Chronic stress can disrupt gut bacteria and accelerate the progression of colorectal cancer, according to a new study that researchers say also suggests that gut-friendly bacteria could play a role in treatment.

The study’s results, set to be presented on Sunday at a scientific meeting of the United European Gastroenterology in Vienna, Austria, indicate that chronic stress promotes the progression of colorectal cancer by reducing intestinal Lactobacillus bacteria.

Multiple studies in the past have established an association between chronic stress and the spread of tumour cells, including the progression of colorectal cancer. But the role of gut microbes in this process has remained unclear.

Qing Li and her colleagues at the West China Hospital, Sichuan, have now found that chronic stress increased tumour growth as well as reduced at least three species of gut bacteria — Lactobacillus johnsonii, Lactobacillus gasseri and Lactobacillus plantarum. The researchers observed that the greater the tumour numbers, the fewer the bacteria which, they say, are essential for an effective immune response against cancer.

“Stress-linked colorectal cancer progression can be attributed to a reduction in these beneficial gut bacteria as this weakens the body’s immune response against cancer,” Li said in a media release issued by UEP, a professional association of digestive health experts. The researchers supplemented mice during chronic stress with Lactobacillus and observed reduced tumour formation.

“Through faecal analysis, we found that Lactobacillus plantarum specifically regulated bile acid metabolism and enhanced the function of CD8+ T cells,” Li said. CD8+ T cells are a type of white blood cells that play a key role in anti-tumour immune responses.

The findings indicate how Lactobacillus might enhance anti-tumour immunity, Li said. “Combining anti-tumour drugs with Lactobacillus plantarum supplementation could be a (possible) therapeutic strategy for patients with stress-related colorectal cancer,” she said.

India’s cancer registry datasets show that colorectal cancer incidence rates are rising in the country, from 5.8 per 100,000 people in 2005 to 6.9 per 100,000 by 2014 to 15.2 per 100,000 by 2021. Health experts have attributed this rise to a shift towards a calorie-rich and low-fibre diet, among other factors.

In the next phase of their research, Li and her colleagues plan to collect tumour and faecal samples from patients with colorectal cancer and analyse changes in their gut microbes in relation to possible chronic stress.

“Our goal is to verify whether Lactobacillus plantarum is significantly reduced in colorectal cancer patients who are also stressed and explore its relationship with anti-tumour immune cells,” Li said. “Restoring beneficial bacteria in the gut could strengthen the body’s natural defences against colorectal cancer.”