The allergy epidemic

About one in 10 New Zealand children has a food allergy. New research sheds light on ways to reduce the risk. Dietitian Anna Richards explains.

Allergies are on the rise worldwide, particularly in the western world. The word allergy tends to be thrown around too loosely, however. A simple intolerance or bad reaction to food can be dubbed an allergy when there is a whole range of other causes. A food allergy always involves the immune system, while most other food reactions and intolerances do not.

For example, reduced levels of enzymes such as lactase (which metabolise lactose or milk sugar) can lead to nausea, bloating and diarrhoea. For this reason, it is commonly assumed to be a food allergy, but as it doesn’t involve the immune system, it is an intolerance (lactose).

Largely unknown is that children ‘grow out of’ most food allergies. The public perception is that food allergies affect around 25 per cent of the adult population, but the real figure is estimated to be as low as 2-3 per cent.

While you can be allergic to just about any food, those usually responsible number less than 10 — milk, egg, soy, wheat, peanut, treenut (eg cashews, almonds, walnuts) fish and shellfish account for around 90 per cent of all food allergies.

Milk is the primary allergen in infants under 12 months, while the humble egg is the most significant in the second year of life. Fortunately, around 85 per cent of infants with allergies to milk and egg outgrow this during early school years. Nut statistics aren’t so good — only 20-30 per cent of children outgrow peanut allergy and 15-20 per cent treenut. Fish and shellfish allergies also tend to persist into adulthood and, along with nut, account for the top three allergies in adults.

Interesting also is that common allergens differ between countries. While milk, egg and nut tend to dominate in the western world, fish is significant in Scandinavia and lupin (a type of legume) is increasingly problematic in France.

Is there a genetic link?

The short answer is yes, there is. Atopy refers to a genetic tendency to allergy. Babies born into atopic families with eczema, asthma, hay fever and food allergy are more sensitive, especially if parents and siblings are also affected.

The role of the gut

Babies born by Caesarean section have a very different gut microbiota (micro-organisms) to those born naturally. Those born naturally have more lactobacillus and bifidobacteria — micro-organisms thought to be more protective against allergy. A mother or baby on antibiotics may further alter gut microbiota (see our feature Gut and mood: The surprising connections for more on gut health).

Breastfeeding is regarded as being uniquely protective against allergy as breast milk contains prebiotics that encourage the growth of ‘good’ gut microbiota. Exclusive breastfeeding to around six months is considered to be a great start in preventing allergy. The early introduction of formula seems to be a risk factor for milk allergy in susceptible babies.

New Zealand mothers start well with breastfeeding, but Plunket figures indicate these rates drop quickly with only 65 per cent of babies still fully breastfed at six weeks, 55 per cent at three months and 23 per cent at six months.

It has also been suggested that introducing potentially allergenic solids (while continuing breastfeeding) may be protective. While the delayed introduction of solids has long been thought to protect against food allergy, more and more evidence suggests this may be a factor in increasing the incidence of allergy.

New research on peanuts

Peanut allergies have increased significantly in the western world over the past 10 years and, remarkably, this has coincided with a delayed introduction of peanuts.

The LEAP (Learning Early About Peanut Allergy) study in the UK was initiated after identifying that Israeli children living in London had high rates of peanut allergy, while those in Israel had much lower rates, despite having the same genetics. The significant difference is in the environment — the early introduction of peanut in the form of Bamba (peanut butter-flavoured puffed maize) from a few months old in Israeli children, compared to the late introduction of peanut in the London-based children.

Results published this year showed 17 per cent of infants at high risk of allergy where peanut was excluded from the diet, went on to develop peanut allergy in contrast to only 3 per cent of infants who ate peanut at an early age.

Dual exposure hypothesis

This theory proposes that babies in homes where, for example, eggs are eaten and egg residue lingers on hands and clothes, and where the baby is genetically predisposed to allergy or has dry skin or eczema, are at increased risk of sensitisation even before they start eating eggs. Environmental exposure while consuming the food, on the other hand, seems to be protective.

This goes some way to explain this new research on peanuts where eating peanuts at the same time as skin exposure to them is thought to be protective, particularly in atopic babies or those with eczema.

The new message could be two-fold: the environment and when the allergen is introduced as food is more significant than we thought. Also, keeping babies’ skins well moisturised helps to form a stronger skin barrier against allergens.

