Recent studies reveal that gut bacteria play a crucial role in recycling discarded sex hormones back into the bloodstream. Researchers have discovered an alarming increase in these hormone-recycling bacteria within the guts of individuals from industrialized societies compared to those of hunter-gatherers and non-industrialized farmers. This shift could lead to elevated levels of certain sex hormones in the bloodstream, posing serious health risks.

“We are still learning how the body reacts to this increased hormone recycling,” states Rebecca Britten from Jagiellonian University School of Medicine in Poland. “The implications could be significant.”

Sex hormones, like estrogen, circulate in the bloodstream. When levels rise excessively, a chemical marker attaches to liver cells, prompting hormone excretion through the intestines. That marker, a sugar molecule, serves as food for specific gut bacteria. These bacteria utilize an enzyme called β-glucuronidase to detach the marker.

Once freed from the marker, hormones can be reabsorbed by the body and reintroduced into the bloodstream. Research indicates that a considerable fraction of excreted sex hormones is recycled by gut bacteria in this manner.

In 2011, the term “oestrobolome” was introduced to describe the gut bacteria influencing estrogen metabolism and blood levels in both men and women. Earlier this year, the term “Testbolome” was coined to refer to gut bacteria affecting testosterone levels.

The latest research conducted by a British team analyzed the oestrobolomes of hundreds of individuals from 24 distinct populations worldwide. This included hunter-gatherers from Botswana and Nepal, rural farmers from Venezuela and Nepal, and urban residents from cities like Philadelphia and Colorado.

Britten’s team specifically assessed gene sequences that encode the enzyme beta-glucuronidase, examining both the overall proportion and diversity of these sequences. The results indicate that industrialized populations possess an estrogen recycling ability that is up to seven times greater and twice as diverse compared to hunter-gatherer and rural communities.

Moreover, the study found that formula-fed infants exhibit significantly higher recycling abilities—up to three times more likely and eleven times more diverse than breastfed infants. Interestingly, factors such as age, gender, and BMI showed no correlation with oestrobolome differences.

Researchers aim to determine if the observed gene sequences indicating higher recycling capabilities correspond with increased estrogen recycling in practice and, importantly, whether this leads to elevated blood estrogen levels. The body’s ability to adjust hormone levels could also play a role in offsetting this recycling.

If certain individuals maintain elevated estrogen levels due to their microbiome, this could notably impact fertility and overall health, potentially heightening cancer risks. Nonetheless, in specific scenarios, such heightened recycling could yield benefits. Britten emphasizes, “While increased estrogen recycling is often deemed harmful, that perception may not be accurate. For some with very low estrogen levels, this recycling may be advantageous.”

“This intriguing study contributes to the expanding evidence highlighting the significance of gut microbiome functionality in human health and development,” remarks Katherine Cook, a Wake Forest University School of Medicine professor studying the microbiome’s connection to breast cancer risk.

However, she notes limitations, such as the predominance of the industrialized population being US-based. “Including an additional European group could have enhanced the findings,” Cook adds.

Britten is keen to identify lifestyle factors influencing the observed differences and plans to conduct further research to gather comprehensive data.