What happens in the gut doesn’t always stay in the gut. A recent study from the University of Southern California finds that inflammatory bowel disease (IBD) has a bidirectional relationship with depression. People with IBD are nine times more likely to also develop depression than people without IBD. Vice versa, people diagnosed with depression were more likely to have IBD later in life.
“This research reveals a clinical overlap between both conditions, and is the first study to investigate the two-way association between IBD and depression in siblings,” says Bing Zhang, MD, a gastroenterologist with Keck Medicine and co-lead study author in a statement.
IBD causes inflammation of the digestive tract in an estimated 1.6 million Americans. About 16 million Americans battle depression.
The research team studied the data of more than 20 million people from Taiwan’s National Health Insurance Research database, which has medical information on over 99% of Taiwanese residents. People with either an IBD or depression diagnosis and their siblings (with none of the conditions) were tracked for 11 years. They compared their health information to a control group of people without either condition but had similar age, sex, and socioeconomic status.
Not only did an IBD diagnosis increase the risk of depression nine-fold, but the sibling of a person with IBD was also almost two times as likely to develop depression. People with depression had a twice-as-likely risk of developing IBD. Their siblings without depression had a one-and-a-half times risk for it.
“The finding that people with IBD are more prone to depression makes sense because IBD causes constant gastrointestinal symptoms that can be very disruptive to a patient’s life,” explains Zhang. “And the elevated depression risk among siblings of IBD patients may reflect caregiver fatigue if the siblings have a role in caring for the patient.”
One surprising finding was the high likelihood of someone with IBD later developing depression. Dr. Zhang hypothesizes that this effect could stem from the gut’s close relationship with the brain. He speculates that inflammation in the brain, a contributor to depression, may stem from the GI tract.
While the researchers do not completely understand why siblings without the diseases have an increased risk for IBD or depression, they theorize it could come from genetic susceptibility to disease.
The study is published in the Journal of Gastroenterology and Hepatology.