Lactase Deficiency

Lactase deficiency is reduced activity of brush border lactase phlorizin hydrolase (LCT) in the small intestine, resulting in impaired hydrolysis of lactose into glucose and galactose.

• Primary (adult type) lactase non-persistence: the commonest form. A genetically programmed decline in lactase activity after weaning, linked to polymorphisms upstream of the LCT gene (for example -13910 C/T). Prevalence is about 65 to 75 percent of the world's population; highest in East Asian, West African, and Native American populations (over 90 percent), and lowest in Northern Europeans (about 5 to 15 percent).
• Secondary lactase deficiency: temporary loss from mucosal injury (gastroenteritis, coeliac disease, Crohn disease, giardiasis, small bowel bacterial overgrowth, chemotherapy, radiation enteritis, tropical sprue).
• Congenital lactase deficiency: very rare autosomal recessive, with severe watery diarrhoea from the first feeds.
• Developmental lactase deficiency in premature infants.
• Lactase deficiency (enzyme level) is distinct from lactose intolerance (symptoms after lactose). Many people with lactase non-persistence tolerate up to 12 g lactose (about 250 mL milk) per sitting.
• Malabsorbed lactose is fermented by colonic bacteria to short chain fatty acids, hydrogen, carbon dioxide and methane, plus an osmotic load, producing symptoms.
• Prognosis: benign and manageable with diet; calcium and vitamin D intake needs attention.

• Bloating, flatulence, abdominal cramps, borborygmi, loose or watery stools, nausea occurring 30 minutes to 2 hours after lactose ingestion; severity relates to dose and to rate of gastric emptying.
• Perianal excoriation and acidic stool in infants.
• Red flags: weight loss, blood in stool, nocturnal symptoms, fever, anaemia, onset in infancy with failure to thrive, persistent vomiting, joint or skin manifestations (consider coeliac disease or Crohn disease).
• Examination: normal other than abdominal distension; check growth in children.

• Clinical: symptom diary with 2 weeks of lactose elimination and rechallenge.
• Hydrogen (and methane) breath test: after an overnight fast, 25 g lactose (50 g in some protocols) in 250 to 300 mL water; breath samples every 30 minutes for 3 hours; an increase in hydrogen of 20 ppm or more above baseline (or methane 12 ppm over baseline) is positive. Avoid antibiotics for 4 weeks and laxatives for 1 week before testing, avoid smoking and exercise on the morning, and fibre rich meals the preceding evening. Non-hydrogen producers (about 15 to 20 percent) may give false negatives.
• Lactose tolerance test: 50 g lactose, rise in blood glucose less than 1.1 mmol/L (20 mg/dL) at 60 minutes is abnormal.
• Genetic test for the LCT 13910 C/T variant (CC genotype is lactase non-persistent in European populations).
• Small bowel biopsy for lactase activity is rarely needed.
• Investigate secondary causes: coeliac serology, faecal calprotectin, stool microscopy, full blood count, if red flags or incomplete response to diet.

• Dietary lactose reduction not complete avoidance: most can tolerate up to 12 g lactose per sitting (equivalent to a 250 mL glass of milk); spread the intake throughout the day, take with other food to slow gastric emptying.
• Lower lactose foods: hard cheeses (cheddar, parmesan, under 0.1 g per 30 g), yoghurt with live cultures (bacterial lactase activity), butter, lactose free milk, fermented dairy.
• Hidden lactose: bread, biscuits, processed meats, sauces, medicines, and some tablets. Read labels.
• Lactase enzyme supplements (tilactase, beta galactosidase) 3000 to 9000 FCC units orally immediately before or with the first bite of a lactose containing meal; repeat with each meal; limited evidence of efficacy but safe.
• Calcium requirement: 700 to 1000 mg per day for adults (1000 to 1200 mg for postmenopausal women and men over 70); sources include fortified plant milks (calcium 120 mg per 100 mL), canned fish with bones, leafy greens, tofu set with calcium; calcium carbonate 500 mg orally twice daily with meals or calcium citrate if dietary intake inadequate. Vitamin D 800 to 1000 IU (20 to 25 micrograms) orally daily if low exposure to sunlight.
• Infants: congenital lactase deficiency requires lactose free formula from birth under paediatric specialist supervision. Secondary lactase deficiency in infants after gastroenteritis: continue breastfeeding; consider lactose free formula for 4 to 6 weeks only if prolonged diarrhoea.
• Treat the underlying cause in secondary deficiency (gluten free diet for coeliac disease; metronidazole 400 mg orally three times daily for 5 days for giardiasis; rifaximin 550 mg orally three times daily for 14 days or other regimen for bacterial overgrowth).
• Follow up at 4 to 6 weeks to titrate diet; re-introduce lactose after secondary causes resolve.