For some time doctors have known that psychological therapies can reduce the symptoms of irritable bowel syndrome in the short term.

IBS is a gastrointestinal disorder that affects 7 -- 16 percent of the U.S. population, adding somewhere between $950 million to $1.35 billion annually to the nation's healthcare bill.

A new meta-analysis, published online on Dec. 22, 2015 by the journal Clinical Gastroenterology and Hepatology, has now found that the beneficial effects of psychological therapy also appear to last at least six to 12 months after the therapy has concluded. The study analyzed the results of 41 clinical trials from a number of different countries containing more than 2,200 patients.

"Our study is the first one that has looked at long-term effects," said senior author Lynn S. Walker, professor of pediatrics at Vanderbilt University Medical Center. "We found that the moderate benefit that psychological therapies confer in the short term continue over the long term. This is significant because IBS is a chronic, intermittent condition for which there is no good medical treatment."

IBS, which is characterized by chronic abdominal pain, discomfort, bloating, diarrhea or constipation, is classified as a disorder of the "brain-gut axis." Although no cure is known, there are treatments to relieve symptoms including dietary adjustments, medication and psychological interventions.

"Western medicine often conceptualizes the mind as separate from the body, but IBS is a perfect example of how the two are connected," said first author Kelsey Laird, a doctoral student in Vanderbilt's clinical psychology program. "Gastrointestinal symptoms can increase stress and anxiety, which can increase the severity of the symptoms. This is a vicious cycle that psychological treatment can help break."

The studies that Laird analyzed included a number of different types of psychological therapies, including cognitive therapies, relaxation and hypnosis. Her analysis found no significant difference in the effectiveness of different types of psychotherapy. It also found that the length of the treatment (the number of sessions) didn't matter.

Possibly most significant from a healthcare cost perspective was the finding that treatments conducted online appear to be equally as effective as those conducted in person.

"In this study we looked at the effect of psychological therapies on gastrointestinal symptoms. In a follow-up study I am investigating the effect that they have on patients' ability to function: go to work, go to school, participate in social activities and so on," Laird said.