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Current government advice is to exclusively breastfeed infants for the first 6 months of life if possible1 and that there is no reason for women who are breastfeeding their babies to avoid eggs or other allergenic foods unless they themselves are allergic to them2.
It is known that maternal antigens to potential food allergens, such as eggs, can pass into breast milk and it has been suggested that infants might be sensitised to foods by exposure to these antigens in their mother’s milk. Until recently, there has only been limited evidence to support this suggestion and the authors of a Cochrane review on the subject in 2012 concluded that there is currently insufficient evidence to recommend antigen avoidance diets during breastfeeding to reduce the risk of subsequent infant allergies3. They observed that further research in this area is required and two studies in 2017 supported the hypothesis that mothers who eat eggs when breastfeeding may help protect their babies against future egg allergy.
The first study4, a randomised controlled trial (RCT) undertaken at the University of Western Australia, investigated how maternal dietary egg ingestion during early breastfeeding influences egg protein (ovalbumin) levels detected in human breastmilk and whether this influences sensitivity or tolerance to egg protein in the infant.
Women were allocated to a dietary group for the first six weeks of lactation: high-egg diet (> 4 eggs per week), low-egg diet (one-three eggs per week) or an egg-free diet. Breastmilk samples were collected at 2, 4 and 6 weeks of lactation for the measurement of ovalbumin. Blood levels of egg-specific immunoglobulin E (a measure of sensitisation to egg) and immunoglobulin G4 (IgG4) (an indication of protection against allergy and tolerance to egg) were measured in the infants at 6 weeks as well as before introducing egg in solids at 16 weeks.
Average maternal egg consumption correlated with breastmilk ovalbumin concentration; for each additional egg ingested each week, there was an average 25% increase in ovalbumin concentration. Ovalbumin concentrations were significantly higher in the breastmilk of the 'high-egg' group compared with the 'egg-free' group. Blood levels of egg-specific IgG4 in the infants were positively related to maternal egg consumption, with an average 22% increase in infant egg-specific IgG4 per additional egg consumed each week.
The researchers concluded that increased maternal egg consumption is associated with increased breastmilk ovalbumin, and with markers of immune tolerance in infants. These results highlight the potential for maternal diet to benefit the development of oral tolerance in the infant during lactation.
The second study5, carried out in mice at Boston Children’s Hospital, found that lactating mothers sensitised to egg protein (ovalbumin) passed IgG4 antibodies on to their offspring, allowing them to tolerate the food.
Through a series of experiments in a mouse model, which had similar features to human food allergy, the research team showed that pregnant and breastfeeding mice exposed through the skin barrier to ovalbumin transferred protective IgG4 antibodies to their babies through their breastmilk. The antibodies caused the babies to produce allergen-specific regulatory T immune cells, also known as Treg cells, which appears to have enabled them to tolerate the allergenic food. The babies from sensitised mothers who were then subjected to skin sensitisation and oral challenge to ovalbumin showed a much smaller allergic response to the allergen.
Breastmilk appeared to protect against food allergy even when it was fed to unrelated offspring whom had not experienced in utero exposure to maternal IgG4 antibodies. Furthermore, when mothers had not been sensitised, but were supplemented with ovalbumin-specific IgG4 antibodies whilst breastfeeding, the babies were also protected.
Even after the mother’s antibody disappeared from the babies’ circulation, the babies showed no allergic response to skin or oral challenges with ovalbumin, suggesting a long-lasting effect.
The researchers also examined mice born to allergen-exposed mothers nursed from mothers that had never consumed allergenic foods. They still saw protection from the in utero exposure, but the protection was better when the mice were also exposed through breastfeeding. The researchers commented that combining both in utero and breastfeeding exposure gave optimal induction of food tolerance.
Human breast milk was also protective in mice whose immune systems were tailored to respond to human antibodies, suggesting that the mouse findings may translate to human infants.
3. Kramer and Kakuma (2012) Maternal dietary antigen avoidance during pregnancy or lactation, or both, for preventing or treating atopic disease in the child. Cochrane Database Syst Rev. 2012 Sep 12;9:CD000133. doi: 10.1002/14651858.CD000133.pub3.
4. Metcalfe JR et al. (2016) Clin Exp Allergy. 2016 Dec;46(12):1605-1613. doi: 10.1111/cea.12806. Epub 2016 Oct 7.
5. Ohsaki A et al. (2017) Maternal IgG immune complexes induce food allergen–specific tolerance in offspring doi: 10.1084/jem.20171163 http://jem.rupress.org/content/early/2017/11/17/jem.20171163