But while the rates ofcolorectal cancerare declining overall, theyresteadily rising in people younger than 50.
To answer that question, researchers are turning to environmental factors.
There are likely many overlapping factors at play, but emerging research points to microplastics as a key suspect.
Photo Illustration by Michela Buttignol for Verywell Health; Getty Images.
Early-onset cancers started rising in adults born after 1950, around the time mass plastic consumption took off.
Plastics are now ubiquitous.
Theyrefound in kitchenware, clothes, toys, and countless other products that people interact with daily.
Were seeing epidemiological associations.
How Might Microplastics Contribute to Colorectal Cancer?
During the digestive process, bacteria release toxins into the gut.
Some foods, like alcohol, red meat, and processed foods, can increase toxin production.
The mucosa helps keep these toxins away from the intestinal walls and the rest of the body.
Typically, it takes decades for that incremental damage to lead to cancer development.
He explained that the mucus that lines the gut has two layers.
Its a bit like making tiny pinpricks in a condom, he says.
Once those holes exist, toxins can leach through and damage the intestines.
Microplastics themselves dont cause cancer.
If that model turns out to be wrong, there are plenty of other potential explanations.
The mucus layer is hydrophobic, meaning it attracts fat but repels the fluids that fill the intestine.
Plastics are also hydrophobic.
The gut also has a protective mechanism called the tight junctions.
Those are bonds between cells that keep toxins out while letting nutrients through.
Frizelle wonders, too, whether the size of the plastic bits matters.
Microplastics are less than 5 millimeters in size, or about the size of a pencil eraser.
Nanoplastics, meanwhile, are less than 1,000 nanometersthe size of a bacterium.
A healthy gut is teeming with beneficial bacteria and plenty of prebiotic fiber for it to consume.
We see dysbiosis associated with cancer.
We see some bacteria are carcinogenic.
And then we also see this microplastic exposure association with increasing incidence of cancer.
When you link all this together, there are clear correlations or associations, Jayakrishnan said.
One idea theyre investigating is whether microplastics can harbor cancer-causing bacteria.
If microplastics can push through the mucosal lining, they may even ferry those bacteria to the intestines.
Plastics themselves are chemically inactive.
They come in different sizes, shapes, chemical composition, and added-on chemicals.
These chemicals may mess with the balance of the gut microbiome.
But establishing causality is another task.
This model is harder to replicate with plastic exposure, Jayakrishnan explained.
This has been a lot of trial and error.
Research is about 20 failures to one success, Frizelle said.
He also compared the field with the revelation that smoking caused cancer.
This is new stuff, Frizelle said.
2024;386(6720):eadl2746.
