Theories abound about the cause of Irritable Bowel Disease (IBD): Diet? Stress? Perhaps an infection?

On the other hand, is it possible depression could be triggering the disease in some of the 20 per cent of Canadians suffering from this digestive system disorder?

New research conducted by scientists in McMaster University's Intestinal Disease Research Program suggests it's highly likely that in some patients depression is wreaking havoc on the gut. Their research appears in today's online edition of The Journal of Clinical Investigation.

"The gut is intimately connected to the brain, more than any other organ in the body. In fact, the gut contains more nerves than the spinal cord," said Jean-Eric Ghia, lead researcher and a post-doctoral fellow in McMaster's program.

Ghia and his colleagues evaluated mice which had been induced with depressive-like behaviours, then continued to follow them after the animals had been given anti-depressants. The experiment illustrated how the nervous system influences inflammation in the gut.

"Our study shows that depression increases susceptibility to inflammation, and anti-depressant therapies improve not only the depression but also the inflammation in the gut," he said.

The researchers also demonstrated that the vagus nerve - which starts in the brain stem and extends to the gastrointestinal tract - protects against inflammation by releasing nicotine. "In the absence of this nerve, the anti-depressant therapy does not improve inflammation in the gut, suggesting that this nerve is a major link between the brain and the gut," Ghia said.

For patients, he said the findings are significant: They illustrate the close relationship between depression and IBD and indicate selected depressed patients with IBD might benefit from novel treatment strategies, such as anti-depressants, the use of highly selective nicotinic stimulant (nicotinic receptors are found in the autonomic nervous system) or nerve stimulation.

McMaster University, a world-renowned, research-intensive university, fosters a culture of innovation, and a commitment to discovery and learning in teaching, research and scholarship. Based in Hamilton, the University, one of only four Canadian universities to be listed on the Top 100 universities in the world, has a student population of more than 23,000, and an alumni population of more than 131,000 in 128 countries.

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