It is an established medical fact that breastfeeding offers long-term positive medical benefits to babies, which can extend well into adulthood. For instance, breastfed babies are less likely to develop asthma, obesity, and autoimmune disease later in life compared to babies who are exclusively fed formula. Now, a new study reveals new insights into the biological mechanisms that may explain these immunological benefits.

More abundant immune cells

Breast milk contains over 200 different ingredients, including protein, fat, carbs, vitamins, minerals, enzymes, and hormones, although the exact composition will vary from mother to mother and even from one feeding session to another throughout the day.

According to the WHO, breast milk is the natural first food for babies, providing all the energy and nutrients that an infant requires for the first half-year of life. Breast milk continues to be an important part of an infant’s diet, providing half of their nutritional needs during the second half of the year, and one-third during the second year of life.

Breastfeeding transmits elements of the mother’s own microbiome and immune system, providing probiotics to support the growth of beneficial bacteria and kickstarting a baby’s microbiota. The mother transfers her antibodies to her baby through breast milk, and this is particularly true of colostrum, the first milk. For instance, breast milk is high in immunoglobulin A (IgA), which protects the baby from getting sick by forming a protective layer around the nose, throat, and digestive system.

In a new study published this week in the journal Allergy, researchers at the University of Birmingham have discovered that regulatory T cells — a specific type of immune cell which plays a role in regulating or suppressing other cells in the immune system — expand in the first three weeks of life in breastfed babies and are twice as abundant as in formula-fed babies.

According to the authors, these cells control the baby’s immune response so it doesn’t go overboard when it comes into contact with maternal cells transferred through breastmilk, thereby reducing inflammation.

What’s more, the researchers also noticed that bacteria called Veillonella and Gemella, known to support the function of regulatory T cells, are more abundant in the gut of breastfed babies.

“The influence of the type of milk received on the development of the immune response has not previously been studied in the first few weeks of life,” said senior author Gergely Toldi, a researcher at the University of Birmingham and consultant neonatologist at Birmingham Women’s and Children’s NHS Foundation Trust.

“Prior to our research the outstanding importance and the early involvement of this specific cell type in breastfed babies was unknown. We hope this invaluable new insight will lead to an increase in rates of breastfeeding and will see more babies benefit from the advantages of receiving breastmilk.”

“Furthermore, we hope for those babies who are formula-fed, these results will contribute to optimizing the composition of formula milk in order to exploit these immunological mechanisms. We are very grateful for the mums and babies who contributed to this special project.”