“Cow’s milk allergy is among the most common food allergies in young children, and cow’s milk protein is often introduced before any other allergens or foods, in the form of cow’s milk-based infant formulas,” explains Karen M. Switkowski, PhD, MPH. “In fact, many infants are exposed to formula within hours or days after birth. Our team was interested in studying how the timing of first milk exposure was related to later milk allergy symptoms, especially given all the recent research on peanut allergy that has led to new allergy prevention paradigms supporting the early introduction of peanuts at 4-6 months of age. We wanted to know whether the idea of ‘earlier is better’ also applied to cow’s milk.”

For a study published in The Journal of Allergy and Clinical Immunology: In Practice, Dr. Switkowski and colleagues examined the outcome of parent-reported adverse reactions to cow’s milk. “These parent observations likely captured immunoglobulin E (IgE)-mediated reactions, as well as other ‘non-IgE’ allergic reactions that can be harder to recognize,” Dr. Switkowski says. “While both types of allergies to cow’s milk will almost always resolve with time, they can be associated with dermatologic, gastrointestinal, and respiratory symptoms, as well as potentially life threatening anaphylaxis. Kids with food allergies may also experience nutrient deficiencies or have their growth impacted. Therefore, we felt it was important to study cow’s milk allergy, even though it, fortunately, generally resolves by mid-childhood.”

Assessing the Timing of Cow’s Milk Protein Introduction

The study team used data from approximately 1,300 children participating in the Boston-area Project Viva cohort, which follows a group of mothers and their children born in 1999-2002. Relying on questionnaires that had been administered to mothers when their children were infants, they were able to assess timing of cow’s milk protein introduction, either from milk-based formula or other cow’s milk products, and to categorize the first exposure as occurring within 2 weeks of birth, between 2 weeks and 6 months of age, or after 6 months. “Additionally, we were able to use data from a research visit that had been performed in the hospital shortly after delivery, indicating whether the infant had received any formula during that time.”

Notably, babies who were given formula in the hospital in the days after birth versus those who were not had different rates of later reactions to cow’s milk when the timing of cow’s milk introduction was considered “Babies who did get formula in the hospital just after birth had the lowest risk for developing adverse reactions to it, but only if they continued to receive a cow’s milkbased formula within the 2 weeks after birth,” notes Dr. Switkowski.

Infants 6 Months and Older Had Highest Risk for Adverse Reaction

“Among babies who did not get any formula just after birth, the best time to introduce cow’s milk protein seemed to be later, sometime between 2 weeks and 6 months. However, infants who were introduced to cow’s milk at or after 6 months of age had the highest risk for later adverse reactions to cow’s milk (Figure).”

The study team concludes that “timing is everything” when it comes to introducing cow’s milk to an infant. “Our findings indicate that giving a baby supplemental formula immediately after birth may potentially increase their risk for milk allergy, if the baby goes on to be exclusively breastfed after they leave the hospital,” Dr. Switkowski notes. “On the other hand, babies who continue to get some formula and some breastmilk during the first 2 weeks of life may not be at higher risk for allergy and might even be protected from it.”

Study Supports Current Recommendations for Introducing Cow’s Milk

Dr. Switkowski and colleagues agree that physicians can use their findings to support current recommendations that parents should introduce cow’s milk-based dairy products to their baby, along with other complementary and potentially allergenic foods, between 4 and 6 months of age.

For future research, the study team is particularly interested in exploring the impact of a mother’s diet during and after pregnancy, particularly if a mother is breastfeeding, on babies’ tolerance of cow’s milk and other food allergens. They also plan to examine timing of introduction of other food allergens in relation to later adverse food reactions among babies with different types of feeding.