Lactose Intolerance: Causes, Symptoms and Treatments

What are the causes of lactose intolerance?

According to a study, close to 75% of the world's population is affected by lactose intolerance. A research on the update on lactose malabsorption and intolerance suggests, there are 3 main types of lactose intolerance:

Congenital Lactose Intolerance

Lactose intolerance can be caused by genes as some people are born with a poorer ability to produce lactase. Preterm infants have a high tendency to develop lactose intolerance because their digestive system may not be fully developed when they are born.

Primary Lactose Intolerance

Lactose intolerance rarely occurs during infancy because full-term infants are usually born with sufficient lactase to prepare for digestion of lactose in breastmilk. In most cases, lactose intolerance develops over time as lactase production decreases with age. Symptoms of lactose intolerance usually appear after childhood (after 5 years old). 

Secondary Lactose Intolerance

Lactose intolerance may also be caused by a virus or infection, which inflicts temporary damage to the small intestine due to inflammation in the intestinal wall, consequently reducing lactase production. Once the virus is cleared from the body, the symptoms of lactose intolerance will be lifted as well. 

Occasionally, lactose intolerance occurs in parallel with other diseases, in particular gastroenteritis and celiac disease.

What are the risk factors of lactose intolerance?

According to a study by Purdue University, risk factors of lactose intolerance include:

• Age: lactose intolerance is more common in adults but less in children or infants.
• Ethnicity: lactose intolerance is very common amongst Asian and African populations, and within specific races such as Spaniards, Mediterranean, Southern Europeans, and American Indians.
• Premature birth: preterm infants have less lactase because the lactase-producing cells in the small intestine only begin to develop in the third trimester of pregnancy.

What are the symptoms of lactose intolerance?

Symptoms usually appear 30 minutes to 2 hours after eating or drinking foods that contain lactose, i.e. milk and dairy products. The severity of the symptoms usually depends on the amount of lactose intake and the effectiveness of enzymatic action in the body. 

Under lactose intolerance, lactose in milk and dairy products cannot be completely digested and absorbed in the digestive tract. As a result, most water is retained in the digestive tract to form watery stool which passes out as diarrhea. The undigested lactose then enters the large intestine, in which gut bacteria ferment the unabsorbed lactose and produce gases like carbon dioxide and hydrogen, as well as other byproducts that act as laxatives. Eventually, it brings about digestive signs and symptoms such as nausea, bloating, abnormal bowel movement, abdominal pain and farting.

How to treat people with lactose intolerance?

While severe consequences like dehydration, electrolyte imbalance and malnutrition are rarely caused by lactose intolerance, there is no cure for lactose intolerance. No known treatment to date can increase the production of lactase in the body. Most people with lactose intolerance usually avoid the digestive symptoms by cutting down on milk and dairy products. Also, certain medications and supplements can mediate the symptoms of lactose intolerance. 

However, milk and dairy products are important sources of protein, calcium and vitamin D, which are essential for growth and development. In fact, according to research, many people with lactose intolerance can tolerate small amounts of lactose, up to 18g to be exact, if the intake is distributed throughout the whole day. So even for people with lactose intolerance, they may be able to enjoy some milk and dairy products. Some people may be more adapted to a certain dairy product and can tolerate a certain level of lactose intake. A clinical trial study even found that people with lactose intolerance can be trained gradually to adapt to dairy products, but it is important to keep the intake low in the beginning, then increase progressively.

Medication

Lactase enzyme supplements can be added into milk and dairy products to ease lactose digestion in people with lactose intolerance, so that they can still eat or drink dairy products with minimal symptoms of lactose intolerance.

Food to be aware of

People with lactose intolerance are suggested to be cautious of foods that contain lactose, particularly dairy products. For example, milk, ice cream, cheese, yogurt and butter. 

Certain foods may contain some lactose even though they are not dairy products by definition. For example, breakfast cereals, breads and baked goods, chocolate and confectionery, biscuits and cookies, desserts, etc.

Check the ingredients before consuming food items to see if it contains milk or other sources of lactose.

Alternatives for people with lactose intolerance

Dairy products contain many essential nutrients, including calcium and vitamin D, which is important for growth and development. Alternatively, people with lactose intolerance may choose foods with non-dairy sources of calcium and/or vitamin D. For example, lactose-free milk, yoghurt and cheese, as well as tofu, boned fish and many vegetables etc. These foods contain either natural or fortified calcium and/or vitamin D.