Lactose intolerance: a digestive disorder linked to lactose

Lactose intolerance is a digestive disorder that manifests after the intake of lactose (the sugar of the milk). The cause of this disorder is the deficit of lactase, which is an enzyme that is expressed in the small intestine its function consists of degrading lactose to generate glucose and galactose.

A lack of lactase makes it difficult (or impossible) to break down lactose and absorb its components. As a result, lactose accumulates in the intestine, and instead of being digested and absorbed, it is fermented by intestinal microbiota, leading to the production of gases (mainly hydrogen and methane).

The accumulation of these gases causes the characteristic symptoms of lactose intolerance, which include:

• Abdominal cramps
• Abdominal bloating
• Flatulence (gas)
• Diarrhea
• Constipation and burning sensation during defecation

Depending on the cause of the lactase deficiency, it can be classified as:

• Primary: caused by the physiological decline of lactase production that occurs with age in all mammals. However, in humans, genetic mutations have allowed the production of lactase to continue into adulthood
• Secondary: caused by other diseases that damage the intestinal wall and, consequently, alter lactase levels. These include celiac disease, gluten intolerance, Crohn’s disease, and gastrointestinal infections, among others. Allergic reactions and certain medications can also lead to secondary lactase deficiency
• Congenital: a rare condition in which lactose intolerance manifests from birth due to the complete absence of lactase. This disorder is hereditary and follows an autosomal recessive inheritance pattern (meaning both parents must pass on the same genetic variant for the baby to be affected)

Certain factors increase the risk of developing lactose intolerance, including:

• Advanced age: lactase levels naturally decline with age, making older adults more prone to developing primary lactase deficiency
• Ethnic origin: lactose intolerance is more common in individuals of African, Asian, Hispanic, or Native American descent
• Premature birth: premature babies may have reduced lactase levels because the small intestine does not produce lactase-producing cells until late in the third trimester
• Diseases affecting the small intestine: these can lead to secondary lactase deficiency
• Certain cancer treatments: radiation therapy and chemotherapy targeting gastrointestinal cancers can increase the risk of lactose intolerance

Several tests can be used to diagnose lactose intolerance, including:

• Glucose response to lactose load: measures blood glucose levels every 30 minutes over 2 hours after consuming a lactose-rich drink. If blood glucose levels do not rise during the test, lactase deficiency may be suggested. However, this test is non-specific, as other conditions (e.g., diabetes or malabsorption disorders) can affect results
• Hydrogen breath test: measures hydrogen levels in the patient’s exhaled breath before and after consuming a lactose-rich drink. Hydrogen is produced when intestinal bacteria ferment unabsorbed lactose. Elevated hydrogen levels suggest lactase deficiency. This test is quick and reliable for detecting lactose malabsorption
• Stool acidity test: measures the pH of stool samples. Lower pH indicates higher acidity, which correlates with elevated hydrogen levels. This test is particularly useful for diagnosing lactose intolerance in young children, for whom other diagnostic methods may be risky or impractical
• Small intestine biopsy: involves collecting a tissue sample from the small intestine for microscopic examination to detect abnormalities in lactose absorption. This test is typically used to confirm intolerance following elevated hydrogen levels in the breath test
• Genetic testing: identifies specific polymorphisms in the lactase gene to assess its expression, which affects lactase levels

Lactose intolerance is not a severe condition. Reducing the consumption of lactose-containing foods or using lactase enzyme pills or drops to aid digestion is usually sufficient to manage the disorder. In some cases, calcium supplements may be recommended since dairy products are the primary source of calcium for most people.

There is no effective way to prevent lactose intolerance, as it develops due to genetic factors and aging. The only way to prevent symptoms is to avoid lactose-containing foods and beverages.