Sir, we were delighted by the paper by Cerajewska et al.,1 which matches exactly our point of view presented briefly previously in this Journal2 describing the potential role of periopathogens in the development of cognitive impairment among elderly people.

The most recent, and perhaps the most methodologically sophisticated study3 published in PLOS One elucidated how IgG immunoglobulins response levels to common periodontal microbiota are associated with risk for developing incident of Alzheimer disease (AD) and play a role as a predictor of AD. This longitudinal research implemented the Washington Heights-Inwood Columbia Aging Project, a case-cohort study including 110 individuals with an incident of AD, northern Manhattan residents aged >65 years.

For the first time the analysis included a vast majority of causative periopathogens (seven genospecies) responsible for common inflammatory conditions of periodontal tissues. However, the serum level of antibodies to periopathogens alone may not reflect sufficiently the multidirectional interactions between infected periodontium and host response, potentially leading to AD. Therefore, further validation is required.

However, the newest publication4 (January 2015) gives the results of a retrospective analysis of a 37-year cohort study in Sweden, and does not indicate that decreased numbers of teeth were associated with dementia. Although, it is well-known that tooth loss is likely to be caused by advanced periodontitis, there are numerous other potential causes of reduced dentition. Hence, an association between periodontitis and Alzheimer disease cannot be reasonably concluded from such studies as stated in the article provided by Cerajewska.1 Undoubtedly, a local chronic inflammation may trigger a systemic inflammatory host response within different parts of the human body (brain, heart, vessels, joints).

Interestingly, the project of Birmingham Community Healthcare NHS Trust 'Outcomes of periodontal therapy in rheumatoid arthritis'5 explores the hypothesis that periodontal therapy aimed at eliminating gum infection can reduce joint and systemic inflammation in patients with rheumatoid arthritis.

The development of a novel vaccine for periodontopathogens, but not against single species alone, would be a great achievement contributing significantly to preventative strategies of systemic illnesses and public health.