Gut Bacteria Gas Linked to Pregnancy Hormone, Mood Regulation & PPD

by Ella

Summary: Researchers have discovered that gut bacteria produce a hormone involved in pregnancy and the treatment of postpartum depression by modifying steroids in bile. This research highlights the microbiome’s role as an endocrine organ influencing human health, suggesting that targeting gut bacteria could help treat mental health conditions. The study opens new avenues for understanding gut-brain interactions.


Key Facts:

Hormone Production: Gut bacteria produce allopregnanolone, a hormone linked to pregnancy and mood regulation.
Microbiome’s Role: The microbiome acts as an endocrine organ, influencing human health and behavior.
Potential Therapies: Research suggests targeting gut bacteria could help treat mental health conditions like postpartum depression.


New research led by scientists at Harvard Medical School has revealed that gas released by some gut bacteria can stimulate other bacteria to produce a hormone involved in pregnancy and the FDA-approved treatment for postpartum depression. This discovery underscores the gut microbiome’s potential as an endocrine organ capable of influencing human health in significant ways.


Gut Bacteria and Hormone Production

The research shows how gut bacteria can transform steroids in bile into new hormones, thereby functioning similarly to an endocrine organ. This adds to the growing body of evidence that gut microbiota significantly impact human biology and health. Specifically, this study identified that gut bacteria produce allopregnanolone, a hormone crucial for pregnancy and mood regulation.


Microbiome’s Endocrine Function

“Our cells make steroids only in the oxidative direction, that is, losing electrons, whereas we’ve shown that gut bacteria can go in the reverse direction, known as reduction, or gaining electrons — making the bacterial transformation unique,” explained Sloan Devlin, HMS associate professor of biological chemistry and molecular pharmacology and senior author of the study.

The team found that bacteria can alter corticoids in bile—steroids involved in immune function and metabolism—into progesterone derivatives, which are sex hormones and neurosteroids affecting the brain and nervous system.

Link to Pregnancy and Mental Health

In collaboration with Andrea Edlow, HMS associate professor of obstetrics, gynecology, and reproductive biology at Massachusetts General Hospital, the team explored allopregnanolone production during pregnancy. They analyzed fecal samples from pregnant women and found significantly higher levels of allopregnanolone in women during their third trimester. The study suggests that gut bacteria contribute to the production of this hormone during pregnancy.

Low levels of allopregnanolone have been linked to postpartum depression and other mood disorders. Notably, allopregnanolone is used as an FDA-approved drug, brexanolone, to treat postpartum depression. This finding implies that manipulating the gut microbiome could potentially prevent or treat such mental health conditions.

Research Implications and Future Directions

The study opens up new possibilities for microbiome-targeted therapies for neurological conditions like depression. Devlin and his team plan to expand their research by tracking participants throughout their pregnancy and postpartum period to better understand the role of gut bacteria in allopregnanolone production and postpartum depression risk.

“Our work suggests that the microbiome acts as an additional endocrine organ,” said Devlin. “We hope this work convinces people that gut bacteria modify steroids to produce molecules that can affect host functions, including mood and behavior.”

Behind the Chemistry

The researchers identified the genes responsible for these chemical transformations and found that G. pamelaeae and E. lenta bacteria require hydrogen, a gas produced by other bacteria during food digestion. This indicates that the interaction between different bacterial species and the gases they produce can significantly impact human health.

Support and Funding

The study, published on May 24 in Cell, received funding from the National Institutes of Health, the Alfred P. Sloan Foundation, the Simons Foundation, the National Science Foundation, and the Resnek Family Center for Primary Sclerosing Cholangitis Research. Additional authors included experts from various institutions, highlighting the collaborative effort behind this groundbreaking research.


This study highlights the complex and critical role of the gut microbiome in human health, particularly in pregnancy and mental health. By understanding the mechanisms through which gut bacteria influence hormone production, researchers can develop new strategies to improve maternal and mental health outcomes. This research underscores the potential of the microbiome as a target for innovative treatments for conditions like postpartum depression, paving the way for future advancements in microbiome science and its application in healthcare.


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