For the past couple of decades, doctors and researchers have monitored rising colon cancer rates among young people with concern. In the United States, colorectal cancer rates increased by 3% every year among adults ages 20 to 49 between 2013 and 2022.
Researchers have suspected highly processed foods, toxins in the gut and sedentary lifestyles. Now there is a new suspect: microplastics.
A study released last month from researchers at Central South University in China found that long-term exposure to polystyrene nanoplastics – the plastic that is used in Styrofoam cups and containers – promoted tumour growth in mice that were genetically modified to be predisposed to colon cancer for research purposes.
The nanoplastics, researchers found, built up in the colon, disrupting the cells lining the gut and damaging the balance of gut bacteria. The mice exposed to nanoplastics had more tumours and more severe tumours than those that were not exposed.
The research joins a growing number of studies that have found hints that microplastics and nanoplastics could be contributing to the onset and progression of colorectal cancer.
A study published last year found more microplastics were concentrated in the tumours of patients with colorectal cancer compared with healthy nearby tissue.
“My intuition says it’s a major factor,” said Lorne Hofseth, professor and associate dean for research in the College of Pharmacy at University of South Carolina.
Part of the suspicion stems from the timing of the rise in colon cancers among young people. Epidemiologists began to identify the increase in the 1990s. Because colorectal cancers typically take around 20 years to develop from exposure to disease, researchers are looking for a risk factor that rose in the 1970s and continued into the present day. And because the increase is global, they are also looking for something that affects people around the world.
“Put all that together, certain factors bubble up,” Hofseth said. “There’s been a rise in consumption of ultra-processed foods. There’s been a rise in ‘forever chemicals’. There has been a rise in the synthetic food dyes. But there’s also been a rise in microplastics, a significant rise.”
In the US, early-onset colorectal cancer has been on a steady rise since the 1990s, with a steeper rise over the past few years. The recent spike is probably due to a change in screening guidelines in 2021, which advised beginning screening at age 45 instead of 50.
In many ways, young people today are healthier than they were generations ago, said Frank Frizelle, professor of surgery at the University of Otago in New Zealand.
Young people, he pointed out, ate less red meat and more vegetables, smoked less and drank less alcohol. But the increase in early-onset cancers persists.
Frizelle believes that microplastics may be contributing to the rise of colon cancer by disrupting the mucous layer, a protective barrier of fluid that keeps dangerous toxins and microbes from reaching the colon wall. The tiny shards of plastic may be penetrating the mucous layer – “like popping a hole in a condom,” he said – making it more likely that toxins can damage the colon.
Early-onset cancers are also more likely to involve the mucous layer of the colon than colon cancers in older people; at the same time, some animal studies have found that microplastics can damage the mucous layer.
“My own thoughts are that it’s going to prove not to be the microplastics themselves – microplastics are going to prove to be a way of getting through the mucous layer,” Frizelle said.
Researchers say that much more investigation is needed to draw a clear link between colorectal cancer and microplastics. But the available data is troubling.
One thing that is clear, however, is what to do about the problem in the meantime: earlier screenings of young people. Early screenings can remove precancerous polyps in the colon and rectum before they have a chance to develop into full-blown cancer.
In countries such as Austria, where screening starts at age 40 instead of 45 or 50, scientists don’t see a marked increase in early-onset cancer. In fact, rates are actually declining.
“Screening will be a way of managing the problem,” Frizelle said. But he also believes people need to start thinking about how to manage the large amounts of food exposed to plastic.
“With food, I do wonder if we need to think about things a little differently,” he added. “And just think about how we can reduce contamination in our food.”
One of the best ways to avoid exposure to microplastics is to not heat food or drinks in plastic containers, because this causes the chemicals to leach out at a higher rate.
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