Lactose Intolerance

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management

Definition

Lactose intolerance can be defined as the inability to digest lactose, a sugar found in milk and dairy products, due to a deficiency of the enzyme lactase in the small intestine.

Aetiology

  • Primary lactose intolerance: the most common type, results from a natural decline in lactase production after childhood.
  • Secondary lactose intolerance: this is caused by damage to the intestinal lining due to infections, coeliac disease, Crohn’s disease, or chemotherapy.
  • Congenital lactase deficiency: fairly rare genetic disorder where lactase is absent from birth.
  • Developmental lactose intolerance: often seen in preterm infants due to immature digestive systems.

Pathophysiology

  • Lactose is broken down by lactase into glucose and galactose for absorption.
  • In lactase deficiency, undigested lactose reaches the colon, where gut bacteria ferment it.
  • This produces gas (hydrogen, methane) and short-chain fatty acids, leading to bloating, diarrhoea, and abdominal discomfort.

Risk Factors

  • A family history of lactose intolerance.
  • In non caucasian ethnic groups (higher prevalence in African, Asian, and Hispanic populations).
  • Caused by GI infections (e.g., viral gastroenteritis).
  • Inflammatory bowel disease (IBD).
  • Coeliac disease.
  • Prematurity (immature lactase production).

Signs and Symptoms

Symptoms typically occur 30 minutes to 2 hours after consuming lactose containing foods:

  • Gastrointestinal symptoms:
    • Abdo bloating and cramping.
    • Flatulence (excess gas production).
    • Diarrhoea (osmotic, watery stools).
    • Nausea (less common).
  • Systemic symptoms (rare): fatigue, headaches.

Investigations

  • First line, dietary elimination test: there should be an improvement of symptoms with lactose avoidance confirms diagnosis.
  • Lactose tolerance test: monitors blood glucose levels after lactose ingestion (no rise suggests malabsorption).
  • Stool acidity test (in children): it detects lactic acid from undigested lactose.
  • Endoscopy with small bowel biopsy: used in suspected secondary lactose intolerance due to conditions like coeliac disease.

Management

1. Dietary Modifications:

  • Avoid lactose containing foods: such as milk, soft cheeses, cream, butter.
  • Lactose free alternatives: lactose free milk, plant based milks (soya, almond, oat).
  • Fermented dairy: some yoghurts and hard cheeses contain lower lactose levels.

2. Enzyme Replacement Therapy:

  • Lactase enzyme supplements: taken before consuming lactose-containing foods.

3. Nutritional Considerations:

  • Calcium and vitamin D intake: ensure adequate intake from alternative sources (e.g., green leafy vegetables, fortified foods).

4. Managing Secondary Lactose Intolerance:

  • Treat underlying condition (e.g., coeliac disease, IBD).
  • Lactose intolerance may resolve once intestinal health improves.
EndocrinologymypanotesLactose Intolerance