Review shows low odds of infants having allergic reactions to food proteins in breastmilk

Levels of food proteins in breastmilk appeared much lower than the dose required to elicit an IgE-mediated allergic reaction among infants, according to a systematic review in The Journal of Allergy and Clinical Immunology: In Practice.

Although such reactions are possible, the researchers estimated that the probability of food-allergic infant reacting to breastmilk from a woman consuming the relevant allergen would be less than 1:1,000. Still, researchers warned that evidence is sparse and no definitive conclusions can be drawn.

Aysylu Gamirova, BSc, a fifth-year student in the department of pediatrics and pediatric infectious diseases at the Sechenov First Moscow State Medical University Institute of Child’s Health, and colleagues conducted a systematic review of 32 observational and interventional studies of food proteins in human breastmilk.

Fourteen of these studies examined beta-lactoglobulin (BLG) and casein cow’s milk proteins, nine examined ovalbumin (OVA) and ovomucoid (OM) egg proteins, four examined Ara h 2 and Ara h 6 peanut proteins, two examined gliadin wheat protein, and three examined both BLG and OVA proteins.

Observational studies of cow’s milk proteins found BLG in 41.5% of their breastmilk samples, with an overall probability of 1:5,712 for eliciting an allergic reaction in infants allergic to BLG. Interventional studies found BLG in 52% of their samples, with an overall probability of 1:2,893. The one study involving casein showed that levels were too low to elicit a reaction in most children.

The egg protein studies found detectable levels of OVA ranging from 0.1 ng/mL to 29.82 ng/mL in 25.3% of samples. OM concentrations ranged from 0.1 ng/mL to 2.88 ng/mL in the interventional studies and from 0.3 ng/mL to 37 ng/mL in the observational studies.

The levels in the interventional studies were not high enough to enable an estimation of the probability of an allergic reaction, the researchers wrote, but the single observational study yielded a probability of 1:3,846 for an allergic reaction in response to OVA in breastmilk among infants with an OVA allergy.

The peanut protein studies, which all were interventional, reported Ara h 2 in 12.5% of samples and Ara h 6 in 28.3% of samples. Ara h 2 levels ranged from 0.1 ng/mL to 2,602 ng/mL, and Ara h 6 concentrations ranged from 0.1 ng/mL to 79 ng/mL. The researchers, then, concluded a 1:1,000 probability for an IgE-mediated allergic reaction among infants with a peanut allergy.

One of the two studies of gliadin did not find levels above an eliciting dose of 1% of allergic individuals (ED01). The other study found gliadin levels above ED01 in 6.1% of breastmilk samples. The probability of an allergic reaction due to this protein would therefore be 1:1,720 among infants with a gliadin allergy, according to the researchers.

The overall levels of food proteins in breastmilk were much lower than the doses required for eliciting IgE-mediated allergic reactions in most of the breastmilk samples, the researchers said. However, the high heterogeneity between the studies meant that the evidence was limited.

Also, the researchers noted that their findings only related to single-dose exposures and do not account for repeated low-dose ingestion after infants breastfeed multiple times each day. This review, the researchers cautioned, should not be seen as a recommendation for clinical practice but as an exercise in revealing “gray areas” and unmet evidence in the field.

Due to this sparse and inconclusive evidence, the researchers wrote, well-controlled trials are needed to investigate the effects of food proteins in breastmilk on allergic reactions in children. Otherwise, evidence-based clinical guidelines for treating breastfeeding children with food allergy will not be possible, leading to inappropriately restricted maternal diets or breastfeeding cessation in routine clinical practice.