As individuals who suffer from chronic medical illnesses are acutely aware, living with such diseases can be remarkably disruptive and stressful1. For instance, irritable bowel syndrome (IBS), which affects approximately 11% of the world population2, causes chronic abdominal pain and "altered bowel habit" (i.e., diarrhea, constipation, or both)3-4, resulting in thousands of dollars of expenses for patients every year5.
Given these complications, it's perhaps not surprising then that IBS and other chronic diseases are associated with an increased chance of developing a mental disorder, such as anxiety or depression6-8. Living with the physical burden of IBS with the added financial stresses of trying to treat this disease can be overwhelming for patients, leading to excessive worrying and feelings of hopelessness.
More recently, though, researchers have begun to realize that this effect may go both ways. Not only can chronic illnesses such as IBS lead to increased anxiety and depression, anxiety and depression may actually worsen the effects of such diseases9-10. In the case of IBS, individuals with comorbid (i.e., co-occurring) anxiety and depression experience their symptoms for a longer period of time than individuals without the associated mental disorders11-12. Though scientists are still investigating this effect, one reason this relationship might exist is due to the connection between the central nervous system (CNS), which includes the brain and spinal cord, and what is called the enteric nervous system (ENS), which controls the gastrointestinal system (e.g., stomach, colon)13-14. Because communication between these two systems appears to be bidirectional, it is possible that anxiety and depression can affect the gastrointestinal system directly.
In this regard, a looming question becomes: can anxiety and depression actually cause or increase one's chances for developing IBS? In a recent paper15, Alice Sibelli, a PhD student at King's College London, and her colleagues attempted to answer this very question. Specifically, they were interested in whether anxiety and depression increase one's chances for developing IBS and, if so, how much do they increase this risk? Given that these disorders are often comorbid, these questions are difficult to answer.
For instance, if a person has IBS and anxiety, it could be that the anxiety developed as a result of IBS, that IBS developed as a result of anxiety, or that the two are completely unrelated. Thus, for their investigation, the researchers used an approach known as a meta-analysis. Whereas a typical study may examine only 100 participants, meta-analyses combine data from upwards of hundreds of studies, sometimes including thousands of individual participants, into a single analysis. This approach allows researchers to take into account differences across a number of studies, helping them to understand the nuances of a particular effect.
For their meta-analysis, Sibelli and colleagues found that, across 11 studies, anxiety and depression were significant risk factors for IBS – doubling the chance that an individual developed the disorder. This effect seemed to be even stronger for individuals previously diagnosed with a gastrointestinal infection, which in and of itself increases the risk for developing IBS. Thus, these findings provide evidence that anxiety and depression could contribute to the development of IBS.
There are two important factors to consider, though. First, given the overlap between anxiety and depression, it could be that the increased risk is due to general psychological distress – and not specifically anxiety or depression. In other words, simply being more stressed could increase your chances of developing IBS. Second, given that the studies involved were correlational, it's unclear whether this stress directly influences the development of IBS or whether it does so through other means. For instance, it could be that individuals chronically high in stress are more likely to eat foods that can irritate the lining of the gastrointestinal tract, leading to the development of IBS.
Regardless, though, these findings highlight the important role that psychological stress can play in chronic medical diseases such as IBS, which many typically think of as purely physical in nature. The knowledge gained from this current work can help doctors identify patients who might be at particular risk for developing IBS and may help guide treatment. Specifically, it could be that targeting symptoms of anxiety and depression may help alleviate the symptoms of IBS in some patients.
Date of original publication: October 12, 2016.
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