Microplastics Disrupt Gut Bacteria Linked to Cancer and Depression

A recent study has revealed that microplastics can significantly alter the human gut microbiome, raising concerns about their potential health impacts. Conducted by the Center for Biomarker Research in Medicine in Austria, this research was presented at the United European Gastroenterology Week on October 6, 2025. This study marks a pivotal examination of how various microplastics, defined as plastic particles smaller than 5mm, can influence gut health.

The findings emphasize the pervasive nature of microplastics, which have been detected in diverse environments globally, from the peaks of Mt. Everest to the depths of the Mariana Trench. Alarmingly, microplastics have also been discovered in human tissues, including blood and heart. Research suggests that an average person may ingest between 78,000 and 211,000 microplastic particles annually through food, beverages, and air.

Researchers explored the effects of five common types of microplastics—polystyrene, polypropylene, low-density polyethylene, polyvinyl chloride, and polyethylene terephthalate—on gut microbiome cultures derived from stool samples of five healthy volunteers. The study employed a range of microplastic concentrations, simulating both typical human exposure levels and higher doses to assess potential dose-dependent effects.

Although total bacterial cell counts remained stable across all cultures, the presence of microplastics was associated with a notable decrease in pH levels compared to controls. This suggested changes in bacterial metabolism. Furthermore, specific alterations in the bacterial composition were observed, with particular groups either flourishing or declining based on the type of microplastic introduced. Key families affected included Lachnospiraceae, Oscillospiraceae, Enterobacteriaceae, and Ruminococcaceae. Most changes occurred within the phylum Bacillota, which plays a crucial role in digestion and overall gut health.

The shifts in bacterial populations led to concurrent changes in metabolic products, influencing the production of important compounds such as valeric acid, 5-aminopentanoic acid, lysine, and lactic acid. Researchers posit that microplastics may contain chemicals that interfere with bacterial metabolic processes, prompting bacteria to alter their acid production as a stress response. This unintended consequence can further disrupt gut pH and the overall balance of the microbiome.

Lead author Christian Pacher-Deutsch noted, “At this stage, the exact pathways remain unclear, but several plausible explanations are emerging. Microplastics may change microbial composition by creating physical or chemical environments that favor certain bacteria. For instance, biofilms can form on microplastic surfaces, providing new niches that some microbes colonize more rapidly.”

The implications of these findings are significant, as alterations in the gut microbiome could potentially increase the risk of various diseases. Notably, the changes observed in the study mirrored patterns associated with conditions such as depression and colorectal cancer. This body of evidence underscores the possibility that our increasingly plastic-dominated environments may have unforeseen and serious consequences for human health.

As research continues to uncover the complexities of microplastics and their effects on health, this study highlights the urgent need to address plastic pollution and its implications for public health.