As interest in gut bacteria peaks, they are implicated in yet another condition. Researchers recently identified stark differences in levels of specific gut bacteria in people with dementia.

Our bodies swarm with microscopic visitors. On our skin, in our mouths, deep in our lungs, and, of course, nestled in our digestive systems. The bacteria in the gut have long been known to assist the digestive process, but in recent years, it has become clear that they are involved in much, much more. With bacteria now implicated in conditions as diverse as diabetes and schizophrenia, we truly are in the age of the microbiome. Recently, researchers in Japan investigated whether gut bacteria might, one day, help in the diagnosis and even treatment of dementia.

Dr. Naoki Saji, from the Center for Comprehensive Care and Research on Memory Disorders at the National Center for Geriatrics and Gerontology in Obu, Japan, led the team of scientists. The researchers will present their findings at the American Stroke Association's International Stroke Conference 2019 in Honolulu, HI.

Examining feces

The researchers recruited 128 participants from their memory clinic. The average age was 74.2, and 59% were female. Cognitive ability was assessed using neuropsychological tests, and each participant's brain was scanned using magnetic resonance imaging (MRI). Some participants had a dementia diagnosis; others did not. Next, the scientists analyzed stool samples to look for differences.

As the authors expected, there were measurable differences in the samples from people with dementia and from those without it. In particular, the feces of individuals with dementia had higher levels of ammonia, indole, skatole, and phenol. As an aside, both indole and skatole have an intense fecal odor in large concentrations but, surprisingly, at lower concentrations, they have a flowery smell; in fact, they occur naturally in a number of flower species.

Change in bacterial populations

In the feces of participants with dementia, the scientists also measured significant changes in the levels of certain gut bacteria. They found lower levels of the genus Bacteroides, which are considered "good" bacteria. Bacteroides break down toxic plant material into sugars that the human body can use. Individuals with dementia were also shown to have higher levels of the genus Ruminococcus than those without dementia.

"Although this is an observational study and we assessed a small number of patients, the odds ratio is certainly high, suggesting that gut bacteria may be a target for the prevention of dementia."

—Lead author Dr. Naoki Saji

This study is not the first to link changes in gut bacteria to dementia, but scientists are still debating exactly how gut bacteria influence the brain. Some authors believe that because gut bacteria can influence the immune system, and therefore levels of inflammation, this might provide part of the answer—chronic inflammation has already been linked to neurodegenerative conditions.

Hope for the future

Dementia is a huge concern. Currently, Alzheimer's—the most common form of dementia—affects an estimated 5.7 million people in the US. Worldwide, the figure is around 47 million, and it is predicted to rise to 75 million by 2030.

As the US population's average lifespan slowly extends, dementia is likely to increase in step. As yet, there is no cure, so researchers are focused on understanding the processes behind the disease. Although the current trial was small-scale, there were marked differences between stool samples. The authors conclude that "gut microbiota is an independent and strong risk factor for dementia."

Future work will need to tease apart cause and effect: Are the differences in gut bacteria a result of dementia, or do the changes in gut bacteria trigger dementia? This innovative new study provides fresh insight and, perhaps, a potential route to earlier diagnosis and future interventions.