Notes for post 'Childhood allergies: What can parents do to prevent them?'

Dr Breanne Kunstler (BBiomedSci, BHealthSci, MPhysio, PhD).

Introduce specific allergens early, often and orally

Previously encouraged to avoid ingestion of food allergens, like egg/cow’s milk/peanut, has been rescinded because recent evidence does not support this method to avoid the development of food allergy. Instead, early exposure is encouraged.

Review: avoidance diets during pregnancy and lactation are not recommended to prevent food allergy. Exclusive breastfeeding for 4-6 months is encouraged, with complementary foods added from 4 months, to prevent food allergy

Review: tolerance to food allergens is promoted by oral exposure early in life. Conversely, exposure through the skin barrier can sensitise children to food allergies.

Review: convincing evidence for the early introduction of peanut to prevent peanut allergy, but convincing data doesn’t exist for other foods.

Review: egg exposure from 4 months associated with reduced egg allergy and sensitisation. Peanut exposure from 4 months compared to delayed exposure associated with reduced peanut allergy. Introducing solids before or after 4 months not associated with allergy but is associated with sensitisation.

Review: complementary foods, including common allergens, should be introduced between 4 and 6 months. Peanut should be introduced before 12 months in infants affected by severe eczema and or egg allergy (i.e. high-risk infants) to reduce chance of peanut allergy. However, should see your doctor first to ensure the testing process is as safe and effective as possible. Encouraged to introduce heated egg at 6-8/12 to reduce egg allergy.

Review: “A systematic review191 concluded that there was ‘‘moderate certainty’’ of evidence for reduced egg allergy with introduction at 4 to 6 months. Although there is currently no recommendation to purposefully feed egg early, there remain recommendations not to avoid including egg in the early infant diet.181,182 The above referenced egg studies186,188 noted high rates of reaction on raw egg introduction, raising questions of safety and the possibility that high-risk infants might already be allergic by 4 to 6 months”

Review: introduction of peanut and hen’s egg white in early infancy can prevent food allergy (RCTs). Commence at 4-6/12. More research needed for other allergens. Oral allergen exposure can support tolerance of common allergens. Conversely, allergenic sensitisation is promoted through cutaneous exposure.

Review: Unclear if timing of solid food introduction influences risk of developing eczema.

Review: delayed introduction to solids and to allergenic foods is not associated with decreased risk of developing allergenic disease in both high and low risk infants. Later introduction was associated with increased risk of allergy development.

Review: no evidence to avoid or encourage exposure to ‘highly allergenic’ food in the first 1000 days to modify allergy risk or develop tolerance to certain allergens.

Review: no association between early introduction of cow’s milk or cow’s milk formula and risk of asthma, wheeze, eczema or atopic dermatitis. Evidence is low quality.

When in Rome (and Australia), do as the Romans do: Eat (and feed) a Mediterranean diet

Review: Mediterranean diet consumed by pregnant mother in the first 1000 days associated with lower risk of allergenic sensitisation and allergic rhinitis (high fat, western diet with higher risk of respiratory distress syndrome at birth and higher risk of chronic lung disease later). Western diet in children 0-2 associated with higher risk of wheeze, asthma and hyperresponsiveness (lower risk for children following Mediterranean diet). Mediterranean diet also associated with lower risk of atopy, wheezing and asthma. Pregnant women not encouraged to avoid any foods to prevent allergy but following Mediterranean diet could be protective.

Review: children consuming Mediterranean diet can have a protective effect on asthma/wheeze. Pregnant mothers following Mediterranean diet had some protective effect for offspring on asthma/wheeze in the first year only. No significant effect seen in preventing eczema, rhinitis or atopy though.

Fruit and vegetable consumption appears to be protective against asthma

Review: current research insufficient to determine if pregnant women consuming a Mediterranean diet is truly protective for the child developing asthma and allergies. But it shows promise.

Review: child consuming a Mediterranean diet is associated with less chance of developing asthma by children >18 years.

Review: inconsistent evidence of any association between maternal diet in pregnancy and lactation and allergy and atopy outcomes in offspring.

Review: fish intake during pregnancy is not associated with lower risk of allergies in the infant. However, consumption of fish by the infant during the first year reduces eczema and allergenic rhinitis risk. (full text)

Review: first 1000 days exposure to vaccenic acid (a R-TFA (ruminant trans fatty acid)) might have a protective effect on eczema (inverse assoc seen, OR 0.42). Higher n6/n3 ratio and linoleic acid in first 1000 days associated with higher risk of eczema (only marginally, 1.06). No strong evidence found for PUFA or other R-TFA exposure in first 1000 days/early life can reduce chance of developing other allergenic diseases (eczema, asthma, wheeze and allergenic rhinitis) or sensitisation.

Review: No evidence to encourage PUFA, certain micronutrient or antioxidant intake in first 1000 days to reduce allergy risk.

