Taxonomic and functional signatures of smoking and periodontitis severity in the subgingival microbiome of older adults

Abstract Periodontitis and smoking are major contributors to oral and systemic health deterioration in aging adults. This study investigated the combined effects of smoking status and periodontitis severity on the subgingival microbiome in 1107 individuals aged 69–72 using shotgun metagenomic sequencing. Smoking was linked to reduced microbial diversity, enrichment of periodontal pathogens, and depletion of health-associated commensals, while increasing periodontitis severity was associated with broader dysbiotic shifts, including enrichment of canonical pathogens. The presence of overlapping taxa suggests shared dysbiotic pathways that may accelerate disease progression in older adults. Notably, the combination of smoking and severe periodontitis was characterized by enrichment of key pathogens, such as Tannerella forsythia , Fusobacterium nucleatum , Actinomyces israelii , and Mogibacterium timidum . Although former smokers showed fewer opportunistic pathogens than current smokers, their microbiomes remained altered compared to never smokers, suggesting persistent differences potentially related to past smoking. Functional profiling revealed largely additive effects of smoking and periodontitis, with enrichment of lipopolysaccharide biosynthesis, proteolysis, and sulfur metabolism, alongside depletion of commensal biosynthetic functions. Overall, the findings highlight the persistent and additive impacts of smoking and periodontitis on the subgingival microbiome, underscoring the importance of addressing both exposures jointly in long-term oral health strategies for older adults.