Depression in inflammatory bowel disease: risk factor, prodrome or extraintestinal manifestation?

We read with interest Frolkis and colleagues' recent study, in which depression was associated with increased risk of incident IBD in a large primary care database.1 While treatment of depression in IBD has been suggested to improve IBD outcomes,2 this study goes further, suggesting that assertive pharmacological treatment of depression could reduce the incidence of IBD altogether.

Despite the study's manifest strengths, we wish to draw the authors' attention to an important limitation of its current design that tempers its conclusions. Temporality between exposure and outcome is a key test of causality.3 This is challenging in the context of depression and IBD because their symptoms frequently overlap. For example, 40% to 80% of patients with established IBD experience significant levels of fatigue and sleep disturbance,4 and such symptoms frequently arise during the prodromal period prior to IBD onset.5 Although the authors...

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