Review: supplementation of long chain PUFAs during pregnancy led to reduce risk of the offspring become sensitise to egg and peanut. Nothing seen for eczema and asthma/wheeze. Small number of studies in this area though and aren’t of high quality.

Review: protective association between increased pre-natal n3 long chain PUFAs or fish intake and incidence of allergenic disease in child. Also, significant reduction in atopic eczema, sensitisation to egg and any food in the first 12 months of life for offspring of women consuming PUFAs/fish prenatally. However, evidence between studies remains inconsistent so can’t be confident in findings.

Review of reviews: negative association between asthma or wheeze and intake of fruits and following Mediterranean diet.

Protect your gut health

Review: probiotic supplementation during late pregnancy and breastfeeding might reduce eczema risk. Fish oil supplementation during pregnancy and breastfeeding may reduce risk of sensitisation to food allergens.

Review: probiotic administered prenatally to pregnant mother and postnatally to child can reduce atopy and risk of food hypersensitivity (this doesn’t mean it’s associated with no food allergy, as hypersensitivity is the stage before allergy) in young children. But they must occur together, administering either prenatally OR postnatally doesn’t have a relationship.

Review: for children already hypersensitive or allergic to certain foods, using probiotics can help reduce clinical symptoms and even modulate the immune system. More research is needed to determine how to best harvest the power of probiotics for this purpose.

Review: disturbed gut microbiota can increase risk of allergy. Changing microbiota using diet (e.g. fibre, prebiotics) in pregnancy may reduce allergenic airways disease and food allergy in offspring. Remains unclear which bacteria, what numbers and what combinations and when during the gut colonisation process may prevent allergenic disease and asthma.

Review: lower bacterial diversity in children is associated with developing allergenic disease.

Review: certain combinations of bacteria in the gut can increase the chance of allergenic sensitisation compared to other combinations. Reduced bacteria diversity can be associated with developing allergenic disease. Evidence is clearer in neonates compared to older children, especially for asthma, suggesting early life microbial exposure is more important than later when developing allergenic disease. Research in this area is young.

Review: it is unclear if supplementing infants with prebiotics can reduce the development of allergies.

Review: Dysbiosis can increase susceptibility to food allergy.

Review: having a diverse microbiota can support tolerance of common allergens. Conversely, allergenic sensitisation is promoted through reduced microbiota diversity.
Australian cohort study: "Analysis of the V4 region of the 16S rRNA gene in fecal samples shows maternal carriage of Prevotella copri during pregnancy strongly predicts the absence of food allergy in the offspring"

Get some sun

Review 1 and review 2: lack of evidence to suggest a link between prenatal vitamin intake and allergies. Some evidence that vit D consumption might reduce recurrent wheeze in children. But some literature either suggesting no relationship or a relationship between too high vit d or too low and allergies.

Review: protective effect of maternal intake of each vitamin D, vitamin E, and zinc in the first 1000 days against childhood wheeze. Inconclusive for effect on asthma and other atopic conditions.

Review: low maternal vitamin D status associated with higher childhood eczema risk. No relationship seen for asthma or wheeze.

Review: no association between vit D status of children and food allergy.

Review: insufficient evidence to suggest association between vit D supplementation antenatally and offspring wheeze/asthma as children and in later life.

Review: the more vitamin D children have in their blood, the less chance they have of being sensitised to allergens in the air (e.g. pollen) and having allergic rhinitis (seen mainly in adult men rather than women).

Review: Very low certainty in the body of evidence across examined studies suggests that vitamin D supplementation for pregnant women, breastfeeding women, and infants may not decrease the risk of developing allergic diseases such as atopic dermatitis (in pregnant women), allergic rhinitis (in pregnant women and infants), asthma and/or wheezing (in pregnant women, breastfeeding women, and infants), or food allergies (in pregnant women). 

Review: mothers’ consumption of Vit D during pregnancy is inversely associated with offspring developing respiratory tract infections. No associations were found between vit d and wheeze, asthma, atopic eczema, allergic rhinitis, and allergic sensitization.

Review: Compared to those who did not take vitamin D, the mothers who had vitamin D supplementation during pregnancy stage could reduce the risk of asthma or wheeze in infants. 

Review: in utero vit D deficiency might be protective against childhood LRTI. More research needed on childhood allergy and infection outcomes as either little evidence out there to show if there’s an association or not, or the results are inconsistent.

Population study: Folate intake and folic acid and vitamin D supplement use were associated with an increased risk of cow’s milk allergy in the offspring, whereas vitamin D intake from foods during pregnancy was associated with a decreased risk of cow’s milk allergy.

Review of reviews: negative association between asthma or wheeze (not restricted to age group) and dietary intake of vit C, E and D

Review: Sufficient levels of vitamin D can support tolerance of common allergens. Conversely, allergenic sensitisation is promoted through vitamin d deficiency.

