01.02.2007

A Peanut Hypothesis

Peanut allergies are one of the most frightening of all allergic reactions - especially when a young child is involved. Nutritional toxicologist Dr Peter Dingle throws some light on this troubling affliction of our times.


Peanutallergies are one of the most frightening of all allergicreactions - especially when a young child is involved.Nutritional toxicologist Dr Peter Dingle throws somelight on this troubling affliction of our times.

Food allergies, as well as many other atopic disorders,have been increasing in children over the past few decades.(1)While asthma has plateaued, eczema and food allergieskeep climbing.

ood allergies affect four to six per cent of childrenand three to four per cent of adults.(2) The most commonfood allergens in children include cow's milk, egg,soy, peanut, tree nut, shellfish, and fish.(3) Estimatesfor allergies to peanuts, other tree nuts or both arebetween 0.5 per cent (4) and one to two per cent (5).About three per cent of children have a positive peanutallergy test (such as a skin prick test), but only onethird of these will develop reactions upon eating peanuts.Australia has a relatively high prevalence of peanutallergy.

While the percentage of people with peanut allergiesis relatively low, the reactions are severe. They areone of the most dangerous forms of food allergy andthe number one cause of death from anaphylactic shock.(6)Each year in the United States, peanut allergies causeabout 30,000 anaphylactic reactions and 200 deaths.(7)Even the smallest amount of nut contamination, as lowas two milligrams of whole peanut, can have severe results.(8)

The allergies generally develop in early childhoodwith a median age of onset at 24 months.(9) Unlike manyother food allergies, it is less likely for an individualto develop a tolerance to peanuts; these allergies havelifelong reactions, becoming more severe with age.(10)In most children under five years of age with peanutallergy, the allergy will continue into later childhood.However, 20 per cent of children do grow out of theirpeanut allergy. Despite the gravity of the disease,there is very little known about the causes of peanutallergy. Underlying factors responsible for the increasein food allergies and atopic disorders may include bottlefeeding, early introduction of solid foods and imbalancein the immune system (T helper development in favourof Th2 over Th1 cells).(11)

What is peanut allergy?
Peanut allergies occur when the immune system mistakesa harmless substance such as a peanut for an infectiousone and begins to attack it. The immune system actsto release histamine into the blood and antibodies fromcells and organs to fight the perceived infection.

Peanut allergy symptoms characteristically occur quickly,within minutes of ingesting peanuts or peanut-contaminatedfood. Most allergic reactions to peanuts are mild andconsist of hives around the mouth where a peanut orpart of a peanut has touched the skin, or more generalisedhives on other parts of the body

Mild reactions include:(12) * Stomach ache * Runnynose * Itchy skin * Itchy, watery eyes * Rash and eczema* Urticaria * Tingling of lips and tongue More severesymptoms include:(13) * Laryngeal oedema * Asthma *Diarrhea * Vomiting * Angioedema (swelling of face andaround the eyes) * Anaphylaxis

Causes of peanut allergy
Little is known about the causes of peanut allergy,although children who have atopy, asthma, other foodallergies and a family history of peanut allergies areat a greater risk of having peanut allergies themselves.(14)

It has also been suggested that peanut allergies arelinked to soy milk and soy formula.(15) However, researchhas found no increase in the risk of the peanut-specificimmunoglobulin E antibodies or the peanut allergy duringthe first two years of life for children on a soy formula.(16)

Some researchers suggest a transfer of peanut allergythrough mother's breast milk, as peanut protein is foundin the breast milk of lactating women. However, thisdoes not appear to bring about the peanut sensitisation.Studies show the percentage of mothers who breastfedwas not associated with allergy to peanuts, and thatthe mothers of children with the allergy did not eatsignificantly more peanuts during breastfeeding thanmothers of children without the allergy.(17) The breastfeedingtheory does not explain why some children develop peanutallergy and others do not.

