Breastfeeding is often linked with better health for both mothers and babies, but it does not protect all women against breast cancer. The reason remains unknown. Since breast cancer in young women is on the rise, understanding why breastfeeding is protective in some women but not others is critical.

A new study, led by a team of researchers from The Tisch Cancer Institute at the Icahn School of Medicine at Mount Sinai and published in the journal Nature Communications, addressed this question.

The study was performed in mice, which exhibit a similar phenomenon: lactation strongly protects some mice against breast cancer, but others are more susceptible. The researchers studied female mice that had the same basic DNA but different types of mitochondria—small parts of cells that help make energy and play a role in how cells work. The team found that the way the body responds to breastfeeding could change depending on the mother’s mitochondria.

In mice with specific types of mitochondria, the researchers found, lactation allowed a certain group of cells similar to those found in postpartum breast cancer in humans to expand and grow, explains Edmund Jenkins, PhD, Assistant Professor of Medicine (Hematology and Medical Oncology) at the Icahn School of Medicine at Mount Sinai. Dr. Jenkins served as the bioinformatics expert on the study.

“We’ve always thought that breastfeeding is good for all women when it comes to lowering breast cancer risk,” said senior author Doris Germain, PhD, Professor of Medicine (Hematology and Medical Oncology) at the Icahn School of Medicine at Mount Sinai. “But our study shows that it really depends on a woman’s metabolism and how her body responds to lactation at the cellular level.”

The researchers also discovered that they could change the way the body reacts during breastfeeding by using a natural dietary supplement. In the mice that were at higher risk of developing postpartum breast cancer, this treatment switched their response from harmful to protective. This finding opens the door to a possible way to help more women benefit from breastfeeding by supporting their bodies in the right way.

“Our research raises the possibility that one day, doctors might be able to identify women whose breastfeeding response puts them at risk and then offer them a simple, natural dietary intervention to change that,” said first author Mrittika Chattopadhyay, PhD, Assistant Professor of Medicine (Hematology and Medical Oncology) at the Icahn School of Medicine at Mount Sinai.

The team is now studying human breast milk with the goal of identifying milk metabolites that can show whether a woman’s body is reacting to breastfeeding in a way that is helpful or harmful. They also plan to develop a study in humans. One question then will be whether, because this dietary supplement may impact the development of the child, it should be tested only in mothers after they have stopped giving milk to their newborns.

The National Institutes of Health (NIH) funded the research.

Source: Mount Sinai