Does tooth brushing protect from atrial fibrillation and heart failure?

Atrial fibrillation (AF) is the most common cardiac arrhythmia in the general population, and it is associated with an increased risk of stroke, congestive heart failure (CHF), death, and cognitive dysfunction.1,,–4 CHF is a frequent cause of hospital admission and death.5,–7 Both disorders often occur together, have similar underlying risk factors, and their combination strongly correlates with increased morbidity and mortality.8,–10 Common risk factors include older age, elevated blood pressure, coronary artery disease, valvular heart disease, and diabetes mellitus.11,–13 Inflammation has also been associated with both AF and CHF.14,–16 Observational and histopathological studies have shown that an increased inflammatory state, mainly measured by inflammatory biomarkers, not only increases the likelihood of AF initiation and progression, but also the risk of developing and worsening CHF.17,–19 Poor oral hygiene is an established risk marker for cardiovascular disease.20 It has been hypothesized that poor oral hygiene may lead to transient bacteremia, which may cause systemic inflammation. However, little information has been available on the relationships of poor oral hygiene with the incidence of AF and CHF. In this issue of the European Journal of Preventive Cardiology, Chang et al.21 report on the associations of various markers of oral hygiene care with AF and CHF using data from the National Health Insurance System-National Health Screening Cohort in Korea. Subjects were enrolled if they participated in medical health screening programs. Exclusion criteria were previous history of AF, CHF, or valvular heart disease, or missing data on oral health status, leaving a total of 161,286 subjects for this analysis. After a median follow-up of 10.5 years, 4911 (3.0%) and 7971 (4.9%) individuals developed AF or had CHF, respectively. In multivariable analyses, frequent tooth brushing (≥3 times/day) was associated with lower risks of incident AF (adjusted hazard ratio (aHR) 0.90; 95% confidence interval (CI), 0.83–0.98) and CHF (aHR 0.88; 95% CI, 0.83–0.94). Subjects who had a high number of missing teeth (≥22) were at higher risk of HF (aHR 1.31; 95% CI, 1.11–1.55). None of the other associations were statistically significant. In subgroup analyses, no interactions were found for the relationships of number of tooth brushings with incident AF and HF, stratified by demographic characteristics and comorbidities. The researchers conclude that improved oral hygiene care may help to reduce the risk of developing AF and CHF. The strengths of this study presented by Chang et al.21 are the large sample size, with over 160,000 individuals included in the study, the large number of outcome events, and the long follow-up duration. This allowed the investigators to carry out meaningful analyses and adjust the multivariable models for many covariates, such that some of the confounding could be controlled. Nonetheless, this study has some limitations that need to be acknowledged. First, the study had a retrospective design, which may have introduced selection bias. Residual confounding is an issue in all observational studies. In multivariable analyses, most relationships of oral hygiene indicators with AF and CHF either lost statistical significance or were substantially attenuated. This suggests that the observed associations are heavily confounded by other covariates, and it is unclear whether all known and unknown confounders have been included in the multivariable models. Second, only individuals from Asia were included in the study, and the generalizability of the results is unclear. Third, the outcomes of AF and CHF were investigated through administrative data, and systematic electrocardiograms or echocardiographic measures were not available. Fourth, level of education, marital status, and information on inflammatory biomarkers, such as C-reactive protein, were not available. Marital status and education have been especially associated with both oral hygiene and outcome measures, and, therefore, may have confounded the observations.22,,–25 Fifth, information about oral hygiene indicators, including the number of tooth brushings, dental visit for any reasons, and professional dental cleaning were collected through self-reported questionnaires, which could have introduced recall bias. Finally, indicators of oral hygiene and associated risk factors may change over time, such that time-updated analyses may have further improved the interpretability of the results. In conclusion, Chang et al.21 found an association of poor oral hygiene with incident AF and CHF. The causality of these associations is unclear, and it is certainly too early to recommend tooth brushing for the prevention of AF and CHF. While the role of inflammation in the occurrence of cardiovascular disease is becoming more and more evident, intervention studies are needed to define strategies of public health importance.