The increase in allergic disease seems to have somethingto do with our Western lifestyle because it happensin the West, and when people move from developing countriesto a First World environment they seem to get more allergies- including peanut allergies.

One hypothesis which has growing support is the "hygienehypothesis," also referred to as "exaggeratedhygiene." This suggests that little or no exposureto bacteria and viruses during a critical period ofinfancy can lead to an imbalance in the immune systemand result in diseases such as asthma, especially inhigh-risk groups, like children whose parents have asthma.Researchers theorise that when infants are exposed togerms early on, their immune systems are pushed to goin an "infection-fighting direction." Withoutthis push, the immune system's shift to infection fightingis delayed, and it becomes more likely to overreactto allergens - dust, mould, and other environmentalfactors such as food molecules that most people cantolerate.(18)

More likely it is the conditions that lead to gut dysbiosis- imbalances in the intestinal flora, such as the useof antibiotics by pregnant mothers and neonates andCaesarean births in particular - that contribute tothe increase in allergies, including peanut and otherfood allergies. We are, quite literally, too clean inside.

Gut function
The gut is a dynamic living organ in the body that isin constant contact and communication with its surroundingmedia. The mucous membrane absorbs and assimilates foodsand serves as a barrier to pathogens and other foreignchemicals and particles (antigens). Optimal functioningof the gut relies on good intestinal integrity. Whenthis integrity is compromised, the permeability of thegut may be altered; little gaps appear and gut functionerodes. Two major factors that determine the integrityof the gut are health of the gut lining (the mucosa)and a balanced bacterial population.

The human gut is the natural habitat for a large anddynamic bacterial community with more than one hundredtrillion bacteria and hundreds of different species.The biggest quantity - 30 to 50 per cent including over400 species - is in the large intestines, which affectits cell biology, structure and balance.

Major functions of the gut bacteria include: metabolicactivities that result in improved nutrition throughthe breakdown of food into usable energy; importantfeeding effects on the gut lining; immune structureand function; and protection of the colonised host againstinvasion by "alien" microbes. The gut bacteriaalso help manage gut physiology, particularly barrierintegrity. (19)

The gut lining (mucosa) is composed of close fitting,thin and semi-permeable (epithelial) cells separatedby tight junctures. When the intestinal mucosa (cellsincluding enterocytes and colonocytes) is disrupted,the permeability may increase, allowing larger particles,bacteria, undigested foods or toxins to cross the barrierinto the blood... causing an immune reaction and a subsequentfood allergy.

Unlike most other cells in the body which get theirenergy and nutrients from the blood supply, more than50 per cent of the energy needs of the small intestineand more than 80 per cent of the energy needs of thelarge intestine (where most of the bacteria are) comedirectly from the food in the gut. The preferred foodof these cells are short chain fatty acids like butyrate,acetate and propionate which are derived from the metabolismof indigestible carbohydrates in dietary fibre by beneficialgut bacteria, especially Bifidobacteria. The bacteriain the gut literally create the "food" forthe gut lining.

Any change in the relative proportions of the differentbacteria alters the subsequent nutrients available forthe digestive tract and its health. If the right foodis not available, the cells can literally get sick andstarve. Pathogenic bacteria or other micro organismsthat colonise the gut can also cause damage to the GImucosa by releasing toxins. Fortunately, the good gutbacteria help to keep the pathogenic bacteria in check.(20)

A Role for Probiotics
While probiotic (and prebiotic) therapy has been knownfor millennia, it has largely been disregarded by themedical world, until recently. There is currently arapidly growing appreciation for the role of the gutflora in health and disease. Overwhelming evidence hasaccumulated about the role of healthy gut bacteria inthe treatment and possible prevention of inflammatorybowel diseases,(21) Crohn's disease and ulcerative colitis,(22) including counteracting gut barrier dysfunction(23)associated with inflammation and infection.(24)

About 80 per cent of the body's immune system is localisedin the gastrointestinal tract. Experimental data andclinical studies have shown that the immune system ofinfants can be stimulated by the intestinal bacteria,with specific prebiotics and probiotics being shownto promote mucosal immunologic maturation in infants.(25),(26)The first months of life represent a critical periodfor the maturation of the infant's immune system and,thus, a window of opportunity for measures to improveimmune function and reduce the risk of disease.

