Tooth Loss May Make Memory Decline In Ageing Mice — Researchers

 

Researchers at Hiroshima University said tooth loss doesn’t just make eating harder; it may also make thinking more challenging.

In a new study, the researchers in animal studies found that ageing mice missing their molars experience measurable cognitive decline, even when their nutrition remains perfectly intact.

Published in the Archives of Oral Biology, they reported that tooth loss could predict

memory problems regardless of protein intake.

Low protein intake has long been linked to frailty, muscle loss and cognitive impairment in older adults, leading researchers to question whether memory decline observed in people with poor oral health stems from nutritional deficiencies or from reduced chewing ability itself.

Rie Hatakeyama, a postdoctoral researcher at Hiroshima University’s (HU) Graduate School of Biomedical and Health Sciences and first author of the study, explained that tooth loss is common in ageing populations, yet its direct neurological impact has remained unclear.

“Our study examines whether tooth loss itself, independent of nutritional deficiency such as a low-protein diet, can cause cognitive decline in male mice,” said Hatakeyama.

To explore how chewing ability and nutrition jointly influence the brain, the research team used ageing-prone male mice and assigned them to one of four conditions: a normal-protein diet with no tooth extraction, a low-protein diet with no extraction, molar extraction with a normal-protein diet, and molar extraction with a low-protein diet.

After six months, the mice underwent behavioural tests and detailed analyses of their brain tissue for markers of inflammation, neuronal loss, and cell death–related gene expression.

Side-by-side video showing mice navigating the Barnes maze. The mouse on the left belongs to the control group (normal protein diet), while the mouse on the right belongs to the tooth loss group (normal protein diet).

At 3 months of age, mice underwent either tooth extraction or a sham operation and were assigned to either a normal-protein diet or a low-protein diet. Behavioural testing and brain analyses were conducted six months later.

The results were striking: mice that lost their molars showed significant memory decline even though they received the same diet as the control groups. By contrast, a low-protein diet alone had only limited effects on cognition.

Brain analyses supported these findings. Tooth loss was associated with increased neuroinflammation and neuronal loss in the hippocampus, particularly in the CA1 and dentate gyrus regions, which are critical for memory formation.

This study adds to growing evidence that links oral health to brain health and that protecting one’s chewing ability may be a simple but powerful strategy for preserving cognitive function with age.

The research team plans to further investigate the biological mechanisms connecting mastication to brain health, including changes in hippocampal activity, neurotransmitter levels, and neurogenesis.

“Our ultimate goal is to demonstrate, in humans, that maintaining or restoring mastication through prosthodontic treatment can help prevent or delay cognitive decline in the elderly,” Hatakeyama said.

Research teams around the world are suggesting that gum disease and tooth loss involve chronic inflammation, which could ripple out toward the brain. Another suggestion is that the sensory input of chewing sends signals through nerves and into regions of our brain involved in learning and memory. Remove teeth, and those signals disappear.

Last year, researchers from New York University urged The Lancet to formally recognise oral health as a modifiable dementia risk factor, arguing that poor oral health may carry nearly three times the dementia risk associated with diabetes or hypertension.