This study investigated the association between the number of remaining teeth and hs-CRP, a marker of systemic inflammation, among Korean adults aged 65 years and older using data from the first year (2022) of the Ninth KNHANES. Hierarchical multiple linear regression analyses showed that age, family composition, diagnosed dyslipidemia, and the number of remaining teeth were significantly associated with log-transformed hs-CRP levels. In particular, older adults with fewer than 20 remaining teeth exhibited significantly higher log-transformed hs-CRP levels than those with 20 or more remaining teeth (B = 0.176, p = 0.004).

The present findings are consistent with previous Korean studies reporting an association between oral health and systemic inflammatory status. Son and Lee [12] reported that periodontal disease was significantly associated with moderate hs-CRP levels (1–3 mg/L) after adjustment for demographic and health-related factors. In addition, Cho [13] reported that individuals with 0–23 remaining teeth had higher odds of having an hs-CRP level ≥1.23 mg/L than those with 24 or more remaining teeth, which was consistent with the present finding that fewer remaining teeth were associated with higher log-transformed hs-CRP levels.

Although the present findings are consistent with previous Korean studies [12,13], they extend the existing evidence in several important ways. While previous studies included adults across a broader age range, this study focused exclusively on adults aged 65 years and older. This age group is of particular importance because cumulative tooth loss, an increased burden of chronic inflammation, and various age-related health conditions frequently coexist. Furthermore, the present study evaluated the association between the number of remaining teeth and hs-CRP levels after sequential adjustment for demographic characteristics, health-related behaviors, and health conditions. Consequently, these findings provide further evidence supporting an association between the number of remaining teeth and hs-CRP levels among older Korean adults.

These findings are also broadly supported by previous international studies conducted in diverse populations, although the strength and direction of the observed associations have varied. In older adults from the UK and USA, Kotronia et al. [15] reported that tooth loss was associated with higher levels of CRP. Similarly, Holmlund et al. [16] found an inverse association between the number of remaining teeth and inflammatory markers, including CRP, among elderly Swedish adults. More recently, Wu et al. [17] reported that hs-CRP partially mediated the association between tooth loss and mortality in a Chinese cohort, suggesting that systemic inflammation may partly contribute to the association between tooth loss and mortality. In addition, Berger et al. [18], using data from the UK Biobank, reported that higher hs-CRP levels were associated with several indicators of poor oral health, including tooth loss, dentures, bleeding gums, and loose teeth, and provided evidence suggesting that systemic inflammation may also contribute to poor oral health. Collectively, these findings support a close relationship between oral health and systemic low-grade inflammation across diverse populations and suggest that this relationship may be complex and potentially bidirectional.

Although tooth loss is partly a consequence of aging, it may also reflect the cumulative effects of long-standing periodontal disease and chronic oral inflammation [19,20]. Periodontal disease induces persistent inflammation of the periodontal tissues, and inflammatory mediators released locally may enter the systemic circulation, thereby contributing to systemic inflammatory responses [21]. Therefore, the number of remaining teeth may serve as a potential indicator of systemic inflammatory status in older adults. Importantly, however, the number of remaining teeth is not a direct measure of periodontal inflammation, and the observed association should not be interpreted as evidence that tooth loss itself directly causes systemic inflammation.

Older adults with fewer remaining teeth are also more likely to experience impaired masticatory function, which may restrict food choices. Reduced consumption of fruits, vegetables, and fiber-rich foods, together with increased reliance on soft or carbohydrate-rich foods, may contribute to nutritional imbalance and subsequently promote chronic systemic inflammation [22,23]. Thus, the association between tooth loss and hs-CRP may reflect not only the inflammatory consequences of oral disease but also pathways involving impaired mastication and dietary changes.

Age was positively associated with log-transformed hs-CRP levels, consistent with previous studies reporting that chronic low-grade inflammation increases with advancing age [3,24]. Age-related alterations in immune function are accompanied by increased production of pro-inflammatory cytokines, a phenomenon commonly referred to as inflammaging.

Family composition was significantly associated with log-transformed hs-CRP levels. Older adults living alone had significantly lower log-transformed hs-CRP levels than those living with others. This finding was unexpected because living alone has been associated with several adverse health and behavioral outcomes among older adults. Previous studies have reported that older adults living alone may be more likely to experience depression, malnutrition, physical inactivity, and difficulties in health management [25–27]. However, the mechanisms underlying the inverse association observed in the present study remain unclear. Differences in health behaviors, socioeconomic characteristics, health status, selection effects, or other unmeasured factors may have contributed to this finding. Further studies are needed to determine whether and how living arrangements influence systemic inflammation among older adults.

Dyslipidemia was significantly associated with hs-CRP levels. Dyslipidemia is a well-established risk factor for cardiovascular disease, and abnormal lipid metabolism has been linked to vascular inflammation [28]. However, in both the univariate and multivariable analyses, participants without diagnosed dyslipidemia exhibited significantly higher hs-CRP levels than those with dyslipidemia (Model 4: B = 0.236, p = 0.004). A possible explanation is that participants diagnosed with dyslipidemia may have been receiving lipid-lowering therapy, particularly statins. In addition to their cholesterol-lowering effects, statins exert anti-inflammatory effects by improving endothelial function and reducing circulating hs-CRP levels. Consequently, individuals receiving appropriate medical treatment may have lower inflammatory marker levels than those without a diagnosis. Nevertheless, medication use was not included in the present analysis, and treatment status, disease duration, and treatment adherence could not be evaluated. Therefore, the potential role of lipid-lowering therapy remains speculative. Further studies incorporating detailed medication data are warranted to clarify this association. The unexpected inverse association should therefore be interpreted cautiously rather than as evidence of a protective effect of dyslipidemia.

In contrast, BMI was not significantly associated with hs-CRP levels in this study. This finding differs from previous studies conducted in general adult populations that reported positive associations between BMI and hs-CRP [29,30]. One possible explanation is that the present study focused exclusively on older adults. Aging is accompanied by sarcopenia, changes in body composition, and alterations in fat distribution, which may limit the ability of BMI to accurately reflect adiposity and metabolic risk in older populations. Future studies should therefore consider additional measures, such as waist circumference, body fat percentage, and indicators of sarcopenia, to provide a more comprehensive assessment of body composition.

This study has several limitations. First, because the study employed a cross-sectional design using KNHANES data, causal relationships between the number of remaining teeth and hs-CRP levels cannot be established. Second, although hs-CRP is a widely used biomarker of systemic inflammation, its levels may be influenced by acute infection, medication use, dietary factors, and other chronic diseases, all of which could not be fully controlled in the present analysis. Third, although the number of remaining teeth is an objective measure of oral health, it does not fully capture other clinically relevant oral conditions, such as periodontal disease severity, denture use, or masticatory function. Fourth, the explanatory power of the final regression model was relatively low (R²=0.060), indicating that the included variables explained 6.0% of the variance in log-transformed hs-CRP levels. This may reflect the multifactorial nature of systemic inflammation and the presence of unmeasured factors.

Despite these limitations, this study has important strengths. By utilizing nationally representative KNHANES data, the findings are likely to be generalizable to the older Korean population. Furthermore, the study demonstrated that the number of remaining teeth was independently associated with systemic inflammatory status, highlighting the potential importance of oral health in promoting healthy aging. Future longitudinal studies incorporating additional relevant biological, behavioral, and oral health factors are needed to clarify the temporal and causal relationship between tooth loss and systemic inflammation and to determine whether interventions aimed at preventing tooth loss or improving oral health can reduce systemic inflammation.