Numerous recent studies including blinded placebo controlledstudies (the gold standard of clinical studies) havesupported these findings. In one study, infants at riskof developing atopy who received special probioticsduring the first six months of life, had a 50 per centreduction in atopic dermatitis after two years comparedto the control group. (27) The intake of probiotic-supplementedyoghurt reduced Japanese cedar pollinosis symptoms ininfants.(28) Administration of the probiotics at thetime of introduction of cow's milk in the infant's dietresulted in higher tolerance to cow's milk.(29) Theintake of probiotics showed a small reduction in thedays of illness, respiratory tract infections and gastrointestinaldisorders(30) and improved the response to Hib immunisationin six month old infants.(31) The beneficial effectof prebiotics (Oligosaccharides) has also been demonstratedin a high risk population of infants.(32)

A number of studies have now shown no adverse effectsassociated with probiotic use in infants as young asneonates, even in highly susceptible groups. (33)

The cause of the problem
Possible factors contributing to disruption of healthygut bacteria, gut dysbiosis and an increased risk ofdeveloping allergies, including peanut allergy, as aninfant include: * Antibiotics given to the mother orchild; * Caesarean birth; * Preservatives such as antimicrobials;and * Poor food such as dairy and wheat.
It is widely known that the use of broad spectrum antibioticshas negative effects on intestinal integrity and mayalter the balance between beneficial and pathogenicbacteria.(34) This is especially important in children,for whom antibiotics are prescribed frequently.(35)

This effect may be not only on a newborn receivingantibiotics, but also if the expecting mother receivesantibiotics. Colonisation of the infant's digestivetract occurs during the transition through the birthingcanal, and gut dysbiosis may remain for up to 12 monthsafter an initial disruption. Clinicians should thereforeconsider coadministration of probiotics with antibiotics.(36) Caesarean delivery alters the bacterial colonisationof the gut(37) for more than six months (38) which normallyoccurs shortly after birth and may have a protectiveeffect against the predisposition to asthma and allergies.(39)A number of large studies have shown that Caesareandelivery is associated with wheezing and allergic sensitisation.(40)

The gastrointestinal tract of a healthy foetus is sterile.During the birth process and rapidly thereafter, microbesfrom the mother and the surrounding environment colonisethe gastrointestinal tract until a dense, complex microfloradevelops.(41)

Diet is a major factor in maintaining a healthy humangastrointestinal tract. In infants who are breastfed,Bifidobacteria constitute about 90 per cent of theirintestinal bacteria. However, this number is lower inbottle-fed infants and when infants' diets are changedto cow's milk and solid food.(42) Foods with a highprebiotic potential such as vegetables, fruit and beans(legumes) will help maintain a healthy gut bacteriapopulation.

"Occam's razor" is a basic premise of scienceand suggests that the simplest solution is the mosteffective. Unfortunately, in today's pharmacology-dominatedmedical industry, this may not be the case. The additionof probiotics to infants and pregnant mothers is a simple,easy and a logical step now supported with a large amountof scientific evidence. And while colonisation in adultsappears to be only short-lived, it is stable for aslong as six months, and may persist for as long as 24months in infants.(43)

This approach is cheap, easy to implement and hasno negative side effects. The cost would be a mere fractionof the medical costs of one child who contracts a severenut allergy. The added benefit is that we already knowit will help in the reduction of other allergies suchas asthma and gut-related problems. For the children,this is a win-win approach to lifelong good health.

Peter Dingle is Associate Professor in Healthand the Environment at Murdoch University in Perth,Western Australia.

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