Lactose intolerance is a digestive condition in which lactose, the natural sugar in milk and many dairy products, is not fully digested. It usually happens because the small intestine has low levels of lactase, the enzyme that breaks lactose down.
Undigested lactose passes into the colon, where bacteria ferment it. This can produce gas and draw fluid into the bowel, causing symptoms such as bloating, wind, abdominal pain, and diarrhoea.
Symptoms
Symptoms often begin within a few hours of eating or drinking lactose. They can include:
- Bloating.
- Wind.
- Stomach cramps or abdominal pain.
- Diarrhoea.
- Nausea.
- Rumbling or discomfort after dairy.
The amount of lactose needed to cause symptoms varies. Some people tolerate small amounts, especially with meals, while others need stricter limits.
Causes
Common causes include:
- Lactase non-persistence, where lactase production falls after childhood.
- Secondary lactose intolerance, caused by small bowel injury or illness such as gastroenteritis, coeliac disease, Crohn's disease, or some treatments.
- Premature birth, where lactase production may be temporarily low.
- Congenital lactase deficiency, a very rare inherited condition present from birth.
Lactose intolerance is different from milk allergy. Milk allergy is an immune reaction to milk proteins and can be dangerous. Lactose intolerance is about digesting milk sugar and is mainly a gut problem.
Diagnosis
Diagnosis can be based on symptoms and response to reducing lactose, but testing may be used when the cause is unclear. Tests include hydrogen breath testing, lactose tolerance testing, and stool acidity testing in some children.
Other conditions can look similar, including irritable bowel syndrome, coeliac disease, inflammatory bowel disease, infection, and milk allergy. That is why persistent or severe symptoms should not automatically be blamed on lactose.
Management
Management is usually dietary. Many people reduce lactose rather than remove all dairy. Options include:
- Smaller portions of milk or dairy.
- Lactose-free milk and dairy products.
- Hard cheeses or yoghurt if tolerated.
- Lactase enzyme products.
- Fortified plant drinks where dairy intake is low.
- Attention to calcium, iodine, protein, and vitamin D intake.
NHS and NIDDK guidance both note that many people with lactose intolerance can still tolerate some lactose. The right amount depends on the person.
See Also
References
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