Inflammatory bowel disease (IBD) -- including colitis and Crohn's disease -- correlates with a doubled risk of developing dementia, scientists reported Wednesday in the journal Gut.

Moreover, various forms of dementia were diagnosed some seven years earlier in people with IBD compared to those without the condition, the study showed.

While the cause of IBD is not clear, it is thought to develop from an impaired immune response to changes in the microbiome -- the community of microorganisms that live in the body.

Recent research has revealed previously unsuspected linkages between our gut, central nervous system, and the microbiome. 

This "gut-brain axis" is implicated in various aspects of health and disease.

Other research, meanwhile, has shown that IBD might play a role in the development of Parkinson's disease. 

But it remained unclear if IBD was also linked to a heightened risk of dementia.

To find out more, a team led by Chen Mu-Hong, a doctor at Taipei Veterans General Hospital, drew on data for 1,742 people aged 45 and over who had been diagnosed with either ulcerative colitis or Crohn’s disease between 1998 and 2011.

Cognitive health was tracked for 16 years following their IBD diagnosis and compared with that of 17,420 people who were matched for sex, age, access to healthcare, income, and underlying conditions but who didn't have IBD. 

During the monitoring period, 5.5 percent of individuals with IBD developed dementia, including Alzheimer's disease, compared to 1.5 percent for those without IBD.

Those with IBD were diagnosed with dementia an average of seven years earlier.

After taking account of potentially confounding factors, the researchers determined that people with IBD were more than twice as likely to develop dementia.

The risk for Alzheimer's disease was six times greater.

"The identification of increased dementia risk and earlier onset among patients with IBD suggest they might benefit from education and increased clinical vigilance," the study concluded.

The findings were the same for men and women.

Because this is an observational study, it cause and effect can only be inferred, not proven, the researchers noted.

Nor were the researchers able to gather information on potentially influential lifestyle factors, such as diet and exercise, or assess the impact of anti-inflammatory drugs.