Does IBD play a role in cognitive decline? What a 2026 systematic review of 66 studies actually says

Ulcerative colitis and Crohn's disease — the two main forms of inflammatory bowel disease — are long-term conditions where parts of the digestive system become inflamed [1][2]. People living with them know the disease doesn't only stay in the gut. Fatigue. Mood. Sleep. And, for a lot of people, the harder-to-name feeling that your thinking has gone slightly out of focus.

That last one — the lost word, the doubled-back paragraph, the meeting you walked out of and immediately couldn't recall — has had a name in the community for a long time. "Brain fog" is what people call it. Whether the research actually backs up what people feel is a separate question, and a 2026 paper in the Journal of Crohn's and Colitis sat with that question for a while.

What the review actually did

It is a systematic review, conducted to PRISMA standards, of studies that looked at cognitive function in people with IBD. The authors searched PubMed and Scopus from each database's inception through 30 August 2024, and ended up with 66 included studies: 31 population studies, 13 genetics studies (including Mendelian Randomization and Genome-Wide Association Studies), and 22 preclinical studies in laboratory and animal models [3].

A note on what those categories mean, because it matters for how much weight to put on the headline:

• Population studies look at large groups of people and ask whether having IBD is statistically linked to scoring lower on tests of memory, attention, or processing.
• Genetics studies like Mendelian Randomization use inherited genetic variants as a natural "experiment" to probe whether the link between IBD and cognition is likely causal rather than just shared with other factors.
• Preclinical studies are mostly mice and cell models. They are good for mechanism — how inflammation in the gut could plausibly reach the brain — but they do not, on their own, prove anything about a specific person.

Adding up all three lines of evidence is the point of doing a systematic review.

What it found

The review reports that people with IBD may show impaired cognitive function, particularly in memory, attention, and executive processing, and that disease activity, chronic inflammation, and psychological stress appear to be the main contributors to those deficits [4]. The overall conclusion the authors are willing to commit to is that IBD is associated with cognitive impairment and an increased risk of dementia — with the deliberate, careful word associated doing real work in that sentence [5].

They also flag a more hopeful, more tentative thread in the data: some IBD treatments, particularly biologics, may mitigate neuroinflammation-related cognitive decline. Importantly, the authors do not present this as established. They frame it as something that needs longer follow-up studies and randomized clinical trials before anyone can claim a neuroprotective role for any specific therapy [6].

Why "associated" is the load-bearing word

A systematic review summarises the studies it found, and most of the studies it found here are observational. Observational designs are good at saying "these two things tend to show up together"; they are not, on their own, good at saying "this one causes that one". Add in mixed results across populations, ages and methods — the authors describe the underlying evidence as "controversial" in places, and the mechanisms as "poorly understood" — and the only honest summary is the one the paper itself prints [5].

So: there is a real signal. People with IBD do appear, as a group, to score worse on some cognitive measures than people without IBD, and there are several biologically plausible reasons why (chronic inflammation, a gut–brain axis under stress, sleep loss, pain, the cumulative weight of a hard chronic illness). What there is not, yet, is a clean causal story, a number you can put on individual risk, or a treatment plan built around protecting cognition specifically.

What this means in everyday life

A few useful things to take from a paper like this without overreading it.

First, brain fog in IBD is not in your head as a moral failing. The literature now describes the same pattern many people in the community have reported for years, and it sits inside a recognisable cluster — disease activity, inflammation, stress — rather than appearing out of nowhere. That alone is worth saying out loud.

Second, this is not a diagnostic tool. The review is about groups of people studied together, not about you individually. A cognitive test result, a forgetful week, or a hard flare do not by themselves tell you anything about your dementia risk. The categories at the population level and the experience at the individual level are not the same thing.

Third, the most useful response is the ordinary one. If thinking feels foggier than it used to — during flares, between flares, or with no pattern at all — that is worth mentioning to your IBD team or your GP, the same way you would mention persistent pain, low mood or unexplained weight change. They have your history; we don't. We can make the research legible; only your clinician can interpret it against the rest of you.

This is the part where, as a curator, we step back. The honest takeaway from a 2026 systematic review of 66 studies is not a slogan. It is a sentence with a careful word in the middle of it: IBD is associated with cognitive impairment and an increased dementia risk, and the people who study this for a living think there's enough signal here to keep looking. Holding that sentence as it is — without flattening either side — is part of how we earn trust with health information.