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- Bloating, borborygmi, abdominal pain, and diarrhea due to inability to digest lactose into its constituents (glucose and galactose) secondary to low levels of the enzyme, lactase, in the brush border of the small intestinal mucosa:
- Congenital lactose intolerance: Very rare
- Primary lactose intolerance: Common in adults in whom a low level of lactase has developed after childhood.
- Secondary lactose intolerance: Inability to digest lactose caused by any condition injuring the intestinal mucosa (e.g., infectious enteritis, celiac disease, eosinophilic gastroenteritis or inflammatory bowel disease) or a reduction of available mucosal surface (e.g., resection)
- Lactase activity peaks at birth, then starts to decrease after the 1st few months of life and continuously during lifetime. However, only 50% of lactase activity is needed to digest lactose without causing symptoms of lactose intolerance.
- Lactose malabsorption results from reduction of lactase activity, but it is an asymptomatic condition, fairly common in patients with functional bowel disorders, but no more common than in healthy individuals (1).
- System(s) affected: Endocrine/Metabolic; Gastrointestinal
- Primary lactose intolerance usually begins in late childhood.
- No consensus exists on whether young children (<5 years of age) should avoid lactose following diarrheal illness.
- Lactose-free formulas are available.
- Exclude a milk protein allergy.
- ≥50% of infants with acute or chronic diarrheal disease have lactose intolerance, especially with rotavirus disease.
- Lactose intolerance also is fairly common with giardiasis and ascariasis, irritable bowel syndrome (IBS), tropical and nontropical sprue, and the AIDS malabsorptive syndrome.
- In South America, Africa, and Asia rates of lactose intolerance are >50%.
- In the US, the prevalence is 15% among whites, 53% among Hispanic Americans, and 80% among African Americans.
- In Europe, it varies from 15% in Scandinavian countries to 70% in Italy.
- Predominant age:
- Primary: Teenage and adult
- Secondary: Depends on underlying condition
- Predominant sex: Male = Female
- Race: Adult-onset lactase deficiency varies widely among countries.
- Signs and symptoms usually do not become apparent until after age 6–7 years; recent studies actually have shown that hypolactasia may begin even after age 20.
- Symptoms may not be apparent until adulthood, depending on dietary lactose intake and rate of decline of intestinal lactase activity.
- Lactase enzyme activity is highly correlated with age, regardless of symptoms.
- In Caucasian population, lactase deficiency has been associated with a single nucleotide polymorphism (SNP) consisting of a nucleotive switch of T for C 13,910 bp above the initiation codon of the gene coding for lactase enzyme on chromosome 2. This results in variants CC-13910 (lactase nonpersistence) OR CT-13910/TT-13910 (lactase persistence) (2).
- SNP (C/T-13910) is associated with lactase persistence predominantly in northern Europeans.
- Other SNPs (G/C-14010, T/G-13915, and C/G-13907) have been linked to lactase persistence in Africans.
Avoidance of lactose in large quantities will relieve symptoms. Patients can learn what level of lactose is tolerable in their diet.
- Primary lactose intolerance: Normal decline in the lactase activity in the intestinal mucosa is genetically controlled and permanent after weaning.
- Secondary lactose intolerance: Associated with gastroenteritis in children
- Secondary lactose intolerance is also associated with nontropical and tropical sprue, regional enteritis, abetalipoproteinemia, cystic fibrosis, inflammatory bowel disease, celiac disease, and immunoglobulin deficiencies in both adults and children.
Commonly Associated Conditions
- Tropical or nontropical sprue
- Inflammatory bowel disease
- Immunoglobulin deficiencies
- Celiac disease
- Cystic fibrosis