In lactose intolerance – colloquially called lactose intolerance – (synonyms: Alactasia; Hypolactasia; Lactose malabsorption; Lactose deficiency syndrome; Lactose intolerance; Lactase deficiency; Lactose intolerance; Lactose intolerance syndrome; Lactose malabsorption; Lactose deficiency syndrome; Food intolerance; Milk sugar intolerance; ICD-10-GM E73.-: Lactose intolerance), the affected person cannot tolerate lactose (milk sugar).
This is a utilization disorder in which the activity of the disaccharidase lactase is reduced or completely absent. Disaccharidases are enzymes and have the task of splitting the disaccharides (twofold sugars) ingested with food or formed during the digestion of complex carbohydrates into the monosaccharides (single sugars) glucose and galactose. The following forms are to be distinguished:
- Primary lactase deficiency – is divided into two forms:
- Hereditary (congenital). Lactase deficiency – autosomal recessive inheritance; manifests already in newborns; very rare form.
- Acquired lactase deficiency – after weaning, the enzyme activity falls continuously with age (physiological aging process); most common form.
- Secondary lactase deficiency – temporary lactase deficiency due to damage to the mucosa of the small intestine (small intestinal mucosa), e.g. in celiac disease (gluten-induced enteropathy), Crohn’s disease.
A symptomless lactose intolerance is called lactose malabsorption. Here, uncleaved lactose enters the large intestine, but does not lead to abdominal discomfort (gastrointestinal symptoms).
Hereditary lactase deficiency is extremely rare and causes diarrhea (diarrhea) even in infants. The cause of hereditary lactase deficiency is a genetic defect, whereby the enzyme lactase is absent from birth or can only be produced to a very low degree (alactasia). Only a dozen cases of this disease have been described worldwide.
Premature babies (before 37 weeks of gestation) sometimes have lactose intolerance. Lactose intolerance in Caucasians often affects children older than 5 years.
Acquired lactase deficiency (primary lactase deficiency) is the most common form of lactose intolerance. The prevalence (disease frequency) is 7-22% (in Germany). Lactase activity decreases continuously with increasing age. The causes of this are still largely unknown. It is suspected that age-related changes in the intestinal mucosa surface (surface of the intestinal mucosa) impair the activity of lactase. Furthermore, damage to the mucosa of the small intestine (small intestinal mucosa) by viral infections is discussed.
Secondary lactase deficiency can be the consequence of a primary intestinal disease. Lactose intolerance often occurs in celiac disease (gluten-induced enteropathy). With complete abstinence from the specific food components, the primary disease heals and the secondary deficiency regresses. Lactase deficiency also develops in many cases after gastric resection (partial stomach removal) due to the non-physiological burden on the small intestine (dysbiosis).
Course and prognosis: Lactose tolerance varies from person to person and depends on the individual lactase test activity. The minimum tolerated amount of lactose must therefore be determined on an individual basis. In many cases, lactose intolerance cannot be cured, so those affected have to follow a low-lactose or lactose-free diet for the rest of their lives. It is important to ensure adequate calcium intake so that the risk of osteoporosis (bone loss) is not increased by avoiding or restricting the consumption of milk and dairy products. In the case of secondary lactose intolerance, serious complications are not to be expected. In this case, the focus is on treatment of the underlying disease.