Overview
Lactose intolerance is the inability to fully digest lactose, the main sugar in milk and dairy products, because of insufficient lactase enzyme production in the small intestine. Undigested lactose ferments in the colon, causing gut symptoms. It is different from a milk allergy, which is an immune response. Symptoms are manageable with dietary adjustments.
How common is it?
Lactase deficiency affects around 65 to 70% of the world's adult population. In northern Europe and among people of northern European descent, tolerance is higher (only 5 to 15% affected) due to lactase persistence gene. In East Asia, West Africa, and among many Indigenous populations, up to 90% of adults have lactose intolerance.
Causes and risk factors
Lactase enzyme production declines after weaning in most of the world's population (primary lactase deficiency). Secondary lactase deficiency follows intestinal disease.
Common risk factors
- Primary lactase deficiency: genetically determined decline in lactase after childhood (most common globally)
- Secondary lactase deficiency: gut infection (gastroenteritis), coeliac disease, Crohn's disease, chemotherapy
- Rare congenital lactase deficiency (present from birth)
Symptoms
- Bloating and abdominal distension
- Flatulence and wind
- Diarrhoea
- Abdominal cramping and pain
- Nausea
- Symptoms usually begin 30 minutes to 2 hours after consuming lactose-containing food
When to see a doctor
See a doctor if symptoms are new (especially over age 50), severe, or associated with blood in stool or weight loss. Coeliac disease and IBD can mimic lactose intolerance and must be excluded with appropriate tests before assuming the diagnosis.
Diagnosis
Hydrogen breath test after lactose load (gold standard non-invasive test). Lactose tolerance blood test. Small bowel biopsy shows reduced lactase activity. Dietary elimination and reintroduction trial.
Treatments
Dietary modification
Reducing or eliminating dairy products resolves symptoms. Many people tolerate small amounts of lactose spread throughout the day. Hard cheeses and yoghurt contain less lactose than milk.
Lactase enzyme supplements
Lactase tablets or drops (e.g. Lactaid) taken with dairy-containing food allow lactose to be digested normally. Available without prescription.
Lactose-free dairy products
Lactose-free milk, cheese, and yoghurt are widely available and nutritionally equivalent to standard dairy. Suitable for full dietary substitution.
Calcium supplementation
If dairy is significantly restricted, calcium intake must be maintained from non-dairy sources (fortified plant milks, calcium-set tofu, sardines, leafy greens) or supplemented.
Self-care and lifestyle
- Start with small amounts of dairy and gradually increase to find individual tolerance threshold
- Consume dairy with other food rather than on an empty stomach to slow gastric emptying
- Fermented dairy (yoghurt with live cultures) is often tolerated as bacteria pre-digest some lactose
- Ensure adequate calcium from alternative sources if avoiding dairy
Prevention
Lactose intolerance cannot be prevented. Secondary lactase deficiency may resolve if the underlying gut condition (e.g. coeliac disease) is treated.