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The Science of Breastfeeding

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Globally, an estimated 41% of all babies are breastfed exclusively for six months, and, of this,  ~45% continue to be breastfed until they are two years old.

A growing amount of research continues to demonstrate that breastfeeding can provide numerous health benefits for both mother and baby. These include a secure food resource at the early stages of life, ensuring optimal nutrition for babies, and protection against diseases. Evidence suggests that breastfeeding may also reduce the risk of allergic diseases, obesity, asthma and Type 2 diabetes.

World Breastfeeding Week (WBW) takes place on August 1–7 each year to celebrate the anniversary of the 1990 Innocenti Declaration on the protection, promotion and support of breastfeeding. To mark WBW 2022, Technology Networks interviewed Dr. Alecia-Jane Twigger. Originally from Australia, Dr. Twigger is a postdoctoral researcher in the Khaled group in the Department of Pharmacology, University of Cambridge.

Her research focuses on understanding how factors such as pregnancy and lactation influence mammary gland biology, and breast cancer risk. In this interview, we discuss the science of breastfeeding – how breastmilk is produced, its composition and the links between breastmilk and the immune system.

Molly Campbell (MC): Can you talk about how breastmilk is produced? What triggers this process to occur?

Alecia-Jane Twigger (AT): During pregnancy, physical changes such as the size and structure of the breast occur to ready it for producing milk. On a microscopic level, the epithelial cells of the breast begin to mature and are primed to produce milk in a process called secretory differentiation. After birth of the child and delivery of the placenta, there is a drop in maternal progesterone levels which signals the second process – secretory activation – to enable copious milk production.

Over the course of lactation, the breast is constantly synthesizing milk under the control of the hormone prolactin. When an infant feeds, the sucking stimulation from the infant to the nipple triggers a “let-down”, where the hormone oxytocin signals the breast to eject the milk. There are still many questions remaining as to exactly how each milk component enters the milk, either by being transported from other sources (such as from the mother’s blood) or being actively synthesized by cells in her breast.

MC: Can you discuss what we know, and perhaps don’t know, about the composition of breastmilk?

AJT: We know the broad break down of the components in milk, such as roughly how much fat (3–5%), carbohydrates (6.9–7.2%) proteins (0.8–0.9%) and micronutrients (0.2%) are contained in milk.

As scientific technologies have developed, we are able to better discover and characterize the full variety of these different components. An example of this is that human milk has been recently found to contain not one, but two different secretory cell subtypes.

There is still much work to be done to understand how milk adapts to the needs of the infant and how this may affect long-term growth outcomes. In addition, we still need to better understand how an individual’s milk composition might vary and which factors might affect this, such as ethnicity.

MC: What has science discovered about how the production of breastmilk alters the cells of the mammary glands?

AJT: It is difficult to get material to study this in humans, therefore it is quite hard to answer this question. Having said this, evidence from mouse studies suggest that lactation has a long-term effect on the mammary cells, from the proteins they produce through to their DNA. These changes might facilitate a more rapid mature milk production for future children.

MC: What do we know about why some women are unable to produce breastmilk? How might this research help support these women?

AJT: Some women may have difficulties to breastfeed, which may arise due to incorrect attachment of the child to the breast either due to positioning or anatomical difficulties, such as if the infant has tongue tie. In five percent of the cases, the breast may have tissue damage or a lack of tissue development, classified as primary lactation insufficiency.

If none of these apply and the individual is still unable to lactate, they may have secondary lactation insufficiency where the breast may not produce enough milk. The cause behind this is still unknown and further research into how the breast changes prior to and during lactation could help us develop tools to assist these women who are unable to breastfeed.

MC: Can you talk about the immune system and how this is related to breastmilk production and breastfeeding?

AJT: Human breastmilk contains a number of immunological components, including a full complement of immune cells, cytokines, antibodies and proteins such as Lactoferrin and sIgA. These components are thought to help compensate for developmental delays and protect the infant in the early stages of life. How the immune system impacts the overall health of the breast and contributes to milk production is still unknown.

MC: What are the current challenges that researchers face when studying breastmilk? How do you hope we will overcome these challenges?

AJT: One of the main challenges in breastmilk research is not having an ideal model system to study milk production. Some experiments that will help progress the field cannot be done by studying humans alone, and therefore we can understand more about breast function and milk production by studying animals. However, there are many species differences in the composition of milk that must be considered. A greater investment into developing models of human milk production in the lab will be key to progressing the field.

MC: Where can we learn more about breastmilk research?

AJT: There are many rich resources available to help you learn more about breastmilk research, such as:

Dr. Alecia-Jane Twigger was speaking to Molly Campbell, Senior Science Writer for Technology Networks.