Title: Adverse Reactions to Milk

Key words: Intolerance, allergy, immunological, anaphylaxis, galactosaemia, hypolactasia, lactose, lactase

Date: May 2000

Category: 8. The Gut

Type: Article

Author: Dr van Rhijn

Adverse Reactions To Milk

The Various Mechanisms Involved



Milk intolerance has been reported in 2.5% of the general child population1. It may be secondary to numerous biological mechanisms. Milk intolerance is defined as an unequivocal adverse, non-psychological reaction to milk, reproducible by challenge2. Some adverse reactions are due to milk allergy, which has many symptoms in common.


Immunologically-Mediated Allergy

Milk protein (b -lactoglobulin, casein, a -lactalbumin) allergy is a heterogenous3 group of disorders with multiple symptomatology, ranging from dermatological, gastrointestinal, respiratory conditions to stridor and anaphylaxis4, especially if it persists beyond the age of 6 years5. It is expressed via an IgE6, IgG4 or cell mediated allergy7 and affects 2.8 % of children during infancy8, with tolerance at three years for the majority. Human breast milk appears protective9, especially if mothers excluded milk during lactation10. Poorly understood mechanisms may be involved: family history of atopy, enhanced absorption of antigenic quantities of lactoglobulin in infancy, transient IgA deficiency or follow gastritis. Jejunal biopsy may reveal villous flattening.

Enzyme Deficiencies

Lactase, produced in the jejunal brush-border11 is required to metabolise lactose (disaccharide of glucose & galactose), into monosaccharides prior to absorption.

Congenital Lactase Deficiency (autosomal recessive [1:40,000]), causes neonatal diarrhoea on breast or lactose-containing feeding, leading to dehydration, acidosis and failure to thrive. Galactosaemia, diagnosed in the first week of life, is an enzyme deficiency disabling the conversion of galactose to glucose, with the consequence of jaundice, cataracts and mental retardation. A lactose-free diet is essential in these conditions. Cystic fibrosis and monoamine-oxidase inhibitors also cause enzyme deficiency and milk intolerance.

Selective Adult-type Hypolactasia results in lactose intolerance due to bacterial fermentation12 of lactose in the colon, causing flatulence, bloating, colic and diarrhoea13. It is highly prevalent in Eastern and African populations. The amount and form of lactose14 taken, along with gut transit time, determine how much lactose eventually enters the colon for fermentation and may contribute to oesphagitis, enteropathies, irritable bowel syndrome15 and atopic sensitisation16.


Secondary Hypolactasia due to damaged jejunal mucosa following enteropathies, infection or drugs can result in maldigestion. This is usually self-limiting after causal treatment. Diagnosed by jejunal biopsy, assay of disaccharidase activity or a positive hydrogen breath test.

Other Reactions

Severe Familial Lactose Intolerance is a rare hereditary condition with normal lactase activity, causing vomiting, lactosuria and aminoaciduria due to blood intoxication following gastric lactose absorption. Approximately 1:100,000 individuals may develop Pulmonary Infiltration (Haemosiderosis). Psychological stress17 and cultural attitudes18 may mimic lactose intolerance symptoms. Beta-casomorphine & other peptides cause an opiate effect when crossing the blood brain barrier and may contribute to autism.


It is imperative to confirm the symptom associations with milk intolerance with double blind challenge studies. The ‘gold standard’, oral provocation is the only reliable diagnostic test available19. Although most individuals can tolerate a certain amount of lactose20, anaphylactic reactions do occur and food should therefor be clearly labelled21. Pathogenesis, immunological mechanisms and sensitisation mechanisms are all poorly understood.




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