Breastfeeding and risk of Food Allergy
A retrospective cohort study (46,616 children) in Japan in September 2019 found that breastfeeding, especially colostrum, had prophylactic effects (preventive) on food allergy only among high-risk children with infantile eczema whereas prolonged breastfeeding increased the risk of food allergy.
From what I can understand from the full text of the Japan study, the researchers are trying to determine the impact of breastfeeding on food allergy, taking into account whether the child has infantile eczema. We know that breast milk contains many active immune factors such as cytokines, inflammatory mediators, signaling molecules, and soluble receptors which may reduce the risk of allergic diseases (but results are conflicting and difficult to control variables in a study involving babies and breastfeeding since baby's health, mom's health and breast milk quality cannot be controlled). One of the difficulties of studying breastfeeding and food allergy is figuring out where eczema comes in (because babies who have eczema may have higher risk of food allergy due to increased sensitization).
So, the researchers analysed the data through questionnaires and came to the conclusion that breastfeeding has protective effect for high-risk children but prolonged breastfeeding increased the risk of food allergy. As to why, could be many factors (including unknown ones!) such as exclusive breastfeeding meant later introduction of cow's milk, which may increased the allergy risk.
The frustrating thing is that studies involving infants are usually by associations and difficult to control. The takeaway for me is that there is no need to feel guilty if you do not persist in breastfeeding, because even just the colostrum have protective effect for your eczema baby.
Here are some milk-free recipes books: