Periodontal disease is associated with the risk of cardiovascular disease independent of sex: A meta-analysis

Objectives Studies have established a link between periodontal disease and cardiovascular disease (CVD), but it is unclear whether there is a sex difference in their association. Methods The PubMed, Embase, and Cochrane databases were searched until June, 21 2022. Cardiovascular outcomes included any CVD, myocardial infarction (MI), coronary heart disease (CHD), or stroke. Studies reported the prevalence of CVD in patients with periodontal disease and the relationship between periodontal disease and CVD. The study is registered with PROSPERO (CRD42022333663). The level of evidence and recommendations is assessed by the Grading of Recommendations for Assessment, Development and Evaluation (GRADE). Results Twenty-six studies were included. In patients with periodontal disease, the prevalence of CVD was 7.2% [9 studies; 95% confidence interval (CI): 2.7–13.6%], and prevalence for CHD, hypertension, stroke, and heart failure was 6.6, 25.3, 1, and 1.1%, respectively. There was a significant association between periodontal disease and CVD in men [odds ratio (OR) = 1.22; 95% CI: 1.12–1.34] and women (OR = 1.11; 95% CI: 1.05–1.17), with no significant sex difference (P > 0.05). Conclusion Cardiovascular disease is relatively common in patients with periodontal disease, and an increased risk of CVD is associated with periodontal disease independent of sex. Interventions targeting periodontal disease may be beneficial for CVD. Systematic review registration https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42022333663.


Introduction
Cardiovascular disease (CVD) remains the leading cause of death, accounting for approximately one third of all deaths worldwide. The global incidence of CVDs is 10∼30%, showing a gradually increasing trend (1)(2)(3). China has the highest cardiovascular mortality rate, followed by India, the Russian Federation and the United States of America (4). However, periodontal disease is increasingly becoming one of the major obstacles to optimal outcomes for patients with cardiovascular disease (CVD) (5).
Periodontal disease is one of the most common inflammatory diseases in humans that destroys hard and soft tissues around the tooth, resulting in tooth loosening and loss (6). Severe periodontal disease affects 10.8% of the world's population and is the sixth most common disease worldwide, with more than 700 million people suffering from severe periodontal disease (7). Periodontal disease can cause inflammation of periodontal tissue but also produce inflammatory mediators and can products that can cardiovascular health through blood circulation (8). In recent decades, longitudinal studies have revealed a firm link between periodontal tissue and an increased risk of CVD. However, no study has systematically studied the prevalence of CVD in patients with periodontal disease. Moreover, female sex is considered to have a protective effect on the incidence and development of CVD (9,10). However, whether there is a sex difference in the relationship between periodontal disease and the risk of CVD remains unexplored. Hence, the present study aimed to (i) systematically evaluate the prevalence of CVD in patients with periodontal disease, and (ii) examine the sex-specific association of periodontal disease with CVD.

Protocol registration
The study has been registered with PROSPERO (International Registry of Prospective Systems Review: https: //www.crd.york.ac.uk/PROSPERO/ number: CRD42022333663). This meta-analysis was conducted in accordance with PRISMA 2021 guidelines for systems evaluation and meta-analysis 1 (11) (Supplementary Table 1).

Search strategy
The PubMed, Embase, and Cochrane Library online databases were searched up to June 25, 2022 with no language restriction. The MeSH search items and keywords were as follows: ["periodontal disease" (MeSH) OR "furcation defects" OR "gingival diseases" OR "peri-implantitis" OR "periapical diseases" OR "periodontal atrophy" OR "periodontal cyst" OR "periodontitis" OR "tooth migration" OR "periodontitis" OR "tooth mobility" OR "tooth loss"] AND ["cardiovascular diseases" (MeSH)]. The detailed search strategy is shown in Supplementary Table 2.

