What Causes Lactose Intolerance in Humans?

Lactose is a disaccharide or sugar molecule found in milk and most dairy products. It is broken down into two smaller molecules namely glucose and galactose by an enzyme called lactase. This enzyme is found in the small intestine and helps lactose to be absorbed into the bloodstream and used by the body.

Individuals who are not able to produce an adequate amount of lactase tend to develop lactose intolerance because their bodies cannot completely digest lactose. This leads to symptoms like bloating, flatulence, abdominal pain and diarrhoea. Although this condition is common and usually harmless, it could cause a lot of discomfort and inconvenience.

Lactase deficiency, despite being prevalent in most people, does not always have the same effect on everyone. Some have a severe case of lactose intolerance that they need to completely eliminate lactose from their diets, while there are those who only experience mild and manageable symptoms. Individuals who are not lactose intolerant can consume milk and dairy just fine even with low amounts of lactase in their bodies.

Types and corresponding causes of lactose intolerance

Lactose intolerance has four types, with various factors influencing the lactase deficiency responsible for each type.

Primary lactose intolerance

This is the most common type of lactose intolerance and it is due to a natural physiological progression called lactase non-persistence where the body produces less lactase after infancy up to 21 years of age. Its occurrence is genetically determined and is largely based on one’s ethnicity with Asians, Africans and Southern Europeans at the highest risk.

Secondary lactose intolerance

This kind of lactose malabsorption is a result of a disease or an operation that caused damaging effects on the small intestine impairing its ability to produce lactase. Some diseases related to secondary lactose intolerance are Crohn’s disease, coeliac disease and small intestinal bacterial overgrowth (SIBO).

Congenital lactose intolerance

This is a rare type of lactose intolerance also referred to as congenital alactasia. It is inherited through a disorder called autosomal recessive where both parents pass on the abnormal gene carrying the disease to their offspring. Babies born with this condition are unable to produce lactase in their bodies making it difficult for them to digest milk. As a result, they could have a severe case of diarrhoea and become extremely dehydrated and malnourished.

Developmental lactose intolerance

This is a temporary condition in premature babies as their intestines have not yet fully developed, but it will eventually improve as they mature.

What are the signs and symptoms of lactose intolerance?

Below are signs and symptoms indicative of lactose intolerance. These symptoms usually manifest 30 minutes to two hours after ingesting milk and other dairy products:

  • Indigestion
  • Flatulence/gas
  • Bloating caused by distention
  • Abdominal cramps
  • Diarrhoea
  • Constipation, though less common than diarrhoea
  • Nausea
  • Vomiting, on some occasions

The manifestations, as well as the severity of the symptoms of lactose intolerance, may be different for every person depending on the amount of lactose each individual consumes or how much lactase one is able to produce. In other words, some people who are lactose intolerant can ingest lactose in small amounts without triggering any adverse reactions, while others who eat very little dairy still experience severe symptoms. Additionally, the unique bacterial composition in people’s intestines could affect the way their digestive systems respond to lactose in their bodies.

Unfortunately, these symptoms can also point to other digestive disorders and diseases so they are not enough basis for diagnosing whether one has lactose intolerance or not.

What happens when lactose is not digested?

When lactose is not digested by lactase in the small intestine, it travels into the colon where it is fermented by gut bacteria. This process yields hydrogen gas resulting in flatulence, bloating and other symptoms mentioned earlier. Moreover, some of the hydrogen produced in the colon make their way to the lungs and then expelled in the breath.

Lactose that remains undigested in the colon develops an osmotic effect attracting water into the large intestine and causing stool to become very soft and loose. These stools are then eliminated by the body as diarrhoea.

How is lactose intolerance diagnosed?

There are several ways to find out if you are lactose intolerant. A few of the more common and reliable ones are:

Milk Challenge

The simplest test is the milk challenge where a person suspected of lactose intolerance fasts overnight, then drinks a specified amount of milk in the morning and takes nothing else for another three to five hours. During this period, the person is monitored to see if symptoms of lactose intolerance occur.

Elimination Method

Another way to diagnose lactose intolerance is the elimination method in which milk and dairy are temporarily removed from a person’s diet for a few weeks then observing if the absence of lactose brings about symptomatic relief or improvement. This method should only be performed under the supervision of a qualified medical practitioner or dietitian.

Hydrogen Breath Test

This test involves fasting overnight and ingesting 16 ounces (or 25 grams) of pure lactose the following morning. As stated earlier, people who are lactose intolerant are unable to break down lactose in their small intestines, leaving the lactose to reach the colon untouched, where it is fermented by gut bacteria, producing hydrogen in the process. This gas then travels up to the lungs and is expelled in the breath. Three to five hours after ingesting lactose, breath samples are collected in intervals of 10 to 15 minutes and analysed for traces of hydrogen. A high amount of hydrogen gas detected in the breath is indicative of lactose intolerance.

How is lactose intolerance treated?

Modifications in dietary composition and lactase enzyme supplements as well as treating any intestinal ailments with the help of a doctor or a specially trained dietitian may significantly improve and alleviate its symptoms. In addition, gradually re-introducing lactose-containing foods and incrementally increasing your consumption of lactose after eliminating it from your diet may eventually develop your tolerance for it.

Furthermore, working closely with doctors and qualified medical practitioners may be beneficial to lactose-intolerant individuals, especially in ensuring that they still get the right amount of nutrients like calcium and vitamin D that are normally obtained from milk and dairy products.

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