Ever seen people asking for “lactose-free milk” in the store? Chances are, they or someone in their family has lactose intolerance. Experts believe that around 75 percent of the world’s population has lactose intolerance. Lactose intolerance, also known as alactasia, hypolactasia, milk sugar intolerance and lactose malabsorption is a digestive disorder. It is the inability to digest lactose due to the lack of an enzyme called lactase in the digestive system. Lactose intolerance mainly affects adults and people above the age of 5. Children under five rarely develop lactose intolerance.

Lactose is a carbohydrate, a disaccharide to be precise, which is commonly found in milk and other dairy products. This sugar consists of galactose and glucose subunits.

Structure of Lactose. Image Credit: Researchgate

Cause of Lactose Intolerance

Lactase is an enzyme that is produced in the small intestine of humans and other mammals. Lactase is responsible for lactose breakdown. Usually, when someone eats food containing lactose, the lactose is broken down into simple units of galactose and glucose in the small intestine by the act of the enzyme lactase. Then they’re absorbed in the bloodstream.

People with lactose intolerance simply cannot produce enough lactase, so they’re unable to break down any food containing lactose. There are four types of lactose intolerance. We will describe each of them individually.

  1. Primary Hypolactasia: Primary alactasia, also known as primary lactose Intolerance, occurs due to the inability to produce enough lactase. As people age, their ability to product lactose may decrease resulting in lactose intolerance. That’s why it is common among adults to have lactose intolerance. Genes largely influence primary lactose intolerance. Thus, it is very common among people from African, Hispanic, and Southern European descent.
  2. Secondary Hypolactasia: It is also known as secondary lactose intolerance, which occurs when the intestinal epithelial cells in the lining of the small intestine are damaged. It can be due to surgery, infection or illness. Secondary lactose intolerance is usually temporary but it may become permanent if not cured.
  3. Developmental Lactose intolerance: It occurs in premature infants and goes away within a few weeks. The small intestine develops cells that can produce lactase during the late pregnancy period.
  4. Congenital lactose intolerance: In this case, an infant is unable to produce lactase by birth. It is a genetic disorder and caused by a mutation in the LCT gene, which contains the instruction for making lactose. This is a rare occurrence; both of the parents must have mutations in the same gene for their child to have congenital lactose intolerance.

Also, in some rare cases, lactose intolerance can arise from milk allergy in adults.


The symptoms of lactose intolerance shows up within some hour of eating lactose-containing food. The severity of the symptoms varies from person to person. Some of the common symptoms of lactose intolerance are:

  1. Nausea
  2. Vomiting
  3. Weird sound from the stomach and stomach cramps
  4. Diarrhea
  5. Abdominal distention
  6. Flatulence
  7. Bloating

Some people may show signs of alactasia due to medication as some drugs use lactose as a filler. It is a sporadic case as drugs contain a minute amount of lactose. It may occur when someone with severe lactose intolerance takes drugs containing lactose.

Risk Factors

Several risk factors contributes to lactose intolerance. Some of them include:

  1. Age: As people age, their ability to produce lactase decreases dramatically, which contributes to alactasia.
  2. Illness: Some diseases, celiac disease, for example, can damage the lining of the small intestine which produces lactase.
  3. Ethnicity: Lactose intolerance is prevalent among Asian, African, Native American, Hispanic and South European descent.
  4. Side effects: Chemotherapy in cancer treatment can damage the intestinal epithelial cells, which increases the chance of developing alactasia.
  5. Premature birth: Infants born too early have a higher chance of being born with alactasia.


A physician can perform various diagnostic procedures such as breath test, genetic test, blood test, an intestinal biopsy to diagnose alactasia.

What to do if you diagnose positive with Lactose Intolerance?

Some people can still tolerate a small amount of milk or dairy product. Usually, people do better if they combine dairy food with other diets, while others have to give up milk completely. So it differs from person to person, the only way to find out if you can still take a tiny amount of milk product is to eat them in a small amount and see if you develop any symptoms.

Dairy diets are rich in calcium and other nutrients, so if you give up milk completely you have the risk of developing osteoporosis in late adulthood. You can substitute dairy diet with other foods rich in calcium in nutrients. Beef liver, fortified orange and soy milk, egg yolk, tofu and almonds are some nutrients rich foods you can take instead of milk.


  1. Lactose Intolerance. Retrieved from https://www.niddk.nih.gov/health-information/digestive-diseases/lactose-intolerance on 04/29/2020
  2. Lactose intolerance. Retrieved from https://ghr.nlm.nih.gov/condition/lactose-intolerance on 04/29/2020
  3. Overview-Lactose intolerance. Retrieved from https://www.nhs.uk/conditions/lactose-intolerance/ on 04/29/2020
  4. What Is Lactose Intolerance?. Retrieved from https://www.webmd.com/digestive-disorders/digestive-diseases-lactose-intolerance#1 on 04/29/2020
  5. Lactose Intolerance 101 — Causes, Symptoms and Treatment. Retrieved from https://www.healthline.com/nutrition/lactose-intolerance-101 on 04/29/2020
  6. Lactose Intolerance. Retrieved from https://www.mayoclinic.org/diseases-conditions/lactose-intolerance/symptoms-causes/syc-20374232 on 04/29/2020
  7. Lactose intolerance: What you need to know. Retrieved from https://www.medicalnewstoday.com/articles/180120 on 04/29/2020

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