Lactose Intolerance

BASICS

Lactose intolerance is a syndrome of abdominal pain, bloating, and flatulence after the ingestion of lactose.
Lactose malabsorption results from a reduction in lactase activity in the brush border of the small intestinal mucosa.
Lactase activity peaks at birth then decreases after the first few months of life, declining continuously throughout life. 75% of adults worldwide exhibit a decline in lactase activity after birth. Only 50% of lactase activity is needed to digest lactose without causing symptoms of lactose intolerance.
- Congenital lactose intolerance is very rare
- Primary lactose intolerance is relatively common in adults who develop low lactase levels 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)
Lactose malabsorption may be asymptomatic and is equally common in healthy patients and in those with functional bowel disorders.
System(s) affected: endocrine/metabolic, gastrointestinal

Pediatric Considerations

Primary lactose intolerance begins in late childhood.
No consensus on whether young children (<5 years of age) should avoid lactose following diarrheal illness
Lactose-free formulas are available.
Exclude milk protein allergy.

≥50% of infants with acute or chronic diarrheal disease have lactose intolerance; particularly common with rotavirus infection
Lactose intolerance is also common with giardiasis, ascariasis, irritable bowel syndrome (IBS), tropical and nontropical sprue, and AIDS malabsorption syndrome.

In South America, Africa, and Asia, rates of lactose intolerance are >50%.
In the United States, the prevalence is 15% among whites, 53% among Hispanics, and 80% among African Americans.
In Europe, lactose intolerance 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

Primary lactose intolerance: The normal decline in lactase activity in the intestinal mucosa is genetically determined and permanent after weaning from breast milk.
Secondary lactose intolerance: associated with gastroenteritis in children; also associated with any gastrointestinal infection or inflammation of the small intestine with resultant lactose malabsorption in both adults and children

In whites, lactase deficiency is associated with a single nucleotide polymorphism (SNP) consisting of a nucleotide switch of T for C 13910 bp on chromosome 2. This results in variants of CC-13910 (lactase nonpersistence) or CT-13910/TT-13910 (lactase persistence) (1). SNP (C/T-13910) is associated with lactase persistence in northern Europeans.
Other SNPs (G/C-14010, T/G-13915, and C/G-13907) linked to lactase persistence in some of African descent.

Adult-onset lactase deficiency has wide geographic variation.
Age:
- Signs and symptoms usually do not become apparent until after age 6 to 7 years.
- Symptoms may not be apparent until adulthood, depending on dietary lactose intake and rate of decline of intestinal lactase activity.
- Lactase activity correlates with age, regardless of symptoms.

Lactose avoidance relieves symptoms. Patients can learn what level of lactose is tolerable in their diet.

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