For the study, Dr. Naoki Saji and colleagues at the National Center for Geriatrics and Gerontology in Obu, Aichi, Japan, analyzed stool samples from 128 older adults — with and without dementia.
In general, the investigators found, dementia patients had higher concentrations of certain compounds — including ammonia, indole and phenol — but lower levels of Bacteroides.
Bacteroides are a group of bacteria that can be beneficial in the gut because they crowd out “bad,” infection-causing bugs.
For now, Fargo said, the relationship between the gut microbiome and disease is an interesting, “burgeoning” area of research. But whether the microbes have any direct effect on dementia risk is unknown.
Other recent studies have looked at whether chronic infection has any connection to dementia. Just last week, researchers reported finding the bacteria that causes gum disease in the brains of people with Alzheimer’s.
In tests of mice, they showed that the bacteria could travel from the mouth to the brain, where they attacked nerve cells.
Still other research has found particularly high levels of certain strains of herpes virus in the brains of people with Alzheimer’s.
It all raises the possibility that “external organisms” might play some role in dementia, according to Fargo. But, he stressed, no one yet knows what’s going on.
Sano agreed. She said that although the presence of certain infectious bugs has been linked to dementia, it might not be the infections, themselves, that matter. Gum disease bacteria and herpes viruses are extremely common, Sano pointed out. So carrying those bugs, alone, is not the critical factor.
Instead, Sano speculated, there may be something about the body’s general response to “insult or injury” that is the real problem.
Fargo recommended that people focus on lifestyle factors that have been solidly tied to better brain health: Get regular exercise, don’t smoke and eat a heart-healthy diet.
He also pointed to the importance of keeping blood pressure down. A major trial published this week found that “intensive” blood pressure control — below 120 mm Hg — lowered older adults’ risk of developing milder problems with memory and thinking.