Lactase deficiency (lactose intolerance) 

Definition:

• Clinical syndrome with characteristic signs and symptoms upon consuming lactose-containing foods.

Lactose Metabolism:

• Normally, lactose is hydrolyzed into glucose and galactose by lactase enzyme in the small intestinal brush border.

Lactase Deficiency:

• Caused by primary or secondary factors.
• Leads to clinical symptoms of lactose intolerance.
• Disease severity varies among individuals.

Sources of Lactose:

• Present in dairy products, milk, and mammalian milk.

Symptoms of Lactose Intolerance:

• Abdominal bloating and pain
• Loose stools
• Nausea
• Flatulence
• Borborygmi (stomach rumbling)

Behavioral Response:

• Many avoid milk upon diagnosis or suggestion of lactose intolerance.
• Leads to consumption of specially prepared products with digestive aids.
• Adds to the healthcare burden.

Common Confusion:

• Often confused with milk allergy.
• Lactose intolerance is a gastrointestinal disorder.
• Milk allergy is an autoimmune reaction against specific milk proteins.
• Milk allergy is life-threatening and presents early in infancy.
• Lactose intolerance usually presents in adolescence or early adulthood.

Nutritional Considerations:

• Milk is rich in calcium and vitamin D.
• Prolonged avoidance of milk can result in calcium and vitamin D deficiency.

Causes

• Primary Lactase Deficiency
  • It is the most common cause of lactase deficiency
  • found in up to 70% of the world’s population, but not all of them are symptomatic
  • gradual decline in lactase enzyme activity with increasing age. 
  • Enzyme activity begins to decline in infancy, and symptoms manifest in adolescence or early adulthood. 
  • More recently, it has been observed that lactase non-persistence is of the ancestral form (normal Mendelian inheritance), and lactase persistence is secondary to mutation.
• Secondary Lactase Deficiency
  • Due to several infectious, inflammatory, or other diseases, injury to intestinal mucosa can cause secondary lactase deficiency
    • Gastroenteritis
    • Celiac disease
    • Crohn disease
    • Ulcerative colitis
    • Chemotherapy
    • Antibiotics
• Congenital Lactase Deficiency
  • There is a decrease or absence of lactase enzyme activity since birth due to autosomal recessive inheritance.
  • It manifests in the newborn after ingestion of milk. 
  • It is a rare cause of the deficiency, and its genetics are not very well known.
• Developmental Lactase Deficiency
  • It is seen in premature infants born at 28 to 37 weeks of gestation.
  •  The infant’s intestine is underdeveloped, resulting in an inability to hydrolyze lactose. 
  • This condition improves with increasing age due to the maturation of the intestine, which results in adequate lactase activity.

Epidemiology

• Lactose intolerance is a common disease
• rare in children younger than 5
• most often seen in adolescents and young adults
• 65% of the world’s population is lactose intolerant
• most common in African Americans, Hispanics/Latinos, and Asians and least prevalent in people of European descent.

Pathophysiology

• The lactase enzyme is located in the brush border of the small intestinal mucosa. 
• Deficiency of lactase results in the presence of unabsorbed lactose within the bowel. 
• This results in an influx of fluid into the bowel lumen resulting in osmotic diarrhea. 
• Colonic bacteria ferment the unabsorbed lactose-producing gas (hydrogen, carbon dioxide, and methane), which hydrolyzes lactose into monosaccharides.
• This results in an additional influx of fluid within the lumen. 
• The overall effect of these mechanisms results in various abdominal signs and symptoms.

History and Physical

• Signs and symptoms of lactose intolerance manifest 30 minutes to 1 to 2 hours after ingesting milk (dairy) products. 
• The severity of symptoms depends upon the amount of lactose consumed, the residual lactase function, and the small bowel transit time.
  • Diarrhea
  • Abdominal bloating
  • Abdominal Pain
  • Nausea and vomiting
  • Fullness
  • Flatulence

Medical Tests

• Hydrogen breath test:
  • This test measures the hydrogen content of breath after lactose ingestion. 
  • The test is positive for lactose malabsorption if the post-lactose breath hydrogen value rises >20 ppm compared with the baseline.
• Stool acidity test:
  • Unabsorbed lactose is fermented by colonic bacteria into lactic acid, which lowers the stool pH.
• Dietary elimination:
  • One way to assess the underlying illness is to eliminate lactose-containing food products, which would result in the resolution of symptoms. 
  • Resumption of symptoms with the reintroduction of these products will indicate lactose intolerance.
• Lactose tolerance test:
  • This test determines lactose absorption after ingestion of a lactose-containing liquid. Measure serial blood glucose levels after giving an oral lactose load. 
  • After obtaining a fasting serum glucose level, 50 g of lactose is administered.
  • Serum glucose level is then measured at 0, 60, and 120 minutes. 
  • Failure of blood glucose levels to rise by 20 g may indicate lactose intolerance. 
  • This test has a specificity of 96% and a sensitivity of 75%. 
  • False-negative results may occur in patients with diabetes or small bowel bacterial overgrowth. 
• Small bowel biopsy

Treatment / Management

• Dietary Modification
• Lactase Supplements

Differential Diagnosis

• Irritable bowel syndrome
• Celiac disease
• Tropical sprue
• Cystic fibrosis
• Inflammatory bowel disease
• Diverticular disease
• Intestinal Neoplasm or polyp
• Excessive ingestion of laxatives
• Viral gastroenteritis
• Bacterial infection
• Giardiasis
• Gastrinoma

• Complications
  • Osteopenia
  • Osteoporosis
  • Malnutrition
  • Weight loss
  • Rickets
  • Growth failure