Seal milk more refined than breast milk

Researchers at the University of Gothenburg have discovered that milk from grey seals in the Atlantic Ocean may be more potent than breast milk. An analysis of seal milk found approximately 33 per cent more sugar molecules than in breast milk. Many of these sugars are unique and may pave the way for even better infant formula for babies.   

During the 17 days that grey seal pups suckle, they need to get their digestive systems up and running and build up an immune system to protect them against diseases and other dangers they may encounter in the North Atlantic. It is reasonable to suspect that their mother's milk is extremely refined to accomplish this task. A new study in Nature Communications shows that this is indeed the case.

“Our analysis shows that grey seal milk is extraordinary. We identified 332 different sugar molecules, or sugars, compared to about 250 in breast milk. Two-thirds were completely unknown previously. Some of these molecules had a previously unseen size of 28 sugar units, which exceeds the largest known sugar units in breast milk, which are 18 units in size,” says Daniel Bojar, senior lecturer in bioinformatics.

Protects against bacteria

Oligosaccharides are a type of sugars found in the milk of all mammals that contributes to the development and health of offspring. These sugars have important functions, including protecting against viruses and bacteria, cultivating the initial flora of the body's microorganisms and promoting the development of the stomach and intestinal tract. Despite their importance, there are gaps in our knowledge of the diversity of milk sugar in animals, mainly because a limited number of studies have been conducted on non-human mammals.

“For the first time, we have been able to analyse the milk sugars in the milk of a wild mammal throughout the entire lactation period. This is important because the composition of the milk changes as the calf gets older,” says Daniel Bojar.

The milk changes

Milk was collected on several occasions from five wild grey seals off the coast of Scotland throughout their lactation period. Using mass spectrometry, the researchers were able to characterise 240 of the sugars found structurally. Using a combination of analyses and AI models, the study also reveals that the composition of seal milk undergoes coordinated changes throughout the lactation period, similar to that of breast milk.

“The sugars bind to various proteins found in, for example, the immune system. We have tested the newly discovered sugar molecules on human immune cells and found that they can regulate the cells' response to various threats. The findings suggest that wild marine mammals, which are exposed to extreme environmental stresses and high exposure to external dangers, have developed a complex milk to protect their rapidly growing young,” says Daniel Bojar.

Support for the immune system

This analysis also showed that several of the sugar molecules have powerful properties against disease-causing bacteria.

The research paves the way for the discovery of new bioactive compounds with potential applications in infant nutrition, infection control and immune system support. In the future, these newly discovered sugar molecules could be added to breast milk substitutes to strengthen the immune system in infants. The milk sugars could also be given to adults to keep the gastrointestinal system healthy.

“The study highlights the untapped biomedical potential hidden in understudied wild species. Our research group is the only one in the world to analyse milk sugars from these uncharacterized mammals using mass spectrometry in that depth. We have done this for ten different mammals, and we find unique sugar molecules every time. We will continue. We have milk from another 20 mammals in the freezer,” says Daniel Bojar.