Lactose Intolerance

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Expert Reviewers
Dr John Wyeth, Gastroenterologist and Clinical Director of Medicine, Capital & Coast DHB
Dr Richard Steele, Clinical Immunologist and Immunopathologist, Wellington Hospital and Aotea Pathology
Dr Simon Chin, Paediatric Gastroenterologist, Starship Hospital

Key Points:

  • Most lactose intolerance is due to primary lactase deficiency which is genetically determined
  • Secondary lactase deficiency is transient and occurs mainly as a result of gastrointestinal illness
  • Lactose intolerance can normally be diagnosed through dietary challenge
  • Lactose intolerance is initially treated by minimising or avoiding lactose containing foods, however most people can tolerate one to two glasses of milk per day, in divided doses with food
  • People with primary lactose deficiency should be encouraged to gradually and regularly increase their intake of milk until a level of tolerance is achieved
  • Children who have developed secondary lactose intolerance as a result of infectious diarrhoea, may still safely receive milk

Background

Lactose intolerance is the clinical syndrome that occurs, when the inability to digest lactose results in gastrointestinal symptoms. It is estimated that around 70% of the world’s population are deficient in lactase.1 However not all lactase deficiency results in lactose intolerance and it is likely that its prevalence is over estimated.

Most lactase deficiency is genetically determined. In general, people of Northern European descent have lower rates of lactase deficiency (2–30%) and people of Mediterranean, South American, African and Asian descent have higher rates (60–100%).2,3 Both males and females are affected equally.4 There have been two studies in New Zealand, reported in the 1980s, which suggest that people of Māori and Pacific origin have a higher prevalence of lactase deficiency than New Zealand Europeans.5,6 A literature search did not reveal any recent follow-up studies to confirm these results.

Other physiological and psychological factors can contribute to gastrointestinal symptoms that mimic lactose intolerance.7 Many people may believe they are lactose intolerant, but do not actually have impaired lactose digestion.2

  • Lactose intolerance is NOT a milk allergy.
  • A milk allergy is related to the protein in milk rather than the lactose.2
  • Human breast milk contains 7% lactose and cow’s milk 4.8%.7
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