In a new study, researchers found people who have a certain type of bacteria in their guts may be at greater risk of developing bowel cancer.
They found that the presence of an unclassified type of bacteria from a bacterial group called Bacteroidales could increase the risk of bowel cancer by between 2-15%.
This means that, on average, people with this type of bacteria within their gut may have a slightly higher risk of bowel cancer compared to those who don’t.
This the first study using a technique called Mendelian randomization to examine the causal role played by bacteria in the development of bowel cancer.
The findings support previous studies that have shown that Bacteroidales bacteria are more likely to be present, and in larger quantities, in individuals with bowel cancer compared to those without the disease.
The research was conducted by a team from the University of Bristol and elsewhere.
The microbiome is a community of microorganisms, bacteria in this case, that occur naturally in the body.
There is increasing evidence that the make-up of the microbiome plays a role in human health and the body’s susceptibility to disease.
The human gut microbiome, which contains approximately three trillion bacteria, aids digestion and provides protection against infections.
It is determined by a person’s individual genetic makeup and their environment, so is unique to each person.
It also remains relatively stable across a person’s life, unless it is affected by antibiotics, an illness or a change of diet, among other things.
The new method Mendelian randomization uses complex statistical analysis of data from large populations to provide evidence for cause and effect, rather than just the existence of an association.
With Mendelian randomization, the team used people’s natural, randomly inherited genetic variations, which alter levels of bacteria within the gut microbiome in a way that mimics a randomized trial, to see whether people with different genetic makeup and therefore different gut microbiome profiles have a different risk of colorectal cancer.
In this way, they don’t have to edit anyone’s gut microbiome directly by giving antibiotics or probiotics in a randomized trial or waste time waiting to see whether people within the population get colorectal cancer.
The researchers used data from 3,890 people taking part in the Flemish Gut Flora Project, the German Food Chain Plus study and the PopGen study, and 120,328 people in the international Genetics and Epidemiology of Colorectal Cancer Consortium.
They found that genetic variation in the population in particular parts of the genome were linked to the presence of varying amounts of 13 types of gut bacteria and that people with an unclassified type of bacteria from the Bacteroidales group had a higher risk of bowel cancer compared to people who did not have these bacteria.
The findings need to be replicated by other studies using different sets of data and methods before the implications for human health could be fully understood.
This is one of the first studies to use the methods to provide insights into the reasons for the postulated and plausible—but largely unproven—links between the microbiome and bowel cancer.
One author of the study is Dr. Kaitlin Wade.
The study was presented at the 2019 NCRI Cancer Conference.
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