What is already known
Infertility affects about 186 million people worldwide, and high rates of infertility may be a problem in countries experiencing a rapid aging population. Alterations in gut microbiota composition have been associated with infertility, but a causal link hasn’t been found yet.
What this research adds
Researchers assessed whether genetic factors involved in shaping the gut microbiota may influence the risk of infertility. The team identified several bacteria linked to a low risk of infertility in men and women, as well as one bacterial genus associated with a high risk of male infertility and one bacterial family associated with a high risk of female infertility..
Conclusions
The findings suggest that there is a causal link between the gut microbiota and infertility.
Infertility affects about 186 million people worldwide, and high rates of infertility may be a problem in countries experiencing a rapid aging population. By looking at genetic differences that affect the composition of the gut microbiota, researchers have now identified bacteria associated with a high risk of infertility in men and women.
The findings, published in Scientific Reports, may provide insights into early diagnosis, prevention and treatment of infertility.
The condition has been associated with alterations in gut microbiota composition, but a causal relationship hasn’t been found yet. “Despite some observational epidemiological studies that have indicated a potential relationship between gut microbiota and male infertility, confirming a causal link through such studies remains challenging,” the researchers say.
The team, led by Taozhi Li at the China Academy of Chinese Medical Sciences in Beijing, used an approach called Mendelian randomization to assess how genetic factors involved in shaping the gut microbiota may influence the risk of infertility.
Genetic data
The researchers used data from a study that revealed the genetic variants influencing the composition of the human gut microbiota in more than 18,000 people from various countries, including the USA, Israel, South Korea, Germany and the UK. Most people were of European descent and the age of participants ranged from 50 to 62 years.
To investigate the impact of host genetics on the diversity of gut bacteria, only the bacterial taxa present in more than 10% of the samples were included in the analysis.
The genetic data relevant to infertility came from the FinnGen study, which combines genome information from samples collected by a network of Finnish biobanks with digital health care data from national health registries. The dataset included samples from 994 infertile men and about 100,000 controls, and 9,831 infertile women and nearly 94,400 controls.
Causal link
The researchers identified 6 bacterial taxa that may be involved in male infertility. Among these, 5 taxa — including family.Bacteroidaceae.id.917, genus.Bacteroides.id.918 and order.Enterobacteriales.id.3468 — may have a protective role against male infertility. Instead, genus.Allisonella.id.2174 was associated with a high risk of infertility in men.
The team also identified 11 bacterial taxa that may be involved in female infertility: genus.Faecalibacterium.id.2057 was associated with a high risk of infertility in women, whereas the other 10 — including genus.Ruminococcustorquesgroup.id.14377, genus.Desulfovibrio.id.3173 and order.Bifidobacteriales.id.432 — may have a protective role against female infertility.
“Our analysis yielded conclusive findings regarding the causal associations between gut microbiota and infertility at various taxonomic levels,” the researchers say. However, they add, the underlying mechanisms remain unknown. “There is still a paucity of relevant [randomized clinical trials] investigating the specific relationship between gut microbiota and infertility, mainly due to the complex interactions between the host and gut microbiota.”
