Microplastics could increase bowel cancer and depression risk

Microplastics from food packaging may damage the gut and raise the risk of bowel cancer and depression, new research suggests.

Austrian researchers made the discovery after examining stool tissue from healthy volunteers and found that the tiny particles could alter microbial activity in the gut, with some of the changes reflecting patterns previously linked with depression and bowel cancer.

Experts described the findings as “significant” and said it was the first human study to show that these plastic fragments could alter the human gut microbiome – the community of microorganisms that live in the digestive system.

Researchers from the University of Graz used stool samples from five healthy volunteers to grow gut microbiome cultures, which were then exposed to five common microplastic types – polystyrene, polypropylene, low-density polyethylene, poly(methyl methacrylate) and polyethylene terephthalate.

All samples were tested at concentrations reflecting estimated human exposure, as well as higher doses to explore possible dose-dependent effects.

Microplastics are plastic fragments as small as two micrometres – around two-thousandths of a millimetre – which enter food, water supplies and even the air as plastics degrade naturally.

Recent studies have identified microplastics in human lung tissue, maternal and foetal placental tissue, human breast milk and human blood. A growing body of research has also linked them to cancer, heart disease, dementia and lower-quality sperm.

“These findings are significant given how pervasive microplastic exposure is in everyday life,” said Christian Pacher-Deutsch, a microplastics researcher at the University of Graz and lead author of the study.

“Microplastics have been found in fish, salt, bottled water, and even tap water, meaning that most people are exposed daily through ingestion, inhalation and skin contact.

“The key takeaway is that microplastics do have an impact on our microbiome.

While it’s too early to make definitive health claims, the microbiome plays a central role in many aspects of well-being, from digestion to mental health.

“Reducing microplastic exposure where possible is therefore a wise and important precaution.”

Although total bacterial cell counts remained largely unchanged, microplastic-treated samples showed a consistent and significant increase in acidity compared with untreated ones, indicating altered microbial activity.

Further analysis showed that certain bacterial groups changed in composition depending on the microplastic type, with most changes occurring within the phylum Bacillota – a key group of gut bacteria important for digestion and overall gut health.

The researchers also discovered that some of these microplastic-related changes mirrored microbial patterns previously linked to diseases such as depression and bowel cancer.

Scientists said they were not yet certain why this occurred but suggested several possible explanations.

“For instance, biofilms can form on microplastic surfaces, providing new niches that some microbes colonise more rapidly,” said Mr Pacher-Deutsch.

“Microplastics may also carry chemical substances that directly influence bacterial metabolism.

“This can lead to changes in acid production, which may serve as a bacterial stress response, unintentionally altering the gut’s pH.”

The research will be presented in full at the United European Gastroenterology annual congress in Berlin on 7 October.

There are around 44,000 cases of bowel cancer every year in the UK and 142,000 in the US, making it the fourth most common cancer in both countries.

Symptoms often include changes in bowel movements such as persistent diarrhoea or constipation, feeling the need to poo more or less frequently and blood in the stool. Stomach pain, bloating, a lump in the abdomen, fatigue and unexplained weight loss are among other signs.

Although the vast majority of bowel cancer diagnoses affect those aged over 50, rates in younger adults have risen by about 50 per cent over the past 30 years, while figures in older age groups have remained stable or declined.

Cancer Research UK estimates that over half (54 per cent) of bowel cancer cases in the UK are preventable.