Two new studies are offering strong evidence that inflammatory bowel disease (IBD) and obesity are serious risk factors for developing dementia in later life. The studies are observational, and cannot determine causality, but they both build on prior research reaching similar conclusions.
The first study, from researchers at University College London, found obesity in subjects around the age of 50 correlated with a 31-percent increase in subsequent dementia compared to those within the normal body mass index (BMI) range.
The researchers evaluated data from the English Longitudinal Study of Ageing, investigating nearly 7,000 subjects who were followed for up to 15 years. Those subjects with a BMI over 30 at the beginning of the study were much more likely to develop dementia during the follow-up period compared to those with a BMI between 18.5 and 24.9 (classified as the normal range).
The relationship between obesity and dementia was higher in women, particularly in relation to abdominal obesity, which increased risk of dementia by 39 percent. However, this sex-specific difference in dementia development is not surprising considering women are generally much more likely to develop Alzheimer’s or dementia compared to men.
It is still unclear exactly what kind of causal mechanism may be linking mid-life obesity with later-life dementia. Considering how inconsistent the past epidemiological data linking obesity and dementia has been, the researchers on this new study suggest the association may be underpinned by a variety of comorbidities, inflammatory processes, and genetics.
“It is possible that the association between obesity and dementia might be potentially mediated by other conditions, such as hypertension or anticholinergic treatments,” says first author on the study, Yuxian Ma. “While not explored in this study, the research question of whether there an interactive effect between obesity and other midlife risk factors, such as hypertension, diabetes, and APOE ε4 carrier status, in relation to dementia will be investigated in upcoming work.”
The second study, led by a team of Taiwan-based researchers, investigated the relationship between dementia and IBD – primarily ulcerative colitis and Crohn’s disease. Growing understanding of the gut-brain connection has delivered compelling insights into the links between gut bacteria, inflammation, and mental health issues. And although neural inflammation is being investigated as a potential causal player in the onset of dementia, little research has specifically focused on whether bowel inflammation can be associated with later-life cognitive decline.
The new research looked at data following 1,742 patients for 16 years, with either ulcerative colitis or Crohn’s disease. Compared to a large, healthy, demographically matched control group, those subjects with either type of IBD were more than twice as likely to develop some form of dementia.
Most strikingly, Alzheimer’s disease appeared to be significantly linked, with IBD sufferers six times more likely to develop the disease than those in the control. This correlation was regardless of sex or type of IBD.
As with the obesity research, the study does not establish or explicitly propose a causal mechanism to explain this link between dementia and IBD. There are a number of hypothetical mechanisms suggested, such as a gut-brain pathway by which gut microbiome metabolites contribute to neurocognitive changes. However, the research also suggests lifestyle factors, or even particular IBD medications, could play a role in this association.
Although these observational studies do not offer scientists direct insights into what causes dementia, they do help direct future research and aid doctors in identifying those subjects most at risk at an early age.
The obesity study was published in the International Journal of Epidemiology, while the IBD study was published in the journal Gut.