A nice smile is visually attractive, but it can also be a sign of cognitive health. Numerous studies have found a connection between poor oral hygiene and dementia.
Tooth loss has been shown to be a risk factor for cognitive impairment and dementia. A meta-analysis of 14 studies including over 34,000 participants found that tooth loss was associated with an approximately 1.5 times higher risk for cognitive impairment [1]. The effect was dose-dependent, such that the risk increased 1.4% with each additional tooth lost. Some studies have shown that denture wearers also have increased dementia risk [2; 3]. Since dentures serve as a replacement for missing teeth, denture wearing can also be considered a surrogate for tooth loss. However, those with dentures appeared to be at lower risk relative to individuals with uncorrected tooth loss [1; 4].
The association between tooth loss and cognitive decline is related to multiple factors, which include chronic inflammation, socioeconomic status, and nutritional status [5]. The effect of dentures may be related to the latter two, as it may be an indication of better access to dental care, and because uncorrected tooth loss impacts the ability to chew food, it may lead to nutritional deficiencies [1].
Studies have found that dementia patients are at higher risk for developing gum disease and that those with gum disease are at higher risk for dementia [6; 7]. Poor oral hygiene and inadequate nutrition are likely the primary drivers for the risk of gum disease in dementia patients, particularly as the disease progresses. Inflammation is thought to be the primary mechanism by which gum disease increases the risk for cognitive decline.
The mouth is home to hundreds of species of bacteria, and while most are harmless, a few types, such as Porphyromonas gingivalis, can promote gum disease. Patients with Alzheimer’s disease were found to be more likely to have higher proportions of the harmful gum disease-related bacteria species [8]. Poor oral hygiene can lead to the buildup of bacteria on the teeth, leading to inflammation of the gums, called gingivitis [9]. If not treated, the bacteria can continue to accumulate and work their way under the gums, leading to a chronic infection called periodontitis. The presence of the bacteria in the gums triggers an immune response, and its persistence can lead to chronic inflammation.
Studies in animals have shown that both the bacteria and the inflammatory mediators can make their way from the mouth to the blood to the brain [10]. Bacteria associated with gum disease, such as P. gingivalis, have been found in the brains of Alzheimer’s disease patients [11]. Once in the brain, the bacteria can trigger an immune response and promote inflammation. It may also trigger brain pathology associated with Alzheimer’s disease, such as amyloid.
The ability of gum disease to trigger systemic inflammation likely also underlies its association with diabetes and cardiovascular disease, which are themselves risk factors for dementia [12]. Inflammation may be a common mechanism linking all of these risk factors together. Similarly, a poor diet increases the risk for all of these conditions. A diet rich in processed foods that contain lots of easily digestible sugars can promote the growth of the disease-causing bacteria in the mouth. Eating too much sugar can also lead to metabolic changes that promote inflammation, and make the immune system more vulnerable to infections.
Good oral hygiene is multi-faceted [13]. It involves routine dental care, diet, and management of chronic diseases. Some medications cause dry mouth, which can promote bacterial growth. Diets rich in high-fiber fruits and vegetables can promote the growth of healthy bacteria. Help protect your brain by taking care of your teeth with daily brushing and flossing. If these activities result in gum pain or bleeding, it may be a sign of gingivitis, so be sure to have it checked out while it is still at this early, treatable stage, before it progresses to periodontitis.
Betsy Mills, PhD, is a member of the ADDF's Aging and Alzheimer's Prevention program. She critically evaluates the scientific evidence regarding prospective therapies to promote brain health and/or prevent Alzheimer's disease, and contributes to CognitiveVitality.org. Dr. Mills came to the ADDF from the University of Michigan, where she served as the grant writing manager for a clinical laboratory specializing in neuroautoimmune diseases. She also completed a Postdoctoral fellowship at the University of Michigan, where she worked to uncover genes that could promote retina regeneration. She earned her doctorate in neuroscience at Johns Hopkins University School of Medicine, where she studied the role of glial cells in the optic nerve, and their contribution to neurodegeneration in glaucoma. She obtained her bachelor's degree in biology from the College of the Holy Cross. Dr. Mills has a strong passion for community outreach, and has served as program presenter with the Michigan Great Lakes Chapter of the Alzheimer's Association to promote dementia awareness.
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