Mouth to mind: Is your oral health putting you at Alzheimer's risk?

The human brain remains one of the greatest mysteries in science, controlling virtually every function in the body. Like a highly sophisticated computer, it processes information and coordinates bodily functions through the nervous system.

However, when the brain is compromised, the entire body can be affected. Studies show that pain, infections, and systemic diseases can trigger brain disorders, including mental health conditions and neurodegenerative diseases such as Alzheimer’s and dementia.

Recent research has highlighted a surprising connection between oral health and Alzheimer’s disease, suggesting that a bacterial infection in the mouth could contribute to the development of the condition. In addition to oral infections, other distress signals from different body organs have also been linked to cognitive decline.

For years, scientists have investigated the possible links between infections and Alzheimer’s disease. A 2019 study published in the journal Science Advances suggested that Porphyromonas gingivalis, the bacterium responsible for gum disease, may play a role in the development of Alzheimer’s. Further experiments on mice showed that an oral infection with the pathogen led to brain colonisation and an increase in amyloid-beta, the sticky protein commonly associated with Alzheimer’s disease.

The research team also identified toxic enzymes called gingipains, which the bacteria secrete. These enzymes were found in the brains of Alzheimer’s patients and were linked to markers of the disease, including tau protein and ubiquitin. More strikingly, traces of gingipains were detected in individuals who had not yet been diagnosed with Alzheimer’s, suggesting that the infection might be a precursor to cognitive decline.

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While the study did not definitively prove causation, it provided compelling evidence that chronic oral infections could contribute to Alzheimer’s. This supports the hypothesis that addressing gum disease may reduce the risk of developing neurodegenerative diseases.

While gum disease has emerged as a potential risk factor for Alzheimer’s, other conditions in the body can also affect brain function. Several studies suggest that issues in the cardiovascular system, gut health, and even musculoskeletal pain can contribute to cognitive decline and dementia.

Poor heart health is a well-documented risk factor for dementia. The World Health Organisation (WHO) and Alzheimer’s Disease International estimate that around 55 million people worldwide are living with dementia, with numbers expected to rise as populations age. A significant portion of these cases is linked to vascular dementia, which results from impaired blood flow to the brain. Hypertension (high blood pressure), high cholesterol, and atherosclerosis (plaque buildup in arteries) can damage blood vessels, reducing oxygen supply to the brain and leading to neuron death.

Research conducted by Professor Raj Kalaria of Neuropathology at Newcastle University’s Translation and Clinical Research Institute found that Africans are particularly susceptible to vascular dementia due to high rates of hypertension. “Addressing cardiovascular risk factors through lifestyle changes and medication can help prevent cognitive decline,” he said during the Future of Dementia in Africa conference held in Nairobi.

The gut and brain are intricately connected through what scientists call the gut-brain axis. The gut microbiome, consisting of trillions of bacteria, influences brain function through metabolic and inflammatory pathways. Imbalances in gut bacteria have been linked to conditions such as depression, anxiety, and even Alzheimer’s disease. An ongoing study conducted by Dr Chi Udeh-Momoh and Dr Zul Merali at the Brain and Mind Institute highlighted that inflammatory microbes in the gut could trigger neuroinflammation, leading to the death of brain cells.

Emerging evidence suggests that probiotics and dietary changes may support brain health by maintaining a balanced gut microbiome. Pain and inflammation in other parts of the body can also impact brain health, says Dr Chi Udeh-Momoh, neuroscientist at the Brain and Mind Institute. Research has shown that chronic pain conditions, such as arthritis, migraines, and fibromyalgia, are associated with an increased risk of dementia.

“Pain triggers the release of stress hormones, which, over time, can damage brain cells and impair cognitive function. For example, a simple toothache can cause significant distress to the brain. When the nervous system sends pain signals, the brain prioritises processing those signals, potentially leading to cognitive fog and memory issues,” she explains.

This highlights the importance of addressing chronic pain not just for physical relief, but also for long-term brain health.

Meanwhile, leading neuroscientists, healthcare professionals, and researchers gathered at the Aga Khan University’s Brain and Mind Institute to discuss a growing public health crisis—dementia and Alzheimer’s disease. The conference underscored Africa’s rising dementia burden and the urgent need for localised research.