Boston, MA: New research in The Journal of Allergy and Clinical Immunology has shown that early and consistent exposure to cow's milk in children appears protective against adverse reactions to cow milk.
This prompted researchers to suggest that mothers intending to exclusively breastfeed might avoid cow's milk-based formula supplements post-birth. "When deciding the timing of cow's milk introduction to the diet, parents might consider whether an infant was given supplemental formula after birth." the researchers wrote.

Current guidelines have suggested early introduction to potentially allergenic foods, but there is no clear establishment of the optimal timing, amount, and exposure routes for foods other than peanuts. Often, cow's milk is the first allergic food introduced through infant formulas.
Considering the above, Karen M. Switkowski, Harvard Medical School and Harvard Pilgrim Health Care Institute, Boston, MA, and colleagues aimed to examine the timing of cow's milk protein introduction (CMPI), including interaction with formula supplementation after delivery, in relation to reported cow's milk adverse reactions (CMARs), throughout childhood.
For this purpose, the researchers assessed the timing of CMPI (<2wks, 2wks-<6mos, ≥6mos) among children in the Boston, MA-area Project Viva cohort with questionnaires administered in infancy. Outcomes included 1) parent-reported CMAR via annual questionnaires from 2-13yrs (n=1298); and 2) milk sensitization (n=505) and IgE-mediated milk allergy (n=491) at ∼8yrs.
Multivariable logistic regression models were used after adjusting for parental atopy history, delivery mode, gestational age at delivery, child race, and census tract median household income. Effect modification was investigated by ever/never breastfed status and formula supplementation in the delivery hospital.
Key findings of the study include:
· 32% were introduced to cow's milk protein at <2wks, 38% at 2wks-<6mos, and 30% at ≥6mos.
· Compared to children with CMPI <2wks, children with CMPI ≥6mos had a higher risk of CMAR at 2-5yrs (OR: 2.4).
· Children who were given formula after delivery + CMPI <2wks had the lowest risk overall.
· Among children not given formula after delivery, CMPI 2wks-6mos appeared most protective. Results were similar among ever-breastfed children.
· Timing of CMPI was not associated with milk sensitization or IgE-mediated milk allergy in mid-childhood.
The researchers conclude, "early, consistent cow's milk exposure appears protective against adverse reactions to cow's milk."
Reference:
Switkowski KM, Oken E, Rifas-Shiman SL, Camargo CA Jr, Gold DR, Sordillo JE, Lightdale JR. Timing of Cow's Milk Protein Introduction and Childhood Adverse Reactions to Cow's Milk. J Allergy Clin Immunol Pract. 2022 Jun 29:S2213-2198(22)00644-4. doi: 10.1016/j.jaip.2022.06.022. Epub ahead of print. PMID: 35779778.