Childhood food allergy - paediatric medicine

Many children outgrow allergies by school age, while studies have shown that breastfeeding may offer some protection against allergy, writes Dr Frankie Phillips.

Food allergy can cause eczema (above), asthma and rhinitis (Photograph: SPL)

The number of children being diagnosed with food allergy and using adrenaline autoinjectors is increasing. However, whether this reflects an actual increase in prevalence is not certain.

There remains a disparity between perceived and actual allergy. It has been estimated that the prevalence of adverse reactions to foods is up to 8% in infants and young children in the UK.1

Conversely, a recent study in Denmark showed that prevalence of allergy as reported by parents was 15%, whereas oral allergen challenge showed it to be 2.3% in children aged under three years and 1% in older children.2

It is thought that many children outgrow the condition before reaching school age. Current opinion on this matter varies. Some clinicians claim that 85% will have outgrown cow's milk protein allergy by three years of age, while others say this is closer to 20% by four years.3

However, other allergies, particularly peanut allergy, are severe and may be lifelong. It is unclear why some food allergies disappear after a few years and others are present for life and it is advisable to review the condition with oral rechallenge of the food allergen.4

What is a food allergy?
A true food allergy is an inappropriate action of the body's immune system against a protein within food. The resultant chain of events leads to the release of histamine, causing symptoms of eczema, asthma, rhinitis and, most severely, anaphylaxis. Anaphylaxis is severe and the whole body is affected, usually within minutes of exposure to the allergen, but sometimes hours later.

The severity of food allergy varies considerably, with anaphylaxis at the extreme end of the allergic spectrum. The release is triggered by the reaction between allergic antibodies (IgE) and the allergen. The immune system is involved, so clear diagnostic tests, such as IgE blood tests and skin prick tests, may be used, in conjunction with clinical history, to diagnose food allergy.

Food intolerance does not involve the immune system and is rarely life-threatening. The adverse reaction experienced may be hours or even days after the food has been ingested.

Intolerance may result from an inability to digest a food properly, for example, through lack of an enzyme such as lactose. Small amounts of a food may be tolerated, with symptoms only appearing when larger amounts are consumed.

Common food allergens
According to the British Dietetic Association, eight food allergens are responsible for about 90% of all allergic reactions (see box below). Other foods that might cause an allergic reaction (and must be included on food labels by law) are mustard, celery, lupin, sesame seeds and sulphites.

Common food allergens in childhood
  • Cow's milk
  • Eggs
  • Shellfish (including molluscs)
  • Fish
  • Soya
  • Peanuts
  • Wheat (and other gluten-containing cereals)
  • Tree nuts

The first food allergies to present in childhood reflect the first foods to be introduced to the diet; often cow's milk protein allergy, which affects 2-7.5% of children. Symptoms range from colic to atopic dermatitis and anaphylaxis.

Advice regarding weaning suggests that foods which might trigger the development of allergy should not be introduced before the age of six months. These foods should be introduced into an infant's diet one at a time, so that any allergic reaction can easily be identified.

However, evidence from a recent review concluded that either exposure to, or avoidance of, allergenic foods in early childhood provides no protection from subsequent development of food allergy.5 Furthermore, studies have shown that breastfeeding may offer some protection against allergy.

Peanut allergy is the most common severe allergic reaction to food. In summary, current advice, based on a review of the evidence from human studies,5 states that pregnant and breastfeeding women can continue to eat peanut products unless they themselves are allergic; that peanuts and other nuts should not be given before six months of age; and if a child has a known allergy or there is history in the immediate family, peanuts may still be introduced but parents are advised to discuss this with their GP or health visitor before giving them for the first time.

Managing food allergy
The mainstay of care is referral to a specialist allergy clinic where a detailed history and examination, as well as skin prick testing and specific IgE testing, will take place. The diagnosis is often confirmed by an oral challenge in a controlled hospital setting, but in some circumstances, such challenges are not advised.

It is important to establish a correct diagnosis. Emergency medication - antihistamines and adrenaline - is usually provided. Parents of a child who has recently had a life-threatening allergic reaction to food will understandably be anxious and an adrenaline autoinjector may reduce this. Parents should have clear instructions about how and when to give adrenaline.

Unfortunately, there are few predictors of the severity of a reaction; the type, amount of allergen, total IgE values and severity of a previous reaction are not indicative of the degree of risk. However, research has shown that asthma is consistently associated with severe reactions6 - consequently, the absence of asthma could be a reassurance.

Education of parents, children and teachers is a major part of management, to ensure allergen avoidance. The condition should be reviewed regularly and oral rechallenge may be appropriate. Organisations such as the Anaphylaxis Campaign (www.anaphylaxis.org.uk) and Allergy UK (www.allergyuk.org) provide much needed support for families.

  • Dr Phillips is a an independent registered dietitian in Devon

References
1. Venter C, Pereira B, Voigt K et al. Prevalence and cumulative incidence of food hypersensitivity in the first 3 years of life. Allergy 2008; 63: 354-9.

2. Osterballe M, Hansen TK, Mortz CG et al. The prevalence of food hypersensitivity in an unselected population of children and adults. Pediatr Allergy Immunol 2005; 16: 567-73.

3. Skripak JM, Matsui EC, Mudd K et al. The natural history of IgE-mediated cow's milk allergy. J Allergy Clin Immunol 2007; 120: 1172-7.

4. Colver AF, Nevantaus H, Macdougall CF et al. Severe food-allergic reactions in children across the UK and Ireland, 1998-2000. Acta Paediatr 2005; 94: 689-95.

5. Thompson RL, Miles LM, Lunn J et al. Peanut sensitisation and allergy: influence of early life exposure to peanuts. Br J Nutr 2010; 103: 1278-86.

6. Roberts G, Lack G. Food allergy and asthma - what is the link? Paediatr Respir Rev 2003; 4: 205-12.

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