Making Sense of Research

By Dennis McCormac, Ph.D.,  i-Forget Advisory Board Member

People who have Alzheimer’s disease are less likely to develop colorectal cancer and vice versa. A group of Chinese researchers set out to confirm the relationship between the two diseases and what might be at play. 

The researchers used mice for insights because they can be experimentally induced to develop dementia or colon cancer. It would be impossible to do this kind of research on human beings. 

The researchers injected a chemical that causes colorectal cancer into mice with pre-existing Alzheimer's disease and those without.

Compared to mice with normal brain function, those with Alzheimer’s disease developed fewer colorectal tumours when exposed to the colon cancer-causing chemical. The study pointed to the inverse relationship between the two diseases.

When the researchers sequenced the DNA of the gut organisms in gut tumour-free mice with Alzheimer’s disease and humans with Alzheimer’s symptoms, they found two bacterial species that were more abundant than in the gut of people with colorectal cancer. The two families of bacteria are Prevotella and Bacteroides. When these two types of bacteria were removed from the intestines of mice with cognitive impairment, the protective effect of cognitive impairment against developing a gut tumour disappeared. This result indicates that something about these bacteria is inhibiting tumour growth and may point the way to new colon cancer prevention strategies. 

This research supports the study’s hypothesis and goes on to implicate the bacteria involved. However, further work needs to be done to see if it holds true for humans. 

The confirmation of the inverse relationship between Alzheimer’s disease and colorectal cancer supports the i-Forget study’s hypothesis that an imbalanced gut microbiota facilitates both cognitive decline and can influence a broad variety of human conditions. The findings also show promise for preventing colorectal cancer. 

October 2024