Lactose intolerance – what are the symptoms and causes?

Lactose intolerance is a common digestive disorder resulting from a deficiency of the enzyme lactase, which is responsible for breaking down the sugar found in milk and dairy products. Symptoms usually appear after consuming dairy products and can significantly affect quality of life. Although it is not life-threatening, its chronic symptoms can lead to the avoidance of dairy products, which in turn can result in nutritional deficiencies.

1. Symptoms associated with intolerance
2. Etiology of intolerance
3. Long-term effects
4. Combating lactose intolerance

Symptoms associated with intolerance

The symptoms of lactose intolerance are the result of undigested lactose being fermented by intestinal bacteria in the colon, leading to the production of gases and organic acids. The most common symptoms are therefore bloating, abdominal pain, excessive flatulence, diarrhoea and a feeling of fullness in the abdomen. The severity of symptoms depends on the amount of lactose consumed and individual tolerance.

Diagnosis

Diagnosis is based on hydrogen breath tests, which measure the amount of hydrogen in exhaled air after lactose consumption – elevated levels indicate lactose fermentation in the large intestine. Another method, although less specific, is the lactose tolerance test, which measures blood glucose levels after lactose consumption. A lack of increase in glucose levels may suggest intolerance, but there are many external factors that can potentially distort the clinical picture.

In children

In children, stool pH tests are also used, where an acidic reaction indicates the presence of undigested lactose. In some cases, a small intestine biopsy is performed to directly measure lactase activity. It is worth noting that the symptoms of lactose intolerance can be confused with other conditions, such as irritable bowel syndrome or milk protein allergy.

Etiology of intolerance

The causes of lactose intolerance are varied and can be both genetic and acquired. Primary lactose intolerance results from a physiological decline in lactase activity after infancy, which is common in many populations around the world. Secondary lactose intolerance may result from damage to the small intestine mucosa, for example in the course of coeliac disease, Crohn's disease or after intestinal infections. There is also a rare, congenital form of lactose intolerance caused by genetic mutations, leading to a complete lack of lactase from birth.

Long-term effects

The long-term effects of lactose intolerance may include the risk of calcium and other nutrient deficiencies. This mainly refers to osteopenia or osteoporosis, which threaten bone mass. In addition, avoiding dairy products can affect the gut microbiota, reducing the diversity of bacteria that are beneficial to health. In some cases, there is also a negative impact on quality of life, resulting from the need for a restrictive diet and fear of symptoms occurring after accidental lactose consumption.

Main sources of lactose

Combating lactose intolerance

Managing lactose intolerance is based on an individual approach that takes into account the degree of intolerance and the patient's nutritional needs.

Diet

The basic strategy is to limit lactose intake by eliminating or reducing the amount of dairy products in the diet. Lactose-free dairy products or mature products such as hard mature cheeses are an alternative.

Lactase supplements

The use of preparations containing the lactase enzyme can aid lactose digestion and alleviate gastrointestinal symptoms, especially in people who do not want to completely eliminate dairy products from their diet.

Probiotics, calcium and vitamin D

Some research suggests that probiotics, particularly Lactobacillus and Bifidobacterium strains, i.e. lactic acid bacteria (LAB), may improve lactose tolerance by modulating the gut microbiota and increasing the activity of lactase produced by microorganisms. Literature reviews also indicate that regular consumption of probiotics may reduce the severity of some symptoms of lactose intolerance. It is also important to monitor nutritional status and, if necessary, supplement with calcium and vitamin D to prevent deficiencies resulting from limiting dairy products in the diet.

Sources:

• Borralho AI, Marcos P. Lactose Intolerance and Malabsorption Revisited: Exploring the Impact and Solutions. GE Port J Gastroenterol. Published online April 21, 2025. doi:10.1159/000545923
• Aierken K, Xu Z, Ma J, Kawuli G. The efficacy of low/lactose-free milk powder in the treatment of lactose intolerance in infants: A protocol for systematic review and meta analysis. Medicine (Baltimore). 2024;103(31):e39098. doi:10.1097/MD.0000000000039098
• Vandenplas Y, Broekaert I, Domellöf M, et al. An ESPGHAN Position Paper on the Diagnosis, Management, and Prevention of Cow's Milk Allergy. J Pediatr Gastroenterol Nutr. 2024;78(2):386-413. doi:10.1097/MPG.0000000000003897
• Leis R, de Castro MJ, de Lamas C, Picáns R, Couce ML. Effects of Prebiotic and Probiotic Supplementation on Lactase Deficiency and Lactose Intolerance: A Systematic Review of Controlled Trials. Nutrients. 2020;12(5):1487. Published 2020 May 20. doi:10.3390/nu12051487