Breastfeed as much as is possible, but not to reduce allergy risk

Review: breastfeeding in the first 1000 days has beneficial effects on respiratory infections but evidence about protective effect on allergic disorders is unclear.

Review: never consuming breastmilk is associated with higher risk of childhood asthma, so is shorter duration of breastfeeding compared to longer duration. Evidence specific to the association between human milk consumption and food allergy, allergic rhinitis and atopic dermatitis is limited.

Review: No strong evidence to support human milk (HM) transforming growth factor beta (TGF‐β) consumed through breastmilk being associated with development of allergies in children.

Review: remains unclear how components of breast milk, like immunoglobulins, affect infant microbiota and eczema risk. Suspected that breastfeeding has a protective effect for the child when it comes to developing several allergic diseases.

Review: limited evidence saying that low concentrations of certain sugars (LNFP-II) in breastmilk are associated with cow’s milk allergy and higher fucosyloligosaccharide level protect infants from infectious disease.

Review: association between exclusive and nonexclusive breastfeeding and asthma are mixed. No clear picture for eczema and allergic rhinitis either.

Review: unclear if fatty acids (PUFAs, specifically), found in colostrum and breastmilk are associated with less allergenic disease for the infant.

Review: tolerance to food allergens is promoted by transfer of immune complexes specific to the allergen through breast milk.

Review: breastfeeding duration is a risk factor for cow’s milk allergy.

Don’t bother supplementing breastmilk with formula, or choosing special formulas, to prevent allergy

Cochrane review: no evidence to support using hydrolysed formula instead of exclusive breastfeeding for allergy prevention. Evidence lacks for specific allergy (e.g. food allergy or asthma), but infants at high risk of allergy that aren’t exclusively breastfed might experience less chance of developing allergies in infancy, including cow’s milk allergy, if they are fed prolonged hydrolysed formula compared to cow’s milk formula. Using hydrolysed formula compared to cow’s milk formula for partial or exclusive feeding is also associated with reduced infant allergy and cow’s milk allergy. Evidence is poor in this area, however.

Review: low quality evidence. No consistent evidence that partially or extensively hydrolysed formula reduces risk of allergic (e.g. cow’s milk allergy) or autoimmune disease (e.g. eczema) in high risk infants. So, findings in contrast to Cochrane review and current US Food and Drug Administration guidelines.

Keep the stress levels low

Review: exposure to prenatal maternal psychological stress is associated with increased risk of eczema, allergic rhinitis, wheeze and asthma in offspring. Exposure to anxiety and depression had greatest association. The risk is higher in third trimester, possibly due to cumulative stress over the pregnancy.

Review: Association between pre-natal maternal distress and offspring wheeze/asthma and atopic dermatitis. Bereavement over loss of a child significantly associated with later allergenic disease. Risk of allergenic disease increases as stress accumulates over pregnancy. Most research is in asthma/wheeze so more needed in other allergenic diseases like allergic rhinitis and food allergy.

Review: pre-natal maternal stress (e.g. negative life evets, anxiety/depression, bereavement, distress and job strain) is associated with atopic disorders in offspring (e.g. asthma, wheeze, atopic dermatitis, allergic rhinitis and IgE). Higher quality evidence needed.

Miscellaneous stuff

Review: formula feeding in hospital and caesarean delivery are risk factors for cow’s milk allergy. Prematurity was protective.

Large cohort study: food allergy is positively associated with caesarean delivery, large for gestational age and low 5-min Apgar score. Food allergy negatively associated with preterm birth <32 weeks.

Reviews: development of allergy might not just be to do with the types of food consumed or not consumed by mum and/or bub, factors such as exposure to traffic-related air pollution and second-hand smoke. More research is needed in the area of environmental susceptibility factors though.

Review: no evidence on methods to prevent tree nut allergy.

Review: early life food sensitisation (first 2 years) associated with increased risk of infantile eczema, childhood wheeze/asthma, eczema and allergic rhinitis and young adult asthma. Food sensitization in the first 2 years of life can identify children at high risk of subsequent allergic disease who may benefit from early life preventive strategies.

Children with atopy (a tendency or disposition to develop an allergy) have 30-50% greater chance of developing ADHD later in life

Asthma, eczema and rhinitis are associated with ADHD in childhood

Can have some comfort in that some allergies might not last forever. Cow’s milk allergy (>50% of children are no longer allergic by age 5-10 years), egg (50% by age 2-9 years), wheat (50% by age 7 years) and soy (45% by age 6) with continued resolution into adolescence. But others tend to persist into adulthood or have low rates of childhood resolution: peanut allergy (20% by4 years), tree nut allergy (10%) and allergy to seeds, fish and shellfish are considered persistent.

Review: Allergy immunotherapy (‘cure’ for allergy) doesn’t reduce risk of developing allergenic disease.

Review: Vit E supplementation during pregnancy can prevent asthma.