The research shows that as Alzheimer’s disease advances, indicators of poor oral health — including interdental plaque and gum bleeding — increase, while changes in the immune system also occur.

The study was conducted by scientists from the Hirszfeld Institute of Immunology and Experimental Therapy of the Polish Academy of Sciences in Wrocław, Wrocław Medical University and the University of Connecticut. The findings were published in 2025 in the International Journal of Molecular Sciences.

Researchers examined 68 participants: 36 patients diagnosed with Alzheimer’s disease, including its advanced stage, and 32 cognitively healthy individuals of similar age.

The team conducted detailed assessments of oral hygiene, measuring plaque accumulation in interproximal spaces, bleeding on probing, periodontal pocket depth and clinical attachment loss. Cognitive function was evaluated using the MMSE, MoCA and clock test.

Blood composition and immune markers were also analysed, including the cellular response to lipopolysaccharide derived from Porphyromonas gingivalis, a bacterium that is the main cause of periodontitis.

The analysis revealed changes in the immune cell profile of patients with Alzheimer’s disease. Researchers observed that overall white blood cell counts, as well as specific leukocyte subpopulations such as lymphocytes and monocytes, and platelet levels, were significantly lower than in cognitively healthy individuals.

They also identified a reduced systemic immune-inflammation index, which may indicate a weakened immune response to bacterial antigens.

“In patients with Alzheimer's disease, we see not so much excessive systemic inflammation, but certain deficits resulting from a weakened and exhausted immune system,” Jacek Zborowski from the Department of Periodontology and Oral Pathology at Wrocław Medical University said.

Researchers also found that unstimulated peripheral immune cells in Alzheimer’s patients produced significantly fewer pro- and anti-inflammatory cytokines than those in healthy individuals. However, after exposure to a bacterial antigen, their immune response became stronger than in the control group.

“It should be emphasised, however, that this is a more complex process, in which elements of chronic inflammation and functional changes in peripheral immune cells coexist and may play different roles in the pathogenesis of Alzheimer's disease,” project leader Marta Sochocka from the Hirszfeld Institute of Immunology and Experimental Therapy said.

One of the most notable findings of the study was the relationship between periodontal condition and cognitive performance. As Alzheimer’s disease progressed, both interdental plaque levels and bleeding on probing increased.

The researchers also found that greater gingival inflammation was associated with worse MMSE scores, regardless of age or gender.

“This is not about advanced periodontal disease. Our data suggest that even mild, chronic gingivitis can have systemic significance,” Zborowski added.

According to the researchers, poor oral hygiene and periodontal inflammation can place a constant burden on the ageing immune system. This may contribute to immune cell dysfunction and exaggerated responses to bacterial antigens.

With age, the blood-brain barrier becomes more permeable, allowing peripheral immune cells to participate in immune processes in the central nervous system, while additional inflammatory signals may influence inflammation in the brain. (PAP)

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