London: Stomach problems at an early stage of life could cause depression later on, a new study led by an Indian-origin researcher suggests.

Dr Pankaj Pasricha and his team at Stanford University have found short-term digestive irritation such as irritable bowel syndrome could have massive implications for mental health later on.

"A lot of research has focused on understanding how the mind can influence the body. But this study suggests that it can be the other way around. Gastric irritation during the first few days of life may reset the brain into a permanently depressed state," a daily quoted Dr Pasricha as saying.

As not all stomach upsets lead to lifelong psychological problems the impact may depend on when it occurs during a person's development; it may also be related to their genetic makeup, say the researchers.

Dr Pasricha believes many patients date their gastrointestinal problems back to early childhood, before their psychological symptoms started. Therefore he suggests these digestive disturbances could cause mood disorders.

His theory has been bolstered by recent research that has linked depression and anxiety in humans to changes in the composition of gut bacteria. "The gut and the brain are hardwired together by the vagus nerve, which runs from the brain to the body's internal organs. The communication between the gut and the adult brain is elaborate and bi-directional, and changes in the gut are signalled directly to the brain," Dr Pasricha said.

To test their hypothesis they subjected 10-day-old laboratory rats to mild stomach irritation daily for six days.

"We hypothesised that this treatment might also be affecting the development of central nervous system, and driving the animals to anxiety and depression," he said.

Eight weeks later, the researchers found that the treated rats were far more likely than their peers to display depressed and anxious behaviours, including drinking less sugar water, less-active swimming and keeping to dark areas.

They also had increased levels of the stress hormones corticosterone and corticotrophin.

"It seems that when the rats are exposed to gastric irritation at the appropriate point in time. There is signalling across the gut to the brain that permanently alters its function," Dr Pasricha said.

The study has been published in the 'PLoS One' journal.

(Agencies)