Feature

Milk Allergy and Lactose Intolerance

Dr Harris Steinman

Lactose intolerance and allergies may be more prevalent than you think: "Among those over the age of five, approximately 90-95% of black individuals and 20-25% of white individuals throughout the world will have a partial or complete lactose intolerance."

There is a great deal of confusion between milk allergy and lactose intolerance, both adverse reactions attributable to milk. This article discusses the importance of both these conditions, their differences and what to do if you suffer from either condition

What is milk?

When we discuss milk allergy and lactose intolerance, we are referring to cow's milk. There are other types of milk available in the marketplace-
goat's milk, soy milk, etc.-and these are not comparable. For example, soy milk does not result in lactose intolerance.

Milk comprises water, protein, carbohydrates (a milk sugar called lactose), minerals, fats and a variety of other substances. There are over 30 different proteins in milk, and these are broadly categorised as members of the casein or whey group of proteins. When milk ferments, naturally or aided by chemicals in the dairy, the milk changes into a solid fraction (curd) and a watery fraction (whey). The solid fraction contains the proteins belonging to the casein group, in which there are 4 main proteins. The liquid portion contains most of the other proteins, and these belong mainly to the whey group of proteins.

What types of adverse reactions are possible?

Adverse reactions can be allergic (in this case, milk allergy), intolerance-based (in this case, lactose intolerance), or due to constituents that are less a matter of individual sensitivity.

Different mechanisms cause different adverse reactions. The resulting symptoms may be quite different from or confusingly similar to each other. The human body is able to mount a variety of defense mechanisms against proteins it regards as foreign or harmful. Scientists do not clearly understand why food proteins are regarded as harmful by the body, or how adverse affects occur. For example, some milk-sensitive individuals produce IgE antibodies to milk proteins, but some develop a milk protein "intolerance," which results from the body mounting a non-IgE immune response to milk protein.

A. Milk allergy

What is milk allergy?

Milk allergy refers specifically to adverse reactions involving immunoglobulin E (IgE) antibodies to one or more protein fractions of milk, whether belonging to the casein or whey protein group. Proteins belonging to the casein group are heat-stable, i.e., they cannot be broken down using heat. Thus, individuals allergic to casein proteins cannot tolerate any cow's milk, including boiled milk. In most instances, whey proteins can be broken down by heat.

The majority of IgE-mediated reactions to milk involve both the casein and whey fractions, which means that most milk-allergic individuals cannot tolerate boiled milk. Allergy to milk may occur in any individual. The group of people most commonly affected by milk allergy are young children, although people can develop milk allergy at any age.

How common is milk allergy?

Clinicians have not been able to determine the exact prevalence of allergy to milk. Studies throughout the world suggest that between 1% and 7% of children will develop allergy to milk. Allergy to milk in adults is much less frequent.

What are the symptoms of milk allergy?

Reactions can be immediate or start several hours or even days after the intake of moderate to large amounts of cow's milk. The most common symptoms are that of other food allergy: nausea, vomiting, diarrhoea and abdominal cramps, or symptoms involving the skin (urticaria [hives], eczema). See Table 1.

Three patterns have been recognised:

Type 1 - Symptoms start within minutes after the intake of small volumes of cow's milk. The reactions seen are mainly on the skin: eczema or urticaria (hives), with or without respiratory or gastro-intestinal symptoms.

Type 2 - Symptoms start several hours after intake of modest volumes of cow's milk. These symptoms are mainly vomiting and diarrhoea.

Type 3 - Symptoms develop after more than 20 hours, or even days after intake of large volumes of cow's milk. The main symptom is diarrhoea, with or without respiratory or skin reactions.

Colic in some children may be due to milk allergy. There is evidence that milk allergy in certain children may result in recurrent or chronic "glue" ear. Occult blood loss associated with cow's milk allergy can be a cause of iron deficiency (anaemia) in children.

Unfortunately, 50% of cow's milk allergy patients will develop an allergy to other food proteins (e.g., egg, soya, peanut), and 50-80% will develop an allergy to one or more inhalant allergens (e.g., grass pollens, house dust mite, cat) before puberty.

How is milk allergy diagnosed?

The diagnosis of milk allergy in infants may be easy if the symptoms started soon after the child began on milk formula (made from modified cow's milk). The diagnosis may also be easy if a person has the same reaction repeatedly after eating milk-containing food. In older children and adults, more often the diagnosis is difficult because milk is usually consumed with other food. Diagnosis usually entails clinical evaluation (medical history, family history, food history) supported by appropriate laboratory tests (CAP® RAST blood tests, skin-prick testing). An elimination-challenge test may be employed to make the diagnosis. Only the milk reactions that develop after a few minutes are very likely to give a positive blood or skin test, as these detect IgE that is involved in the immediate-type reaction. Approximately 30% of reactions are allergic in nature but not IgE-mediated. These may be difficult to diagnose using laboratory tests.

