People with inflammatory bowel disease (IBD) are more than twice as likely to develop dementia than their peers, suggesting chronic inflammation may play a role.
We are increasingly seeing evidence of a link between our digestion and cognition, known as the gut-brain axis. However, the exact interplay between the two is still unclear.
Recent studies have linked systemic inflammation with the types of neurological changes seen in Alzheimer’s disease, and this prompted Dr Mu-Hong Chen, a psychiatrist at Taipei Veterans General Hospital in Taiwan, to investigate whether chronic gut inflammation had a similar role in dementia.
Dr Chen and colleagues analysed data from 1742 people over the age of 45, who had been diagnosed with ulcerative colitis or Crohn’s disease and who were registered as part of Taiwan’s compulsory health insurance program.
They compared these patients’ cognitive health with that of more than 17,000 matched controls over the following 16 years.
“We found that among patients with IBD, there is more than doubling in the risk of developing dementia,” said study co-author Assistant Professor Hohui Wang, psychiatrist at University of California, San Francisco.
A total of 5.5% of patients with IBD developed dementia in the study period, compared with 1.4% of their peers.
In addition, these patients developed dementia seven years earlier than their peers, at age 76 on average, compared with 83.
“We were very surprised by such a strong association, and the significance of earlier onset of dementia among IBD patients,” Dr Chen said.
The type of dementia that increased the most was Alzheimer’s disease, and people who had IBD the longest were the most at risk of developing dementia overall.
Nevertheless, the team found no difference across sexes or whether the patient had ulcerative colitis or Crohn’s disease.
The research suggested the gut-brain axis and chronic inflammation played a role in neurocognitive degeneration, Dr Chen said.
A leaky gut and a poorer ability for the intestines to stop substances from the gut passing into the bloodstream could lead to a disrupted microbiome and more inflammation in the body.
Alzheimer’s disease, the most common type of dementia, is accompanied by neuroinflammation, a loss of neurons and problems with neurotransmitters.
Gut microbes can release neurotransmitters and neuromodulators, which then affect the brain, and the leaky gut that accompanies IBD may allow neurotoxic molecules made in the gut to travel to the brain.
“It is well established that the neurons and the immune system are in constant bidirectional communication and there are multiple pathways that dysbiosis might affect brain function in this scenario,” neuroscientist Elisa Hill, an associate professor at RMIT University, said.
This is troubling, because as the population ages, the burden of IBD and dementia grows.
“Vigilance and education for dementia among elderly patients with IBD may improve early intervention to slow cognitive decline and improve quality of life,” Dr Chen said.
Professor Hill said that although the observational study could not identify cause and effect, the results were “compelling”.
“The findings rely on a large database that contains information from all Taiwanese residents over 45 since 1995,” she said. “Using this approach, the study removes many biases such as patient selection, sex and socioeconomic factors.”
“To further unravel potential biological connections between dementia and IBD, it would be informative to compile a faecal microbial database from patients, together with detailed clinical records including medications and lifestyle information on diet and exercise,” she said.