BACKGROUND: Chronic inflammation in periodontal disease has been suggested as a 
potential risk factor in Alzheimer's disease (AD). The purpose of this study was 
to examine serum antibody levels to bacteria of periodontal disease in 
participants who eventually converted to AD compared with the antibody levels in 
control subjects.
METHODS: Serum samples from 158 participants in the Biologically Resilient 
Adults in Neurological Studies research program at the University of Kentucky 
were analyzed for immunoglobulin G antibody levels to seven oral bacteria 
associated with periodontitis, including Aggregatibacter actinomycetemcomitans, 
Porphyromonas gingivalis, Campylobacter rectus, Treponema denticola, 
Fusobacterium nucleatum, Tannerella forsythia, and Prevotella intermedia. All 
158 participants were cognitively intact at baseline venous blood draw. In all, 
81 of the participants developed either mild cognitive impairment (MCI) or AD or 
both, and 77 controls remained cognitively intact in the years of follow-up. 
Antibody levels were compared between controls and subjects with AD at baseline 
draw and after conversion and controls and subjects with MCI at baseline draw 
and after conversion using the Wilcoxon rank-sum test. AD and MCI participants 
were not directly compared. Linear regression models were used to adjust for 
potential confounding.
RESULTS: Antibody levels to F nucleatum and P intermedia were significantly 
increased (α = 0.05) at baseline serum draw in the patients with AD compared 
with controls. These results remained significant when controlling for baseline 
age, Mini-Mental State Examination score, and apolipoprotein epsilon 4 status.
CONCLUSIONS: This study provides initial data that demonstrate elevated 
antibodies to periodontal disease bacteria in subjects years before cognitive 
impairment and suggests that periodontal disease could potentially contribute to 
the risk of AD onset/progression. Additional cohort studies profiling oral 
clinical presentation with systemic response and AD and prospective studies to 
evaluate any cause-and-effect association are warranted.