Is there a link between oral bacteria and the development of Alzheimer's disease?
There is a consistent association between oral bacteria and Alzheimer's disease, but a proven cause-and-effect relationship in humans has not yet been established. Good oral care is sensible, but do not expect it to offer proven protection against Alzheimer's disease.
P. gingivalis, the key bacterium in gum disease, has been found in the brain tissue of people who died from Alzheimer's disease. A meta-analysis of 16 studies found that when oral bacteria were detectable in the brain, the likelihood of Alzheimer's disease was increased more than tenfold. For P. gingivalis specifically, that figure was approximately sixfold. The toxic enzymes produced by this bacterium (gingipains) correlated with typical Alzheimer-related abnormalities in brain tissue.
Alzheimer's patients also have lower diversity of oral bacteria than people with healthy memory function. This association has been found consistently across multiple clinical studies, but whether gum disease actually causes Alzheimer's disease has not yet been demonstrated in humans. For now, these remain associations, not a proven cause-and-effect relationship.
Animal and laboratory research does provide biologically plausible mechanisms. Repeated exposure to P. gingivalis led in mice to colonisation of the brain, increased production of beta-amyloid (the building block of Alzheimer's plaques), greater inflammation in the brain, and deterioration of cognitive functioning. In cell studies using human brain cells, components of the bacterial cell wall triggered inflammatory responses, amyloid production, and mitochondrial damage. How this travels exactly from the mouth to the brain has not yet been fully clarified; one hypothesis is that small vesicles secreted by the bacterium are able to cross the blood-brain barrier.
Gingipain inhibitors reduced bacterial infection in the brain and protected brain cells in mouse studies. However, in humans with mild to moderate Alzheimer's disease, such an inhibitor had no measurable effect on cognition. That result is a serious caveat regarding the expectation that this therapeutic pathway will work. Whether keeping your oral health in order can prevent Alzheimer's disease is equally unproven in clinical terms. Given the association and the absence of risk, good oral care is worth considering regardless, but it is not a proven form of protection.
Evidence based on a meta-analysis/systematic review (16 studies), multiple reviews, animal and cell studies, and one clinical intervention study with a gingipain inhibitor. Associations are consistent; causality in humans has not been demonstrated.
Is there a relationship between changing body odour and Alzheimer's disease?
There is a link between Alzheimer's disease and changing body odour, particularly through smell loss as an early signal. Use it as a reason to speak with your doctor, not as evidence of dementia.
Does a daily multivitamin help protect memory in older age?
A daily multivitamin appears to be able to protect memory in older people who are at risk of deficiencies or have a history of cardiovascular disease, but for well-nourished older adults the benefit has not been convincingly demonstrated.
Is there a link between depression and a higher risk of dementia?
Depression is strongly associated with a higher risk of dementia, though it remains uncertain whether depression causes dementia or is sometimes an early sign of it. Treating depression appears to lower the risk, so if you or someone close to you is experiencing depressive symptoms, it is worth taking them seriously and discussing them with a doctor.
What does research say about the relationship between lithium and memory?
Lithium slows cognitive decline in mild memory problems and early Alzheimer's disease, but for healthy people or as a preventive measure there is no evidence of memory improvement. If you use lithium for a psychiatric condition, discuss any memory complaints with your treating clinician, as these are often linked to your mood rather than the medication.
Is there a link between your hormones and the risk of dementia later in life?
Can you prevent dementia with your lifestyle?
Lifestyle does meaningfully influence your risk of dementia: one third of all cases are linked to modifiable factors such as physical activity, blood pressure and smoking. Especially if you already have an elevated risk, tackling several things at once is worthwhile.