Long-term psychological stress may also speed up changes linked to ageing in the body's immune system by disrupting healthy gut bacteria, according to a new study in Cell Stem Cell, a Cell Press journal, published recently.

Researchers from Sun Yat-sen University in Guangzhou, China, found that chronic stress in mice alters communication between the brain, intestine and bone marrow—the soft tissue inside the bones where blood cells are made. The changes reduced the number and function of haematopoietic stem cells, the master cells that produce all blood and immune cells, and lowered the production of lymphocytes, the white blood cells that help fight infections.

Human studies have already linked psychological stress to a higher risk of heart disease, diabetes, and weakened immunity. Scientists have long known that stress activates the body's "fight-or-flight" response, but exactly how signals from the brain reached the bone marrow remained unclear.

Using four different mouse models of chronic stress, the researchers tracked changes across the brain, gut and bone marrow. They found that stress reduced activity in two brain regions involved in emotional control and pain processing—the medial prefrontal cortex and the periaqueductal grey. This was followed by a significant drop in Lactobacillus reuteri, a helpful gut bacterium that keeps the right balance of microbes, and lower levels of spermidine, a natural compound that helps cells get rid of damaged material and stay healthy.

"Our research shows how areas of the brain that respond to stress control the balance of gut bacteria, which in turn affects how blood stem cells work," said senior author Meng Zhao.

"One surprising finding of our study was that suppression of only two specific brain regions was sufficient to produce many of the haematopoietic defects caused by psychological stress," added co-corresponding author Linjia Jiang.

"Alternations in the gut microbiota and in the microbial metabolite spermidine played a crucial role in mediating communication between the brain and the bone marrow," Jiang said.

The findings add to growing evidence from organisations such as the World Health Organization and the US National Institutes of Health that chronic stress affects both mental and physical health, including immune function. However, the researchers stressed that their work was conducted only in mice, meaning the same biological pathway still needs to be confirmed in humans.

"Although substantial work is needed before clinical translation, these findings provide a conceptual framework for developing new approaches to mitigate immune ageing and stress-associated immune dysfunction," Zhao said.

"More broadly, our findings raise the possibility that managing psychological stress may not only improve mental well-being but also help preserve immune function and promote healthy ageing," Jiang added.