About Lactose Intolerance

Causes and Risk Factors

Genetics, age, ethnicity and damage to the small intestines are all risk factors for lactose intolerance.

Lactose intolerance can have several causes which affects the severity and progression of the condition. Lactose intolerance can be classified according to the following types: Primary, Secondary, Developmental/Transient and Congenital.

Primary Lactose Intolerance

Primary lactose intolerance is the most common type of lactose intolerance. It is estimated that primary lactose intolerance (or lactase deficiency) affects 60% of the world’s adult population.

Babies naturally produce lactase enzymes in response to the high concentration of lactose in breast milk. The production of lactase enzymes decreases as children are weaned. Although many people maintain sufficient production of lactase enzymes to digest the amount of dairy in a typical diet, for many their lactase production is insufficient for the amount of dairy they consume.

For some people, there is a significant reduction in lactase production as they age so that even trace amounts of dairy can cause digestive discomfort.

Primary lactose intolerance is genetic and is predominant in races where dairy has not traditionally been a staple part of the diet. For more information see Prevalence of Lactose Intolerance.

Secondary Lactose Intolerance

Secondary lactose intolerance occurs when the small intestine is damaged by illness, injury or surgery. As lactase enzymes are produced in the small intestine any damage can directly affect lactase production levels. Common causes of secondary lactose intolerance are:

  • Gastroenteritis
  • Persistent diarrhoea
  • Intestinal parasites
  • Giardiasis
  • Chemotherapy
  • Crohn’s disease
  • Inflammatory bowel disease
  • Coeliac disease

Treatment of the underlying disorder may restore lactase levels as the small intestines heal.

Developmental / Transient Lactose Intolerance

Developmental lactose intolerance (or transient lactose intolerance) may occur when a baby is born prematurely or is born with an immature digestive system.

Lactase production in the foetus develops late in pregnancy at 34 weeks gestation and is not completed until birth. Hence babies with a developmental age before full term will commonly suffer from lactose intolerance. As the baby’s digestive system matures the production of lactase enzymes increases, with sufficient production for normal digestion being reached by about 3-4 months of age.

Developmental lactose intolerance has been shown to be an important causative factor in many babies diagnosed with colic. Studies show approximately 40% of babies diagnosed with colic actually suffer developmental lactose Intolerance. Use of lactase supplements has been clinically proven to reduce crying time by at least 45% – from the first feed.

Congenital lactose intolerance

Congenital lactose intolerance, or Galactosemia, is a very rare genetic disorder that prevents any form of lactase production from birth.  Babies with congenital lactose intolerance show clear signs of malabsorption and dehydration, requiring immediate medical attention.


Risk FactorExplanation
AgeBabies: Premature babies and babies with immature digestive systems commonly show symptoms of lactose intolerance as production of lactase enzymes occurs late in pregnancy.
Studies show approximately 40% of babies diagnosed with colic actually suffer from transient lactose intolerance.
Elderly: We naturally produce less lactase enzymes as we age so the incidence of lactose intolerance increases with age. It is estimated that 60% of adults suffer some degree of lactose intolerance.
EthnicityPeople of Asian, Aboriginal, Indian, African and Mediterranean descent suffer a higher prevalence of lactose intolerance. Up to 75% of non-Caucasians living in Australia are lactose intolerant. Click here for more information about the prevalence of lactose intolerance across various ethnic groups.
Intestinal injurySmall Bowel Injury from gastroenteritis, persistent diarrhea, small bowel overgrowth, Giardiasis, chemotherapy or other injury to small intestinal mucosa can result in temporary lactose intolerance.
Intestinal disordersCoeliac disease, Crohn’s disease, inflammatory bowel disease & other intestinal disorders cause damage to the villi in the intestines where lactase is produced. Hence lactose intolerance is a common secondary effect of these conditions. The production of lactase enzymes resumes as the villi heal.

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