[Research Press Release] Biochemistry: Seal milk rivals human milk in complexity (Nature Communications)

Atlantic grey seal milk rivals human breast milk in sugar complexity, suggests research published in Nature Communications. These findings challenge the previously held assumption that human milk is uniquely complex amongst mammals.

Milk oligosaccharides are a type of sugar that contribute to infant development and health in all mammals. These sugars have critical roles including protection from pathogens, cultivating the initial microbiome, and promoting intestinal tract development. Despite their importance, there are gaps in our knowledge of milk sugar diversity in animals other than humans, mainly because there have been a limited number of studies involving other mammals.

Daniel Bojar and colleagues analyze milk samples from five wild Atlantic grey seals throughout their roughly 17-day nursing period. They discover 332 different sugar molecules and structurally characterise 240. Of these 240, approximately two-thirds (166) had not been previously documented. Some of these molecules reached a size of 28 sugar units, up to 10 units more than the largest known human milk sugars. The authors reveal that the sugar composition of seal milk undergoes coordinated changes throughout the lactation period to fit the changing needs of the infant, similar to the changes seen in human milk. It is also demonstrated that several of these newly discovered sugars possess antimicrobial and immunomodulatory properties, with potential applications in the biomedical sciences.

This study potentially challenges our understanding of mammalian milk evolution, overturning long-held assumptions that human milk is uniquely sophisticated among mammals. The research may also open promising avenues for discovering bioactive compounds with potential applications in infant nutrition, infection control, and immune system support.

• Article
• Open access
• Published: 25 November 2025

Jin, C., Lundstrøm, J., Cori, C.R. et al. Seal milk oligosaccharides rival human milk complexity and exhibit functional dynamics during lactation. Nat Commun 16, 10067 (2025). https://doi.org/10.1038/s41467-025-66075-2

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