- Although dementia is associated with an increased risk of poor oral health, the evidence supporting the role of oral health in dementia development is mixed.
- A recent meta-analysis synthesizing data from previous studies suggests that gum disease and tooth loss are associated with an increased risk of cognitive decline and dementia.
- These results underline the importance of maintaining oral health to reduce the risk of cognitive decline and dementia.
Individuals with dementia are often unable to maintain good oral hygiene and are at an increased risk of poor oral health. However, recent studies suggest that this relationship could be bidirectional.
A recent meta-analysis published in the
The evidence in the meta-analysis showed significant methodological variation and was of low quality. Still, the possible effects of cognitive decline on gum disease cannot be ruled out.
dr. Ella Cohn-Schwartz, a professor at Ben-Gurion University, Israel, who was not involved in this research, commented on it for Medical news today:
“Poor oral health and non-optimal chewing have been shown to be potentially modifiable risk factors for cognitive impairment, but prior evidence is limited. This meta-analysis provides a much-needed comprehensive synthesis of a large body of longitudinal studies related to periodontal health, cognitive decline and dementia.”
“This paper is new in several respects, such as considering reverse causality, covering the spectrum of periodontal decline, including tooth loss, and examining both cognitive decline and dementia as outcomes. Their findings may indicate the importance of policy and interventions that address tooth loss, even partial loss, in old age,” added Dr. Cohn-Schwartz to it.
Dementia is characterized by a gradual decline in cognitive function, including memory, thinking and reasoning, which impairs the individual’s ability to perform daily activities. Dementia is often preceded by milder forms of cognitive decline, such as:
Mild cognitive impairment refers to a decline in cognitive function greater than that typically seen with aging. Individuals with milder forms of cognitive decline do not show deficits in daily functioning, but are at increased risk of dementia.
Previous studies have shown that factors such as cardiovascular disease, diabetes and unhealthy diet can increase the risk of dementia. However, the role of oral health in the development of dementia has received less attention.
Until recently, some experts believed that poor oral hygiene due to impairment in daily functioning was responsible for the poor oral health seen in individuals with dementia. However, emerging evidence suggests that poor oral health, including gum disease, may contribute to cognitive decline and dementia.
A recent meta-analysis synthesized data from previous longitudinal studies examining the potential role of oral health in cognitive decline and dementia. Specifically, the meta-analysis examined the impact of periodontal disease, also known as gum disease, on cognitive health.
Periodontitis refers to the bacterial infection of the gums that causes inflammation. The inflammation of the gums can damage the tissue and bones that support the teeth and can lead to tooth loss in severe cases.
The most common signs of periodontitis are bleeding gums, loss of alveolar bones that support the teeth, and tooth loss. Periodontitis is also characterized by an increase in the depth of periodontal pockets, the spaces between the gums and teeth.
The meta-analysis included 24 longitudinal studies examining the association between cognitive decline and periodontitis, and an additional 23 studies examining the association between periodontitis and dementia.
It evaluated periodontal health assessed based on the presence of periodontitis, alveolar bone loss, increased periodontal pocket depth, and tooth loss.
The meta-analysis found that periodontitis was associated with an increased risk of cognitive decline and dementia. Among the various criteria used to assess periodontitis, further analysis found that tooth loss was also independently associated with cognitive decline and dementia.
Partial tooth loss, in which some but not all teeth were lost, was associated with cognitive decline. In contrast, complete tooth loss, but not partial tooth loss, was linked to an increased risk of dementia.
Previous studies have shown that individuals with dementia or mild cognitive impairment can lead to poor oral health.
The decline in cognitive function and brain changes associated with mild cognitive impairment or dementia occurs gradually over many years. Thus, studies with a follow-up of less than 10 years could potentially reflect the impact of cognitive decline on oral health.
Therefore, the researchers re-examined the association between cognitive health and periodontal health after excluding studies with a follow-up duration of less than 10 years. After excluding these studies, the meta-analysis found a weaker association between periodontitis and dementia.
The weaker association between periodontitis and dementia in this additional analysis indicates that the results of the first analysis may have been influenced in part by the effects of cognitive impairment on oral health.
While the results in the follow-up analysis indicated that poor oral health may contribute to the development of dementia, some researchers remain skeptical about the evidence linking poor oral health to cognitive decline.
This is because dementia and tooth loss share the same risk factors, such as low education, socioeconomic status and diabetes.
In addition, individuals with higher cognitive function in childhood generally have better oral health and access to dental care in adulthood than individuals with lower cognitive capacity in early life.
Children with higher cognitive abilities are also more likely to maintain better cognitive function in old age. It is therefore possible that poor oral health does not play a causal role in the development of dementia.
dr. Murray Thomson, a professor of dentistry at the University of Otago not involved in the current research, noted:
“The findings of this review are not surprising, as gum disease and cognitive decline share the same risk factors throughout life. I would therefore expect any study at any age to show a link between gum disease and cognitive function. Most importantly, there is no good evidence that gum disease causes poor cognitive function, but there is very good evidence that people with poor cognitive function have more gum disease.”
The authors cautioned that the evidence reviewed in the meta-analysis was of low quality. There was significant variation between the analyzed studies in the measurements used to assess periodontal health and the tests used to evaluate cognitive function.
In addition, the studies assessing the impact of cognitive decline on periodontal health generally included individuals over 65 years of age and with shorter follow-up duration. This may have biased the results in favor of a positive association between periodontal health and cognitive decline.
Thus, there is a need for more research using standardized methods to further assess the association between periodontal and cognitive health.
Still, these results suggest that the prevention and early treatment of oral health problems may help reduce the risk of cognitive decline and dementia.
The mechanisms that might explain the impact of periodontal health on cognitive impairment are not well understood. The bacterial infection responsible for gum disease is known to cause an increase in markers of systemic inflammation.
Several studies suggest that systemic inflammation may contribute to the development of dementia. Systemic inflammation caused by periodontitis can thus potentially lead to a decline in cognitive function.
The bacterial infection and inflammation involved in periodontitis can also weaken the blood-brain barrier, preventing toxins from entering the brain.
Weakening of the blood-brain barrier could allow the bacteria and inflammatory molecules to enter the brain through the bloodstream and then contribute to brain inflammation. Periodontitis can thus cause brain inflammation, which plays a crucial role in the development of dementia.
Deficiencies in chewing ability due to tooth loss can also contribute to the decline in cognitive function. This is because the process of chewing food is associated with increased blood flow to areas of the brain involved in cognition and helps maintain cognitive function.
In addition, the reduced ability to chew food due to tooth loss can affect dietary habits, including higher sugar consumption and lower dietary fiber intake. Unhealthy dietary habits linked to the loss of chewing ability due to tooth loss may also increase the risk of dementia.