Longitudinal monitoring of patients suggests a causal link between chronic 
periodontitis and the development of Alzheimer's disease (AD). However, the 
explanation of how periodontitis can lead to dementia remains unclear. A working 
hypothesis links extrinsic inflammation as a secondary cause of AD. This 
hypothesis suggests a compromised oral hygiene leads to a dysbiotic oral 
microbiome whereby Porphyromonas gingivalis, a keystone periodontal pathogen, 
with its companion species, orchestrates immune subversion in the host. Brushing 
and chewing on teeth supported by already injured soft tissues leads to 
bacteremias. As a result, a persistent systemic inflammatory response develops 
to periodontal pathogens. The pathogens, and the host's inflammatory response, 
subsequently lead to the initiation and progression of multiple metabolic and 
inflammatory co-morbidities, including AD. Insufficient levels of essential 
micronutrients can lead to microbial dysbiosis through the growth of periodontal 
pathogens such as demonstrated for P. gingivalis under low hemin 
bioavailability. An individual's diet also defines the consortium of microbial 
communities that take up residency in the oral and gastrointestinal (GI) tract 
microbiomes. Their imbalance can lead to behavioral changes. For example, 
probiotics enriched in Lactobacillus genus of bacteria, when ingested, exert 
some anti-inflammatory influence through common host/bacterial neurochemicals, 
both locally, and through sensory signaling back to the brain. Early life 
dietary behaviors may cause an imbalance in the host/microbial endocrinology 
through a dietary intake incompatible with a healthy GI tract microbiome later 
in life. This imbalance in host/microbial endocrinology may have a lasting 
impact on mental health. This observation opens up an opportunity to explore the 
mechanisms, which may underlie the previously detected relationship between 
diet, oral/GI microbial communities, to anxiety, cognition and sleep patterns. 
This review suggests healthy diet based interventions that together with 
improved life style/behavioral changes may reduce and/or delay the incidence of 
AD.