How is milk allergy treated?

Medication is ineffective in treating this condition. Avoidance of milk and milk-containing foods is the only treatment. (See Table 2.) This may be difficult to maintain, particularly as milk protein may be "hidden" in other foods. Soy milk may be substituted for cow's milk or cow's milk-derived formulae. Unfortunately, around 20% of milk-allergic children are also allergic to soy milk. A dietician must supervise treatment. Goat's milk is not a good alternative, as it contains a protein similar to one of the major ones in cow's milk. Milk may be present where least expected. For example, in vienna sausages, other sausages, fish fingers, pie crusts, crackers such as Provita, and breakfast cereals.

Prognosis

The majority of young children with milk allergy will outgrow it after avoiding milk for 12-18 months. Individuals who develop the allergy later in life will probably retain it.

B. Milk Intolerance

What is milk intolerance?

Lactose intolerance is a disease mainly of individuals over the age of five. Milk intolerance occurs as a result of the decrease or absence of an enzyme, called lactase, in the gastrointestinal tract that is required to metabolise the milk sugar lactose. The production of lactase is genetically programmed. Children are born with the lactase enzyme functioning correctly. At the age of around 5 years, for reasons unknown, black children partially or completely lose this enzyme. Children below the age of five who have a severe bout of diarrhoea or another severe illness may also develop temporary or permanent lactose intolerance. Because the level of lactase deficiency varies between individuals, some will be able to drink more milk before symptoms occur than others.

How common is Lactose Intolerance?

Among those over the age of five, approximately 90-95% of black individuals and 20-25% of white individuals throughout the world will have a partial or complete lactose intolerance.

What are the symptoms of lactose intolerance?

The common symptoms of lactose intolerance are nausea, vomiting, abdominal distension, abdominal cramps, and the passing of flatus (air). The degree of symptoms depends on the amount of milk taken in (more specifically, the amount of lactose) and the degree to which the body is deficient in lactase enzyme.

How is lactose intolerance diagnosed?

Doctors must consider both milk allergy and lactose intolerance when adverse reactions occur to milk.

There are no blood tests that can be used to support the diagnosis of lactose intolerance.

A stool sample can be tested by a laboratory for the presence of "reducing substances". This simple test indicates whether certain carbohydrates are present in the stool, thus indicating malabsorption of a sugar. The hydrogen breath test may also be used to diagnose lactose intolerance. In this test, the patient ingests a quantity of lactose and a breath sample is analysed for the presence of hydrogen. Hydrogen indicates that bacteria in the digestive tract have acted on undigested lactose and produced hydrogen as one of the metabolic by-products. Uncommonly, individuals may not be able to tolerate ordinary table sugar (sucrose), and this will also result in positive reducing substances or hydrogen breath tests.

Treatment of Lactose Intolerance.

Some individuals may be able to monitor their symptoms and learn to limit their intake of milk to their body's specific and individual limit. The majority of individuals will need to avoid all lactose-containing products. In infants and young children, calcium may need to be supplemented, as milk may be their only source of this mineral. Lactose-free milk is widely available overseas. Alternatively, a tablet is available that can be taken with a lactose-containing food to supply the required enzyme for breaking down lactose.

Products labelled as containing lactose, cream, butter, cheese and cheese flavour, curd, milk, milk solids, milk powder and whey, as well as margarine containing milk solids, should be avoided. (Some cheeses may be safe; a dietician should be consulted.) Products containing lactic acid, lactalbumin, lactate and casein do not contain lactose.

Prognosis

Lactose Intolerance is a life-long disease, unless it is a result of an acute severe illness, in which case the individual will recover lactase levels after a few months.

C. Other reactions

Certain antibiotics, e.g., penicillin, may be present in milk from a cow being treated for an infection. Individuals allergic to penicillin can thus be exposed to this antibiotic, resulting in a severe allergic reaction. Uncontrolled grazing by cows can result in the ingestion of certain weeds that contain a variety of chemicals, e.g., alkaloids, that may adulterate the milk. The training of dairy farmers and health regulations tend to protect consumers from these risks.

D. Conclusion

Adverse reactions to milk are not only allergy-related, but may also result from lactose sugar. Allergy adverse reactions may be mild to life-threatening, short-term to life-long. Intolerance adverse reactions are not life-threatening but may result in life-long discomfort. Secondary lactase deficiency is a consequence of inflammation in the digestive tract; thus, the intestinal inflammation caused by milk allergy sometimes results in lactase deficiency. Therefore, both milk allergy and lactose intolerance can exist concomitantly. A correct diagnosis must be made and properly followed up, as the treatment, dietary avoidance, is often very difficult and if incorrectly applied can lead to vitamin deficiencies or malnutrition.

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