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Dairy Council Digest Archives
Dairy Food Sensitivity: Facts and Fallacies
Milk Protein Allergy
Cause. Cow's milk allergy is a reaction resulting from an abnormal immunologic response to one or more of cow's milk proteins (i.e., antigens or allergens). Although more than one immune mechanism may be involved in cow's milk allergy, immunoglobulin E (IgE) is the major class of antibodies produced (35). The involvement of the immune system distinguishes a food allergy from other food reactions. Although cow's milk contains more than 25 distinct proteins, the primary proteins responsible for milk allergy are B-lactoglobulin, casein, lactalbumin, and bovine serum albumin (36).
Prevalence. In contrast to lactose intolerance which is observed mainly in adults, milk protein allergy occurs primarily in infants and young children and rarely develops in adults (3,37,38). Furthermore, milk protein allergy rarely persists beyond three years of age (4,35,38). Immaturity of infants' digestive and immune processes and the fact that cow's milk proteins are the first foreign antigens encountered in large amounts likely contribute to infants' and young children's risk of developing milk protein allergy (37,38).
Although estimates vary, the prevalence of cow's milk protein allergy is about 1% to 3% (4,37–40). Children with a family history of allergies may be at higher risk of developing cow's milk protein allergy than those without this history (3,35,37,40).
Clinical Symptoms and Diagnosis. Cow's milk protein allergy can cause a broad spectrum of symptoms. These include gastrointestinal (e.g., vomiting, diarrhea, abdominal pain), cutaneous (e.g., atopic dermatitis or eczema, angioedema, urticaria or rashes), and respiratory (e.g., rhinitis, chronic cough, wheezing) symptoms (1,35,36,38,41). Anaphylactic shock is an extremely rare symptom of cow's milk protein allergy (6). Not only is there a broad spectrum of symptoms of varying severity, but their onset varies from about 45 minutes to more than 20 hours after consuming cow's milk protein (41).Based on their clinical and immunological types of reactions, patients can be classified into immediate or later onset reactors. Nearly all patients with cow's milk protein allergy have more than one symptom. Typically, symptoms of cow's milk protein allergy begin in the first year of life and coincide with the time of introduction of cow's milk based formula (35).
"Cow's milk protein allergy affects a relatively small percentage of infants and young children (1% to 3%) and is generally outgrown by three years of age."
A diagnosis of milk allergy cannot be made on the basis of symptoms alone (38). Researchers have demonstrated that less than one-half of infants with symptoms attributed to cow's milk allergy are confirmed by a cow milk challenge (4,42,43). An accurate diagnosis of cow's milk allergy is important to avoid adverse reactions and/or prevent the unnecessary elimination of cow's milk from the diet (38). Unfortunately, there is no single laboratory test on which to base a diagnosis of cow's milk protein allergy (35). A series of tests and information is used to diagnose this condition.
A thorough medical history (i.e., symptoms, time of reaction), complete physical examination, and selected laboratory tests can help exclude other potential causes of milk-induced symptoms such as lactose intolerance. The generally accepted procedure to identify cow's milk allergy is to remove cow's milk from the diet for 7 to 14 days to determine whether or not symptoms resolve (4). If symptoms disappear, cow's milk may be reintroduced, first in small amounts and then in increasing amounts, until symptoms result or milk is tolerated when consumed in usual amounts (4). To determine if the immune system is involved or to detect IgE antibodies to cow's milk protein, several tests such as prick skin tests and blood tests known as the radioallergosorbent test (RAST) or the enzyme-linked immunosorbent assay (ELISA) are available (2,43).
If the above tests indicate milk protein allergy and if reactions are not severe, a food challenge may be carried out. In a food challenge, cow's milk is given in increasing doses under medical supervision until the individual develops symptoms or tolerates a usual serving. The double-blind placebo-controlled food challenge test is considered to be the "gold standard" or most conclusive method to diagnose cow's milk protein allergy (35,38,44)
Management, Prognosis, and Prevention. Once a diagnosis of cow's milk allergy has been made, the only proven therapy is strict elimination of cow's milk from the diet (3,36,38). Management of cow's milk allergy should be aimed at relieving symptoms without compromising nutritional status or growth (45). Because elimination diets may result in nutritional shortcomings (46), these diets should be undertaken only with the advice of a physician and/or dietitian while closely monitoring children's growth and development (45,47).
"Determination of the cause of reactions to food and their management should be medically supervised to prevent serious reactions and nutritional deficiencies."
For infants and young children with cow's milk protein allergy, alternative milk sources include soy milk, or whey hydrolysate, casein hydrolysate, or amino acid hypoallergenic formulas (48). Although soy protein allergy is less common than cow's milk protein allergy, some children who experience adverse reactions to cow's milk protein experience similar reactions to soy protein (48,49). Most infants with cow's milk protein allergy tolerate hypoallergenic formulas, but none of these formulas are nonallergenic (1,50).
The prognosis for cow's milk protein allergy is excellent with most children outgrowing this condition by about three years of age (4,35,38). Because milk protein allergy tends to be a transient condition, cow's milk should be reintroduced under medically supervised challenged conditions every 6 to 12 months so that this food can be included in the diet as soon as possible.
While sensitization to cow's milk protein can occur prenatally and in breast-fed infants (2,35,51), there is no conclusive evidence that restricting intake of cow's milk during pregnancy or lactation prevents cow's milk protein allergy in infants (52–54). Moreover, cow's milk restriction potentially may compromise nutrient intake (55).
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