A groundbreaking new study has demonstrated that the mix of microbes present in semen, known as the semen microbiome, plays an important role in male fertility. Researchers found that men with unexplained infertility tend to have dysbiosis, an imbalance in these microbes, compared to fertile men. These findings open exciting new possibilities for understanding, diagnosing, and even treating male infertility.
Dysbiosis in semen microbiome linked to reduced fertility
The study, published this week in the journal Nature Communications, analyzed semen samples from 200 couples struggling with unexplained infertility at a Boston fertility clinic. Using gene sequencing technology, the research team mapped out the microbial composition of the semen and compared it to that of 50 known fertile men.
They discovered that men in infertile couples had reduced microbial diversity in their semen and an overabundance of certain bacteria like Fusobacterium and Prevotella species compared to fertile men.
“It seems this dysbiosis, or imbalance in the microbes that are supposed to be there, can negatively impact sperm function and reduce fertility,” said lead researcher Dr. Sarah Nosrati.
Microbes may affect sperm motility and other parameters
The study also uncovered clues about how the semen microbiome interacts with sperm cells. Dysbiosis was associated with reduced sperm motility and more sperm DNA fragmentation compared to men with balanced microbiota.
“We found certain microbial byproducts can actually penetrate sperm cells and damage their DNA integrity. Other bacteria seem toimpede sperm cells’ ability to move properly,” said Nosrati.
Altered microbial profiles also corresponded to changes in infection-fighting immune cells in the semen. This indicates the relationship between bacteria and immunity is important for supporting healthy sperm development.
Diagnostic and therapeutic possibilities
Up until recently, semen was thought to be sterile. This study provides robust evidence that microbial residents play indispensible roles. The findings open doors for new infertility investigations and treatments.
“Now that we know the semen microbiome is involved, we can start asking whether we can modify it to promote fertility in afflicted men,” said Nosrati. Analyzing the bacterial composition of patients’ semen could also aid infertility diagnoses. Currently 30% of cases have no identifiable cause.
Researchers next plan to explore whether dysbiosis causes infertility directly or results from upstream reproductive issues. Larger clinical trials testing fecal transplants to rebalance the semen microbiome will also ensue.
Microbiome adds to picture of declining sperm health
Nosrati’s findings provide another piece in the complex puzzle of declining sperm counts and sperm health among Western men.
Sperm counts have plunged by over 50% in the last 40 years. At the same time, rates of testicular cancer and genital birth defects have risen. The causes behind these trends remain murky, although experts believe factors like pollution, smoking, and obesity may all play a role.
This study suggests there may be more to the sperm crisis than just environmental and lifestyle impacts. The testicular and reproductive microbiomes could fundamentally influence men’s fertility in ways we are only beginning to grasp. Integrating microbiome health into male reproductive medicine could open new avenues to combat this public health issue affecting 1 in 6 couples.
Global sperm count declines
|Decline in sperm count
|Decline in sperm quality
Data from Levine et al. Temporal trends in sperm count: a systematic review and meta-regression analysis. Human Reproduction Update, 2017.
Looking ahead at the fertility microbiome
As the first study conclusively demonstrating the impact of semen microbes on fertility outcomes, Nosrati et al.’s work represents an exciting step forward in male reproductive science after decades of focus solely on females.
However, the causes, implications, and potential solutions related to dysbiosis of the semen microbiome are still in early days of exploration.
“This opens up entire new avenues for research. But there is still much to investigate about this newly discovered microbial community before we can translate findings into medical practice,” said Dr. Petra Mårdh, head of andrology at Stockholm South Hospital not involved in the study.
Indeed, important questions remain about how aging, sexual habits, chronic illnesses or medications may impact the ecology of microbes in semen and reproductive organs.
More research discerning how modifiable factors like diet, stress levels, or exercise regimen interact with the fertility microbiome is critical. Clinical testing modes to characterize each man’s semen microbiome need development as well.
Nonetheless, these revelations regarding complex microbial-immune-reproductive interrelationships represent an exciting frontier with real promise for illuminating the root causes and future management of male infertility.
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