerance:

  • Crohn’s disease
  • Celiac disease
  • Injury
  • Surgery
  • Aging
  • Medication
  • Chemotherapy
  • Antibiotics
  • Diarrhea

Lactose Intolerance Test — How It’s Diagnosed

If you get the same symptoms after consuming dairy products, you should discuss the symptoms with your doctor. A doctor can administer a hydrogen breath test. Normally, hydrogen gas is barely detectable in the breath, but if you are lactose intolerant, you will have undigested dairy products fermenting in the colon, which produce hydrogen. The test takes about two to three hours and begins with drinking a lactose-heavy beverage. Afterwards, the patient’s breath is analyzed at regular intervals to determine the amount of hydrogen. Hydrogen is detectable at higher levels if someone is lactose intolerant.

Genetic tests are also available to analyze some forms of lactose intolerance. Additionally, a doctor can do more invasive procedures, such as an endoscopy, to view the inside of the intestines with a camera or take tissue samples from the inside of the gut.

Lactose Intolerance Management

While there is no cure for lactose intolerance, there are successful ways to manage the condition. The simplest way is to avoid dairy products that trigger bouts of discomfort. It’s still possible for some lactose-intolerant people to eat dairy products on occasion if a few rules are followed to avoid discomfort.

Eating small amounts of dairy products with other non-lactose foods can sometimes help you successfully deal with the side effects. The type of lactose-rich foods chosen can make a difference. Yogurt is generally easier to digest than milk. Supplements that help digest lactose are also available to take before eating dairy. Be sure to consult a doctor before adding any supplements to a diet.

Although great strides have been made in deciphering the genetics of lactose intolerance, more research needs to be done to better understand how to treat and manage the condition. As we understand more about the genetics of the human body, new research will lead to scientific breakthroughs to help people with lactose intolerance. You can directly contribute to health research with your unique health data, which enables the research needed to find treatments and cures to not only lactose intolerance, but other ailments as well.

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