Study links tooth loss to dementia risk in older adults

A recent study published in the journal of the American Medical Directors Association suggests that poor oral health, particularly tooth loss, may be linked to an elevated risk of developing dementia. While previous research has established connections between oral hygiene and cognitive decline, this specific factor was not included among the 14 modifiable risk factors identified in the updated Lancet Commission results from 2024. Those findings also informed World Health Organization guidelines issued this year aimed at reducing dementia risk.

How researchers analyzed aging data

The investigation relied on data from 47,293 participants aged 65 years or older who were part of the Japanese Gerontological Evaluation Study. Researchers tracked these individuals for approximately nine years, spanning from 2013 to 2022. During this observation period, 8,247 participants developed dementia, representing 17.4% of the sample.

The team sought to determine how poor oral health, measured by the number of remaining teeth, correlated with dementia incidence compared to known risk factors outlined by the Lancet Commission. Two factors could not be assessed within the study's dataset: high LDL cholesterol levels and air pollution. The research group, which included student Ma Ho Iwata from Tohoku University, utilized the count of remaining teeth as a proxy for oral health status. They reasoned that tooth loss typically reflects a long history of oral diseases, such as advanced dental caries and severe gum disease.

Dementia rates rise with fewer teeth

Statistical analysis revealed a clear association between declining tooth counts and increased annual dementia incidence rates:

• 1.63 cases per 100 people with 20 or more teeth.
• 2.31 cases per 100 people with 10 to 19 teeth.
• 2.97 cases per 100 people with 1 to 9 teeth.
• 4.34 cases per 100 people who had lost all their teeth.

After adjusting for sex, age, and income, the relative risk of dementia increased as the number of teeth decreased compared to those with 20 or more teeth:

• 14% higher risk for individuals with 10 to 19 teeth.
• 12% higher risk for individuals with 1 to 9 teeth.
• 27% higher risk for individuals with no teeth.

Gender differences in risk attribution

Researchers employed a statistical method known as "population attributable fraction" to estimate each risk factor's contribution to the disease at a societal level, assuming a causal role. By this metric, tooth loss accounted for 7.2% of dementia cases in the study. This figure ranked third among all risk factors, trailing behind depressive symptoms at 10.5% and social isolation at 9.4%.

A notable finding emerged regarding gender disparities. Among men only, tooth loss recorded the highest percentage among all risk factors in the study at 12%. In contrast, it ranked fourth among women at 6.1%. The researchers suggest this outcome may indicate that tooth loss contributes to dementia cases more significantly than well-known factors such as physical inactivity, smoking, and low educational attainment.

Does tooth loss cause dementia?

The study does not establish a direct causal link. The authors clarify that the results do not prove causation, noting that the data relies on self-reported information from participants, which introduces potential errors or bias. However, the team proposes several pathways that might explain the observed correlation:

• Impaired chewing ability and food intake, potentially leading to malnutrition.
• Social isolation, which is itself a recognized risk factor for dementia.
• Oral inflammation, which may trigger systemic inflammation contributing to cognitive decline.

The researchers state that their findings hold significant public health importance and advocate for integrating oral health into strategies for dementia prevention.