Vitamin D

There is a higher incidence of allergy in babies born and breastfed over the winter months suggesting that vitamin D is a confounding factor for allergy. For this reason, supplementary vitamin D is recommended for pregnant women, particularly those pregnant during winter months, as well as those with darker skin or who have less outdoor time and exposure to the sun.

What might happen in an allergic reaction?

• Skin: Rash around the mouth, hives, eczema
• Angioedema: Swollen lips, eyes or mouth
• Anaphylaxis: Swollen tongue, difficulty breathing, wheezing, rapid drop in blood pressure and, in extreme cases, collapse
• Gut: Vomiting, diarrhoea, mucousy stools, blood in the stool, drop-off in growth

If you suspect your child has had an allergic reaction, consider

• Timing: An allergic reaction will be within two hours of consuming the food but may not necessarily be on the first exposure.
• Has the child eaten the food regularly before?

An allergic reaction to a food may occur on the first exposure, but may also occur after eating the food a couple of times.

It’s unusual to have an allergic reaction to a food that has been consumed with no previous reaction, hence, even if test results show an intolerance or sensitivity to a particular food, tolerance is key. So if no obvious reaction has taken place, it is probably more beneficial for immunity to carry on eating the food.

What to do?

If an allergic reaction is mild — a rash, for example — it’s reasonable to give some antihistamine and watch to see if it settles. If the symptoms are progressing, however, it’s sensible to err on the side of safety and have someone take you and baby to the hospital emergency department. Whenever the airway is involved, or if baby becomes pale or floppy, it’s recommended to call an ambulance.

What to test?

Suspect foods are worth testing for, but testing for everything is not particularly helpful as it can lead to more questions and anxiety than solutions. Medically recognised tests include skin prick tests or Specific IgE tests (previously known as RAST tests). Alternative tests such as hair testing and cytotoxic testing (cell reaction) are not as useful as they can be unreliable, restrictive and expensive.

However, neither the presence of food allergy nor its severity can be predicted by allergy tests alone. Results are best reviewed with your GP or allergy specialist.

Allergic reactions are unpredictable so every allergen exposure has to be regarded as potentially life threatening. Friends and family need to know, but because a child with food allergy is otherwise well, it can be hard for others to understand how quickly this can become a life-threatening situation.

Also, bear in mind that some allergens co-exist, so there is often caution around, for example, egg in a milk-allergic baby. If one treenut is a problem, there may be another one that causes a problem. If cow’s milk is a problem there is a 97 per cent chance that all mammal milks will be a problem.

More and more though, there is also an accepted view that if it ‘ain’t broke, don’t fix it’. No food should be excluded from a baby’s diet without good reason.

When to involve a specialist?

Anyone with multiple and/or severe food allergies is best under the care of a specialist allergist. This might not be possible in some parts of New Zealand.

Asthma also increases the risk of a life-threatening allergic reaction, so well-managed asthma is important, as is involving an asthma nurse.

When to involve an allergy dietitian?

Children and adults with allergies have a different relationship with food, which can lead to aversions and a ‘narrow’ diet. A specialist dietitian will ensure you or your child’s diet is nutritionally balanced and also be able to identify when tolerance is increasing.

For example, a growing tolerance for milk might include tolerating it in a well-cooked commercial biscuit first, then in a home-cooked muffin, then in something cooked on the stove such as a pikelet, then a small piece of cheese and finally a small serve of whole milk. Egg follows a similar process.

Risk factors for your baby developing food allergy

• Atopic family, particularly immediate family members with allergy
• Caesarean delivery
• Born and breastfed in the winter months
• Early introduction of formula
• Severe cradle cap
• Dry skin/early onset eczema
• Reflux that doesn’t respond to medication
• Poor growth
• Persistent diarrhoea, mucousy stools, blood in the stool

Allergy terms

• Allergen: A food protein that causes the immune system to overreact to it as a foreign invader
• Sensitised: When an allergy test shows positive, but the food has not yet been consumed
• Allergy: When you have consumed the food AND it has caused an allergic reaction
• Tolerance: When you consume the food without any problem, no matter what allergy tests say
• Resolving allergy or achieving tolerance: Becoming tolerant of a food is a gradual process over time. It is commonly tolerated in small quantities in a well-cooked form and on a step-by-step basis before it is tolerated as a whole food.

Allergy or Intolerance?