Association between dental flossing frequency and oral microbiome in U.S. adults

The oral microbiome is vital for health, yet population-based evidence on how self-reported flossing relates to microbial communities remains limited. This study examined the association between self-reported dental flossing frequency and oral microbiome diversity in a nationally representative sample of U.S. adults. This cross-sectional analysis included 4,772 adults aged 30-69 from NHANES 2009–2012. Flossing frequency was categorized as non-users (0 days/week), some flossing (1-6 days/week), and daily users (7 days/week). Oral microbiome composition was profiled using 16S rRNA sequencing. α-diversity was calculated using Observed amplicon sequence variants (ASVs), Shannon, Inverse Simpson, and Faith’s Phylogenetic Diversity (PD); β-diversity using Bray–Curtis and UniFrac distances. Survey-weighted linear regression and PERMANOVA were used with covariate adjustment. Participants included, non-users (32%), some flossing (38%), and daily users (30%). A dose–response relationship was observed between flossing frequency and reduced microbial richness and phylogenetic diversity. Compared with non-users, daily users exhibited significantly lower richness (Observed ASVs: β = −11.46, 95% CI: −15.62 to −7.29) and phylogenetic diversity (Faith’s PD: β = −0.88, 95% CI: −1.20 to −0.56). Daily flossing was associated with a modest reduction in Shannon diversity, with no significant association for the Inverse Simpson index. Inverse associations were more pronounced among younger and lower-income adults, but not among current smokers. β-diversity differed significantly across groups, although effect sizes were minimal (Bray–Curtis R2 = 0.059%; unweighted UniFrac R2 = 0.090%). Frequent flossing was associated with reduced microbial richness and phylogenetic diversity, potentially indicating a favorable shift toward a healthier microbial community. In a nationally representative sample of U.S. adults, a higher frequency of dental flossing, particularly daily use, is associated in a dose-dependent manner with lower oral microbiome richness and phylogenetic diversity.The inverse association between flossing frequency and microbial diversity is stronger among younger adults and individuals with lower socioeconomic status, but is not observed among current smokers.Despite small effect sizes, flossing frequency is associated with statistically significant shifts in overall oral microbial community structure (β-diversity). In a nationally representative sample of U.S. adults, a higher frequency of dental flossing, particularly daily use, is associated in a dose-dependent manner with lower oral microbiome richness and phylogenetic diversity. The inverse association between flossing frequency and microbial diversity is stronger among younger adults and individuals with lower socioeconomic status, but is not observed among current smokers. Despite small effect sizes, flossing frequency is associated with statistically significant shifts in overall oral microbial community structure (β-diversity).