Lactose intolerance — milk sugar malabsorption
Lactose is disaccharide sugar in milk and dairy — requires lactase enzyme in small intestine to split into glucose + galactose for absorption.
Lactase non-persistence — genetically programmed decline after weaning — normal for most humans globally — ~65% world population.
Northern Europeans — lactase persistence mutation — dairy tolerance common.
Symptoms
After lactose load (dose-dependent):
Timing: 30 min – 2 hours — intestinal fermentation by bacteria
NOT:
- immediate urticaria — allergy
- weight loss, blood in stool — investigate other causes
Lactose intolerance vs milk allergy
| Lactose intolerance | Milk allergy | |
|---|---|---|
| Mechanism | Enzyme deficiency | IgE/non-IgE immune |
| Onset | Delayed | Minutes–hours |
| Anaphylaxis | No | Possible |
| Age | Teens/adults common | Infants common |
Milk allergy — separate condition — paediatric/allergy clinic.
Diagnosis
- Clinical history — relationship to dairy dose
- 2–4 week low lactose trial — symptoms improve
- Lactose challenge — symptoms return
- Hydrogen breath test — specialist
- Exclude coeliac — IgA TTG — see coeliac disease
Management
Reduce lactose dose
- trial tolerance level — may tolerate milk in tea not pint of milk
Lactose-free products
- Lactose-free milk — same calcium
- plant milks — check calcium fortified
Lactase supplements
- tablets with dairy meal
Usually tolerated
- hard cheese
- butter — minimal lactose
- probiotic yoghurt — individual trial
Nutrition if dairy limited
Calcium targets:
- 700mg/day adults — 1000mg pregnancy
Sources:
- fortified plant milk
- tinned fish with bones
- green leafy veg
- fortified bread
- supplements if inadequate
Vitamin D — see NHS guidance
Secondary lactose intolerance
Temporary after:
- gastroenteritis
- coeliac (until treated)
- IBD flare
Lactase returns when gut heals — retrial dairy later.
When to see GP
Red flags NOT lactose alone:
- nocturnal diarrhoea
- weight loss
- rectal bleeding
- anaemia
→ IBD, coeliac, cancer screen as indicated.
Lactose intolerance is annoying not dangerous — diagnosis prevents unnecessary dairy fear and ** ensures calcium** if intake drops.
Common questions about lactose intolerance
- What are the symptoms of lactose intolerance?
- Bloating, excessive wind, abdominal cramps, gurgling, diarrhoea or loose stools — typically 30 minutes to 2 hours after milk, ice cream, soft cheese, or large dairy portions. Severity depends on lactose dose and your enzyme level — small amounts in tea may be fine.
- What is the difference between lactose intolerance and milk allergy?
- Lactose intolerance — digestive enzyme deficiency — not immune — never causes anaphylaxis. Milk allergy — immune reaction to milk protein — can cause urticaria, vomiting, wheeze, anaphylaxis within minutes to 2 hours — more common in infants. Different tests and treatments.
- Can I still eat cheese if lactose intolerant?
- Often yes — aged hard cheeses (cheddar, parmesan) contain minimal lactose. Yoghurt with live cultures may be tolerated — bacteria partially digest lactose. Fresh milk, ice cream, and soft cheeses highest lactose — most problematic.
- How is lactose intolerance diagnosed?
- Clinical history often sufficient — trial off lactose then challenge. Hydrogen breath test after lactose drink — rises if malabsorption. Coeliac screen if symptoms overlap — untreated coeliac causes secondary lactose intolerance improving on gluten-free diet.
- Do lactase enzyme tablets work?
- Lactase supplements (Lactaid etc.) taken with dairy help many people digest lactose — effectiveness varies. Lactose-free milk has enzyme added — tastes slightly sweeter — good calcium source.
Sources
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