How Human Breastmilk Can Block Coronavirus’s Replication

A new study further tells us why Covid-19 is not a good enough reason to not breastfeed.

Shin Jie Yong
Nov 27, 2020 · 4 min read
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Photo by NIKOLAY OSMACHKO from Pexels

Breastfeeding does many wonders for the baby and mother, ranging from emotional, immunological, and general health support.

For the newborn, it encourages the development of the immune system and gut microbiome. It lowers the risk of diabetes (type I and II), obesity, leukemia, asthma, atopic dermatitis, improper cognitive development, and ear, respiratory and gastrointestinal infections. For the mother, breastfeeding decreases the risk of breast and ovary cancers, type II diabetes, and postnatal depression. And breastfeeding establishes emotional bonding between the newborn and mother.

Breastmilk is rich in lactoferrin, a protein with diverse biological functions: anti-cancer, neuroprotective, bone support, immunomodulation, antioxidant, and antimicrobial (including bacteria, fungi, parasites, and viruses). So, it’s not a surprise if it fights SARS-CoV-2, which a newly published study has just shown.

What the study did and found

The paper, “The effect of whey protein on viral infection and replication of SARS-CoV-2 and pangolin coronavirus in vitro,” was published a few days ago in Signal Transduction and Targeted Therapy, a highly reputed journal (SARS-CoV-2 is the novel coronavirus that causes Covid-19.)

Herein, researchers from China institutions collected breastmilk samples from eight healthy mothers before the Covid-19 pandemic started. Samples were then skimmed to remove the lipids and retain only the proteins for subsequent experiments.

1. Overall anti-coronavirus effects

In human kidney and lung cells infected with coronaviruses, the study showed that skimmed breastmilk blocked the replication of both SARS-CoV-2 and its relative pangolin coronavirus by 98% compared to the no-treatment group at 0%. As a result, only minimal infectious coronavirus particles were produced.

While such effects are dose-dependent, only small doses of the skimmed breastmilk samples were needed to achieve these maximal effects. Another unanticipated upside is that skimmed breastmilk treatment even helped the infected cells to proliferate healthily.

2. Are the proteins responsible?

After that, the researchers wanted to understand if proteins in the skimmed breastmilk were responsible for the anti-coronavirus effects. They heated the samples at 100°C for 10 minutes to denature the proteins. And these heated samples lost their antiviral effects.

3. Human breastmilk proteins vs. other animals’

Interestingly, commercial goat and cow whey (milk) proteins also blocked the replication of SARS-CoV-2 and pangolin coronavirus, but to a lesser extent than the human skimmed breastmilk. “These results indicated that human whey protein has a high concentration of antiviral factors than those from other species,” the authors stated. Indeed, “human milk is rich in LF [lactoferrin], which is 10–100 fold higher than that in cow and goat milk.”

Breastmilk is rich in lactoferrin, a protein with diverse biological functions: anti-cancer, neuroprotective, bone support, immunomodulation, antioxidant, and antimicrobial.

4. How does human breastmilk stops coronavirus replication?

They did more experiments to decipher the underlying mechanisms of the anti-coronavirus effects. They found that the skimmed human breastmilk could attach to the coronavirus’s spike protein surface to prevent its binding to the ACE2 receptor on the human cell surface. As a result, more than 90% of SARS-CoV-2 and pangolin coronavirus particles failed to bind and infect the human cells.

Even in those remaining 10% coronaviruses that managed to infect the cells, human breastmilk also blocked the virus’s replication inside the cell by arresting its RNA polymerase enzyme. This enzyme is responsible for RNA viruses, which include coronavirus, to replicate themselves. Therefore, the authors wrote, “[human] breastmilk inhibits not only viral entry but also viral replication.”

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A few more considerations

All studies have caveats. In this study, the researchers noted that breastmilk samples were collected from only eight mothers, so the sample size is limited. Besides, as the title stated, this study is an in vitro model. In vitro means outside a living organism, such as in cells cultured in a dish or flask.

Thus, animal models may still be needed to verify the anti-coronavirus effects of human breastmilk. Even if the in vitro results do not fully translate to actual organisms, breastmilk may still thwart coronavirus indirectly via the other biological benefits it provides, as stated in the beginning.

Another point is the skimming process. As lipids in the human breastmilk were removed, it’s unclear if such lipids would influence the proteins' anti-coronavirus properties in human breastmilk. But if anything, the fatty acids in breastmilk — particularly the omega-3s and short-chain fatty acids (SCFAs)— should provide additional benefits to the baby’s immune system.

“These results indicated that human whey protein has a high concentration of antiviral factors than those from other species.”

Can a mother with Covid-19 or SARS-CoV-2 still breastfeed? Yes, thus far, no evidence has found infectious SARS-CoV-2 in breastmilk. While SARS-CoV-2 RNA genetic material can be detected in breastmilk in rare cases, it’s not infectious in cultured cells. For precautions, health authorities have advised mothers with positive or suspected Covid-19 to wear masks and wash hands before breastfeeding. So, unless the mother has certain infections like HIV, cancers, or medication or illegal drug usage, it’s hardly ever a bad move to breastfeed. Covid-19 is not a good enough reason to not breastfeed.

Microbial Instincts

Decoding the microbial angle to health and the microbial world.

Shin Jie Yong

Written by

Freelance medical writer | Published academic author | Neurobiology postgrad in Malaysia | 85+ curated articles on coronavirus | contact: shinjieyong@gmail.com

Microbial Instincts

Decoding the microbial angle to health and the microbial world.

Shin Jie Yong

Written by

Freelance medical writer | Published academic author | Neurobiology postgrad in Malaysia | 85+ curated articles on coronavirus | contact: shinjieyong@gmail.com

Microbial Instincts

Decoding the microbial angle to health and the microbial world.

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