Change of oral microbiome diversity by smoking across different age groups.

Introduction: The oral microbiome, a complex ecosystem linked to both oral and systemic diseases, undergoes compositional and functional changes with aging. Tobacco exposure is a known disruptor of microbial homeostasis, yet its effect on microbial diversity remains inconsistent. Whether agingmodifies the relationship between smoking and the oral microbiome remains unclear. This study aimed to evaluate (1) the association between serum cotinine and oral microbial diversity, (2) whether this association varies by age, and (3) taxonomic shifts that may explain smoking-related dysbiosis. Method: We analyzed data from 4,387 adults aged 30-69 years in the U.S. National Health and Nutrition Examination Survey 2009-2012. Serumcotinine, an objective biomarker of nicotine exposure, was used as the primary exposure. Oral microbiome diversity was assessed via Results: Serum cotinine was inversely associated with alpha diversity, particularly in current smokers aged 60-69 years (adjusted β = -0.1081, Discussion: This highlights the synergistic impact of aging and smoking on the oral microbiome and underscores the need for age-specific prevention strategies. Prospective studies are warranted to confirm causality and assess the reversibility of smoking-induced dysbiosis.