Breastfeeding Changes How Baby Genes Work, Study Finds

A new global study found scientists can actually tell which kids were exclusively breastfed because of changes to their genetic markers. The implications of the study are still being analyzed by scientists but it comes amid growing conversation about the impact of vaccines and food on babies and kids.

An estimated 130 million babies are born each year and one of the first decision parents make is to breastfeed their child, give them formula or do a combination of both. Over 80 percent of mothers breastfeed their child at some point, according to data from the Centers for Disease Control and Prevention (CDC), but less than 30 percent exclusively breastfeed their child through age 6 months. Advice to mothers has shifted over the years, going from “breast is best,” to “fed is best,” to promote a less stigmatized approach to mothers who feed their babies formula.

Proponents of breastfeeding argue that it’s better because it provides immunity support to babies early in life and a recent study found that it may have lasting biological marks on how a baby’s genes function.

A large international study published in Clinical Epigenetics found that babies who were exclusively breastfed for at least three months showed detectable changes in gene activity years later. Epigenetics are chemical changes that influence how genes are turned on or off.

What the Breastfeeding Study Found

The study analyzed blood samples from more than 3,400 children across 11 countries, comparing those who were exclusively breastfed for at least three months with those who were not. Researchers identified differences in DNA methylation, a key epigenetic mechanism that helps regulate gene activity without altering genetic code.

DNA methylation acts like a dimmer switch for genes, turning their activity up or down. In this case, the changes were found on genes involved in immune system function and development. Researchers took cord blood at birth for the participants of the study and these epigenetic markers were not present at birth, indicating they emerged after breastfeeding began rather than being inherited.

"Our findings show that babies who are exclusively breastfed carry epigenetic changes associated with that experience," Dr. Doretta Caramaschi of the University of Exeter, a co‑lead author of the study, said in a statement. However, she emphasized that the research does not show whether these changes directly improve immunity or development.

To fully understand the biological impact of breastfeeding, Dr. Mariona Bustamante, of ISGlobal, said in a statement that researchers need to study “more diverse groups.”

“Our results are new and interesting, but we do need to interpret them with some caution,” Bustamante said.

The study analyzed whether babies were breastfed and for how long. Scientists then measured DNA methylation marks when the kids were 5 to 12 years old and compared the samples to the blood taken from the umbilical cord at birth.

Benefits of Breastfeeding

While the gene‑focused findings are new, breastfeeding's health benefits are well established. According to the CDC, breastfed infants have lower risks of asthma, obesity, Type 1 diabetes, severe respiratory infections, ear infections and sudden infant death syndrome (SIDS).

The CDC reports that women who breastfeed have reduced risks of breast and ovarian cancer, Type 2 diabetes and high blood pressure. The agency notes that the longer breastfeeding continues, the greater the protective effects for both mother and child.

Researchers involved in the gene study stressed that their findings provide biological context rather than proof of new health outcomes. Previous research has already linked breastfeeding to short‑ and long‑term health advantages, but the epigenetic changes help explain how early feeding might influence the body at a molecular level.

The debate over breastfeeding or formula is one that any mom who’s online has experienced or seen on social media and many people have passionate opinions on the topic. Health and Human Services Director Robert F. Kennedy Jr. has advocated for women to breastfeed and criticized baby formula for being inferior to breast milk.

"We at HHS are encouraging mothers to breastfeed as long as possible because there is no better food for your brain, for your gut microbiome, for your physical growth, for your emotional growth, than what's in God-given breast milk,” Kennedy said in December while urging airports to expand facilities for nursing mothers.

How Long Should You Breastfeed?

While there are benefits to breastfeeding, including immunity passing from mother to baby, pediatricians note that it’s a personal decision that includes many factors. Some women can’t breastfeed, others choose not to for a variety of reasons, including that they just don’t want to, and many pediatricians support however a mother chooses to feed their child.

For women who choose to breastfeed, the CDC advises exclusively breastfeeding for about the first six months and continued breastfeeding until age 1 or longer. At 6 months old, breastfeeding (or formula) will be supplemented by the introduction of solid foods.

The Cleveland Clinic similarly notes that many medical organizations, including the American Academy of Pediatrics and the World Health Organization, support breastfeeding for up to age 2 or beyond when possible, emphasizing that benefits accumulate over time rather than stopping at a fixed endpoint.

How to Stop Breastfeeding

Stopping breastfeeding-often called weaning-is a personal decision influenced by work, health, family needs and choice. The CDC advises that weaning is often easiest when done gradually, allowing both milk supply and the baby's feeding patterns to adjust. The CDC advises dropping one breastfeeding-or pumping-session at a time to help prevent mastitis and adjusting to individual needs.

While the study indicated that decisions made in the earliest times of a person’s life can have lasting impacts, the study’s authors have noted that there needs to be more research into identifying what the findings really mean for health outcomes. The study also notes that feeding is just one aspect of what influences early development: Environment, lifestyle and even social factors can play a role.

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This story was originally published April 20, 2026 at 4:32 PM.