September 18, 2026, 11:44 am | Read time: 6 minutes
The link between periodontal health, particularly gum inflammation, and dementia is not new. A recent long-term study has now examined more closely which characteristics of periodontitis are particularly closely associated with the later risk of dementia and Alzheimer’s. The results provide new insights into the connections between various aspects of periodontitis and different forms of dementia.
Previous studies have already linked periodontitis and certain oral bacteria such as Porphyromonas gingivalis with an increased risk of dementia and Alzheimer’s.1,2 Accordingly, regular tooth brushing might not only be important for healthy teeth but could also play a role in cognitive health. A connection between tooth loss and an increased risk of dementia has also been described.3 However, how exactly these connections come about is not yet fully understood. It remains unclear whether changes in oral flora are a cause or a consequence of cognitive impairments. Factors such as diet could also play a role.
A recent long-term study has examined the connection more closely.4 The focus was on identifying which signs of periodontitis could be associated with the later onset of dementia and Alzheimer’s.
Study Details
The study is based on data from the Hisayama Study, a population-based long-term study ongoing since 1961 in the town of the same name in southern Japan.5 For the current analysis, individuals aged 60 and older were considered. The baseline examination took place in 2007 and 2008.
Of the initial 2,002 participants, the authors excluded individuals who already had dementia. The absence of information on oral health or other relevant data was also a criterion for exclusion. Participants who no longer had their own teeth could not be included. Ultimately, 1,396 individuals were included in the analysis, specifically 622 men and 774 women.
The observation period ran until November 30, 2017, spanning more than ten years. The average follow-up period was 3,753 days, or about 10.3 years.
Assessment of Oral Health and Presence of Dementia
To assess the condition of the periodontal apparatus, researchers used various measurements. These included the average pocket depth at the gums and clinical attachment loss—this value (CAL) indicates how much the anchoring of the tooth in the periodontal apparatus has receded. The proportion of examined sites on the gums that bled during the examination was also considered. Additionally, researchers determined whether periodontitis was present according to the globally standardized classifications established in 2018.6
Unlike many earlier studies that relied solely on anonymous health insurance data, participants in this Japanese long-term study were clinically examined on-site by dentists.
Dementia diagnoses were also made based on established diagnostic criteria and verified by specialists through high-precision brain scans (such as MRI or CT) or tissue examinations. Medical information and, if available, brain imaging were also included in the study. The statistical analysis considered factors such as age, gender, education level, blood pressure, diabetes, body weight, smoking, alcohol consumption, physical activity, and the number of remaining teeth.
Certain Gum Changes More Strongly Associated with Dementia
During the observation period, 267 of the 1,396 participants developed dementia. This included 194 cases of Alzheimer’s dementia and 51 cases of vascular dementia. The latter form arises from circulatory disorders in the brain, where vascular damage prevents proper blood supply to the tissue. In 15 individuals, both forms occurred—these cases were counted in both groups for the respective analyses.
When considering all dementia cases, it was found that various measurements describing the condition of the gums and periodontal apparatus were associated with a higher risk of dementia. Participants with the greatest average gum pocket depth had about a 1.7 times higher risk of dementia than those with the lowest values. A greater loss of tooth anchoring in the periodontal apparatus and a higher proportion of bleeding sites were also associated with an increased risk.
Connection Between Alzheimer’s Dementia and Gum Bleeding
In Alzheimer’s dementia, a particular connection with gum bleeding was observed. Participants with the highest proportion of bleeding sites had about a 1.6 times higher risk than those with the lowest proportion. For vascular dementia, the significance was limited due to the significantly lower number of cases: Only 51 of the 1,396 participants developed this form of dementia. While the results partially indicated a connection with greater gum pocket depth, this was not statistically clear in one of the analyses. In another analysis, where pocket depth was considered as a continuous measurement, a statistically significant connection was found.
Even when repeated measurements of gum condition were considered, the fundamental finding remained: A poorer condition of the periodontal apparatus was associated with a higher overall risk of dementia.
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Significance of the Results
The results suggest that the condition of the periodontal apparatus in older adults could be linked to the later onset of dementia. Notably, the researchers did not only consider a single definition of periodontitis but various objectively measurable aspects of gum and periodontal health.
Markers for active, progressive inflammation—such as currently bleeding gums or deepened gum pockets—were particularly associated with specific dementia subtypes. In contrast, the mere tissue loss from the past (the so-called attachment loss) did not show this specific connection in the baseline analyses.
As a possible explanation for the observed connection, the authors cite inflammatory processes. In periodontitis, the immune system responds to inflammation in the tissue around the teeth. This leads, among other things, to the release of signaling substances that promote inflammatory reactions. It is conceivable that such processes could also affect the brain through the bloodstream. Prolonged inflammatory activity could, among other things, impair the blood-brain barrier and promote inflammation in the brain.
In vascular dementia, an influence on the blood vessels is conceivable. Inflammation and bacterial loads associated with periodontitis could impair vascular function. This could also affect the blood flow and vascular health of the brain.
Important: The results do not directly imply that periodontitis causes dementia or Alzheimer’s. The study shows a statistical connection—it provides clues to possible biological mechanisms. The actual role of oral health in the development of various forms of dementia needs further investigation.
Limitations
The greatest strength of the study lies in the long observation period. However, there are also limitations to note.
For instance, the number of participants with vascular dementia was relatively small, which limits the significance for this form of dementia. Additionally, various unrecorded factors could have influenced the results. Information on the nutritional status and any depression of the participants was missing. Depression can itself be associated with an increased risk of dementia and possibly also with oral health.
Furthermore, the examination of the periodontal apparatus was not complete. Certain areas on the tongue and palate sides were not recorded. This could have led to an underestimation of the actual extent of periodontitis. Additionally, all participants came from the same Japanese community. Whether the results can be generalized to other populations and countries remains uncertain.