Lactose Intolerance in Children

Lactose intolerance in children is the occurrence of clinical symptoms (abdominal pain, bloating, flatulence, diarrhoea, nausea) that follow ingestion of lactose due to lactase deficiency (reduced lactase enzyme activity), distinct from cow's milk protein allergy.

• Types:
  • Primary lactase non-persistence (adult type hypolactasia): genetically programmed decline in lactase activity after weaning, usually clinically evident from age 4 to 5 years (earlier, from 2 to 3 years, in African, Asian and Native American children). Prevalence of lactase non-persistence is about 65 to 75 percent globally and up to 90 percent in East Asian and some African populations.
  • Secondary lactase deficiency: temporary injury to small bowel mucosa (acute gastroenteritis especially rotavirus, giardiasis, coeliac disease, Crohn disease, cow's milk protein enteropathy, malnutrition, chemotherapy, antibiotics); resolves in 2 to 8 weeks as mucosa recovers.
  • Congenital lactase deficiency: very rare autosomal recessive disorder with profuse watery diarrhoea from the first breast or formula feed; dehydration and failure to thrive.
  • Developmental lactase deficiency in premature infants (transient).
• True lactose intolerance in infants under 2 years is uncommon (except congenital and secondary after gastroenteritis); infant colic and regurgitation are rarely due to lactose.

• Symptoms 30 minutes to 2 hours after lactose ingestion: abdominal cramps, bloating, borborygmi, flatulence, loose or watery frothy stools, nausea, occasionally vomiting, perianal soreness (acidic stool); symptoms relieved by avoiding dairy.
• Dose related: most children tolerate small amounts (up to about 250 mL of milk spread out, or 6 to 12 g lactose daily).
• Examination normal; normal growth in primary lactase non-persistence.
• Red flags: faltering growth, bloody stool, fever, nocturnal diarrhoea, vomiting, severe pain, onset in the first weeks of life (congenital), anaemia, family history of coeliac disease or inflammatory bowel disease, symptoms to non-dairy foods, eczema or urticaria with milk (allergy), perianal disease, oral ulcers.

• Clinical: symptom diary, 2 to 4 weeks of lactose elimination with symptom resolution, followed by rechallenge with symptom recurrence.
• Hydrogen (and methane) breath test: 2 g/kg lactose (maximum 25 g) in water after an overnight fast; breath samples at baseline and every 30 minutes for 3 hours; rise in hydrogen of 20 ppm or more above baseline is positive. Avoid antibiotics for 4 weeks and laxatives for 1 week before.
• Stool pH below 5.5 and positive reducing substances (acidic stool in infants) support carbohydrate malabsorption.
• Lactose tolerance test (blood glucose rise under 1.1 mmol/L after 2 g/kg lactose) or genetic testing for LCT 13910 C/T variant (CC genotype in European populations); intestinal biopsy lactase assay rarely.
• Exclude: cow's milk protein allergy (IgE tests or supervised elimination and challenge), coeliac disease (tissue transglutaminase IgA), giardiasis, inflammatory bowel disease, irritable bowel syndrome, functional abdominal pain, toddler diarrhoea, infection.

• Reduce, rather than eliminate, lactose to a tolerated level for each child; most can take up to about 6 to 12 g lactose per sitting (equivalent to about 125 to 250 mL milk) especially with meals.
• Low lactose choices: lactose free milk, hard cheeses (cheddar, parmesan), yoghurt with live cultures, butter, fermented dairy; fortified plant based milks (soy, oat) with calcium for older children.
• Hidden lactose: bread, biscuits, processed meats, sauces, cakes, medicines; read labels.
• Lactase enzyme supplements (tilactase, beta galactosidase): about 3000 to 9000 FCC units orally just before or with dairy containing meals; drops can be added to milk for older children; evidence is modest.
• Calcium and vitamin D: ensure total calcium 700 mg (1 to 3 years), 1000 mg (4 to 8 years), 1300 mg (9 to 18 years) daily from low lactose dairy, fortified foods, canned fish with bones, tofu, green leafy vegetables, with supplements if needed (calcium carbonate 250 to 500 mg with meals); vitamin D 400 to 600 IU daily.
• Infants: congenital lactase deficiency needs lactose free formula from birth; secondary lactase deficiency after gastroenteritis: continue breastfeeding and normal formula; a short course (2 to 4 weeks) of lactose free formula only for persistent diarrhoea beyond 7 to 14 days; then reintroduce.
• Treat secondary causes: gluten free diet for coeliac disease; metronidazole 15 to 20 mg/kg/day (maximum 400 mg) orally in three divided doses for 5 days for giardiasis (or tinidazole 50 mg/kg single dose, maximum 2 g).
• Follow up at 4 to 6 weeks; re-challenge with lactose after secondary causes resolve; refer if poor growth or red flags.