Discarded sex hormones can be re-entered into the bloodstream through the action of bacteria residing in the gut. A recent study has revealed a notable difference in the presence of these hormone-recycling bacteria: they are significantly more abundant in the digestive systems of individuals from industrialized societies compared to those living as hunter-gatherers or in non-industrial farming communities.
This discovery suggests a potential consequence of urban living: certain individuals may experience elevated levels of specific sex hormones circulating in their blood. Such an alteration could have profound implications for health.
Rebecca Brittain, a researcher at Jagiellonian University Medical College in Poland, stated, “We do not know how the body would respond to this increased input. However, the implications could be quite large.”
The Mechanism of Hormone Recycling
Sex hormones, like oestrogens, naturally circulate within the bloodstream. When their levels become excessively high, cells in the liver attach a chemical marker, a process that leads to the hormone’s excretion. This excretion often occurs via the gut. The marker itself is a sugar molecule, which serves as a food source for certain types of gut bacteria. These bacteria possess enzymes, known as beta-glucuronidases, capable of cleaving these sugar tags.
Upon removal of the tag, a hormone can be reabsorbed by the body and subsequently return to the bloodstream. Existing research indicates that a substantial proportion of excreted sex hormones are indeed recycled by gut bacteria through this mechanism.
Introducing the “Oestrobolome” and “Testobolome”
The concept of the “oestrobolome” was first introduced in 2011. It describes the collective group of gut bacteria that possess the capacity to modify oestrogens, thereby potentially influencing oestrogen levels in both men and women. More recently, the term “testobolome” has been proposed to denote gut bacteria that can affect testosterone levels.
Comparative Study of Oestrobolomes Across Populations
The latest study, conducted by Brittain’s team, undertook a comparison of the oestrobolomes of hundreds of individuals spanning 24 distinct global populations. This analysis utilized data from prior studies that had sequenced the gut microbiomes of these participants.
The study included diverse groups such as hunter-gatherers from Botswana and Nepal, rural farmers in Venezuela and Nepal, and urban inhabitants from Philadelphia and Colorado. The research focused on identifying genetic sequences that code for beta-glucuronidase enzymes. By measuring the overall proportion and diversity of these sequences, the team aimed to quantify the hormone-recycling capacity of gut microbes.
Key Findings: Industrial Societies Show Higher Recycling Capacity
The results indicated that the oestrogen-recycling capacity of gut microbes in industrialized populations is up to seven times greater than that observed in hunter-gathering and rural farming populations. Furthermore, the diversity of these microbes was found to be twice as high in the industrialized groups.
The research also revealed significant differences in infants. Babies fed formula exhibited up to three times the recycling capacity and up to eleven times the diversity of oestrogen-recycling microbes compared to breastfed infants. Interestingly, an individual’s age, sex, and Body Mass Index (BMI) did not appear to influence their oestrobolomes.
Implications and Future Research
Brittain’s team, along with other researchers, is now working to determine if the enhanced recycling capacity suggested by the genetic data actually correlates with increased oestrogen recycling and, most critically, whether this leads to elevated blood hormone levels. It is possible that the human body is capable of adjusting hormone levels to partially or fully compensate for higher recycling rates.
However, if certain individuals consistently maintain higher blood oestrogen levels throughout their lives due to their specific microbiomes, this could substantially impact their fertility and overall health. Potential consequences include an increased risk of certain cancers, although in some instances, these effects might prove beneficial. Brittain commented, “The assumption is usually that higher oestrogen recycling is harmful. I don’t think that’s a fair assumption. For some people with really low oestrogen levels this could be a good thing.”
Katherine Cook, a researcher at Wake Forest University School of Medicine in North Carolina who is investigating the links between the microbiome and breast cancer risk, described the study as “an interesting study that adds to the growing evidence of the importance of the gut microbiome function in human health and development.”
Cook also noted some limitations, specifically that all the industrialized populations studied were located in the US. She suggested that including additional cohorts, perhaps from Europe, could have strengthened the associations observed within industrialized societies.
Brittain stated that her team plans to identify the lifestyle factors that contribute to the observed differences. “We would love to know so much more about these individuals, but the data didn’t exist, so we’ll do our own study,” she concluded.