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Doctors and researchers are still trying to pinpoint how bowel cancer develops. Getty Images
  • Researchers presented a study this week that indicated certain types of gut bacteria may pose a greater risk of bowel cancer.
  • Humans have about 100 trillion microbes in their bodies, outnumbering their cells by a 10-to-1 margin.
  • Most bacteria in the microbiome are beneficial, but some can cause serious health issues.

People with specific kinds of bacteria in their gut may have a greater risk of getting bowel cancer.

Kaitlin Wade, PhD, a fellow from the University of Bristol in the United Kingdom, said Monday at the National Cancer Research Institute’s Cancer Conference in Glasgow that researchers had “found evidence that the presence of an unclassified type of bacteria from a bacterial group called Bacteroidales increased the risk of bowel cancer by between 2 and 15 percent.”

This research was the first study using Mendelian randomization, a technique the Centers for Disease Control and Prevention (CDC) says uses measured variation in genes of known function to examine the causal effect of a modifiable exposure on disease in observational studies.

“It is a very significant study because there is a rapid increase in young people with colon cancer, and the exact reason is unknown,” Anton Bilchik, MD, PhD, MBA, FACS, chief of gastrointestinal research and chief of medicine at John Wayne Cancer Institute in Santa Monica, California, told Healthline.

“This provides a potential mechanism to further study and potentially identify and treat,” he said.

Wade said the study confirmed previous research suggesting Bacteroidales bacteria is more likely to be present, and in larger quantities, in people with bowel cancer.

Humans are mostly microbes — more than 100 trillion of them in a human body.

They outnumber our cells 10 to 1, and most of them live in our gastrointestinal tract, also known as the gut.

The microbiome is the genetic material of all the microbes in the human body, including bacteria, viruses, protozoa, and fungi. It can weigh as much as 5 pounds, according to the Center for Ecogenetics and Environmental Health at the University of Washington.

Most of those bacteria are beneficial. They help humans digest food, regulate the immune system, and protect against other bacteria that cause disease.

Bacteria also produce B vitamins such as B-12, riboflavin, and thiamine. They also produce vitamin K, which is necessary for blood coagulation.

“There are literally trillions of bacteria in our gut and many new species will be discovered,” Dr. William Li, author of “Eat to Beat Disease: The New Science of How Your Body Can Heal Itself,” told Healthline.

“The links between gut bacteria and cancer tell us we need to be even more alert to potential disturbances that our diet can cause to our beneficial bacteria, and to the potential for stoking the growth of harmful bacteria,” he continued.

The microbiome wasn’t generally recognized until the late 1990s. It’s unique to each person and is determined by genetic makeup and environment.

It also remains relatively stable over the course of someone’s life, unless affected by things such as antibiotics, illness, and dietary changes.

Wade said studies involving humans and mice have shown the connection between bowel cancer and the gut microbiome.

However, it wasn’t clear whether components of the gut microbiome caused bowel cancer, whether the cancer lead to the variation in the gut, or whether other factors caused the association.

The Mendelian randomization for the project analyzed data from thousands of people in multiple studies to answer those questions.

Wade said the findings need to be replicated in other studies using different sets of data and methods before the implication can be fully understood.

She said the exact strain or species of bacteria in the Bacteroidales group needs to be classified.

Even if the bacteria cause cancer, more work is needed, as researchers don’t know whether trying to alter them might have other unforeseen effects in the human body.

“However, I believe that we are at the forefront of understanding and appreciating the complexity of these relationships — not only those between the human gut microbe and disease, but also between human genetic variation and the gut microbiome itself, which is required to appropriately use these methods to appraise causality,” said Wade.

Ian Tomlinson, the incoming director of the Cancer Research UK Edinburgh Centre, praised the study in a statement, but said it’s too early to draw definite conclusions.

“Nevertheless, similar larger studies have the potential for greatly improving our understanding of how bowel cancer develops,” he said.