Breast Milk Fat Linked to Long-Term Immune Benefits in Early Life: Study

Breast milk is widely recognized as the best source of nutrition for newborns, but scientists have now identified a naturally occurring fatty acid that may also play a key role in shaping the developing immune system.

A new study published in Science suggests that trans-vaccenic acid (TVA), a fat commonly found in breast milk, helps train immune cells during early life and provides long-lasting protection against infections in mice.

Researchers from the University of Chicago investigated the effects of TVA, a naturally occurring trans fatty acid found in meat and dairy products from grazing animals and abundant in human breast milk. Nursing mother mice were fed a TVA-enriched diet, allowing the fatty acid to pass to their pups through breast milk. The team found that this exposure promoted the development of a broader population of immune cells, particularly CD4+ T cells, which play a central role in adaptive immunity.

Further genetic analyses showed that TVA reprogrammed these immune cells during a critical developmental window, shifting them toward stronger responses against bacteria and viruses.

Notably, the benefits were only seen when TVA was delivered through breast milk after birth. Mice exposed to TVA during pregnancy but nursed by mothers without TVA-enriched milk did not show the same immune advantages, suggesting that postnatal exposure during breastfeeding is essential for this long-term immune "imprinting."

The researchers also analyzed breast milk and blood samples from human mothers and infants. Higher levels of TVA in breast milk were associated with increased TVA levels in infants' blood. Among preterm infants, higher circulating TVA levels were linked to immune changes similar to those observed in mice and were associated with a lower risk of bronchopulmonary dysplasia, a chronic inflammatory lung disease common in premature babies.

While the findings are based primarily on animal studies, the researchers say they open the door to exploring whether TVA supplementation during breastfeeding or inclusion in infant formula could one day help support early immune development in humans.

REFERENCE: Fan, H., et al. (2026). Maternal trans-vaccenic acid shapes neonatal T cell development and early-life immune imprinting. Science. DOI: 10.1126/science.aea4041. https://www.science.org/doi/10.1126/science.aea4041