Study selection
After a database search, the retrieved studies were imported into Endnote X9 software (Thomson Reuters, New York, NY, USA). The title and abstract were selected by one author (YL) and verified by a second author (QH). Before data extraction and quality assessment, the whole article was qualified. The authors reached a consensus on the included studies, and the differences were resolved through in-depth discussion. Before the database search, a data extraction form was developed to identify key study information, including demographics, data sources, exclusion criteria, follow-up periods, diagnostic criteria, and outcome measures.
Strict eligibility criteria guided the search to ensure relevant study inclusion, reduce heterogeneity and increase the power of the results. The inclusion criteria for epidemiological studies were as follows: (1) adult's patients with periodontal diseases (including periodontitis and gingivitis); (2) reported prevalence of CVD in patients with periodontal diseases; and (3) cross-sectional, retrospective, or prospective cohort and randomized controlled trials studies. Studies with sample size <10,000 were excluded.
Additionally, eligible criteria for studies of the relationship between periodontal disease and CVD were as follows according to the PICOS: (1) Types of participants: adults; (2) Exposure and comparator: patients with periodontal disease vs. without periodontal disease; and (3) Outcomes: sex-specific association between periodontal diseases and CVD. (4) Types of studies: retrospective or prospective cohort, case-control and randomized controlled trials studies. Studies were excluded from the review if they met any one of the following criteria: (1) Protocols, reviews, conference abstracts, or animal studies; (2) Studies with unavailable data even after contacting the corresponding author for further information.
The Newcastle-Ottawa quality scale (NOS) was used to quantify the quality of cohort studies, with a score above six regarded as acceptable quality. We evaluated the quality and strength of the evidence using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) method, which evaluates each outcome according to the recommended rating assessment, development and evaluation. Two authors (QH and YL) evaluated the quality of evidence of each result, providing an evidence profile table by GRADE profiler software. The results were described in the outcome measure type section, whose footnotes were used to justify any decision to reduce or improve the quality of the evidence. Flowchart of the study selection for the meta-analysis of an association between periodontal disease and cardiovascular disease [adapted from Moher et al. (67)].

Statistical analysis
We treated RRs and HRs as equivalent to ORs, and pooled the summary ORs with corresponding 95% CIs using the inversevariance method (12). Random effect meta-analysis was performed for the overall as well as separate CVD outcomes.
Heterogeneity was evaluated using the Higgins I-squared (I 2 ) statistic (30,50, and 75% represent low, moderate, and high heterogeneity, respectively) (13). Publication bias was addressed by the funnel plot, and Egger's and Begg's tests. To appraise the robustness and reliability of the primary study outcomes, we also carried out sensitivity analyses by omitting each study in turn. The statistical analysis was performed by RevMan software, version 5.4.1 (The Cochrane Collaboration, Nordic Cochrane Center, Copenhagen, Denmark) and Stata software, Version 16.0 (Stata Corp. LP, College Station, TX, USA). P < 0.05 double-sided was considered statistically significant.

Sex-specific association between periodontal disease and stroke
For eight studies that reported an association between periodontal disease and stroke, there was a higher risk of Forest plot of the prevalence of cardiovascular disease in patients with periodontal disease. In the forest plot, the diamond indicates the pooled estimate. Red boxes are relative to study size and the black vertical lines indicate 95% CIs around the effect size estimate.

Publication bias and sensitivity analysis
As shown in Supplementary Figure 2, although some presence of bias was found by funnel plots, Egger's test (P > 0.1), and Begg's test (P > 0.1) showed no significant publication bias. Sensitivity analysis by omitting each study showed that our results were stable and reliable, with a range from 1.09 (95% CI: 1.03-1.15) to 1.14 (95% CI: 1.05-1.24) for the relationship between periodontal disease and CVD in females, and 1.24 (95% CI: 1.12-1.38) to 1.29 (95% CI: 1.15-1.43) for the relationship between periodontal disease and CVD in males (Supplementary Figure 3).

Quality assessment
The GRADE tool was used to evaluate the quality of evidence. All the included studies were observational studies; thus, so the initial level of evidence was low (42). Ultimately, the risk of CVD was evaluated as very low certainty (Supplementary Table 5).

Major findings
The present meta-analysis showed that the pooled prevalence was 7.3% for CVD, 6.6% for CHD, 25.3% for HP, 1% for stroke, and 1.1% for HF among periodontal disease patients. Moreover, a significant association between periodontal disease and the risk of CVD was found independent of sex, with a summary OR of 1.22 (95% CI: 1.12-1.34) for females and 1.11 (95% CI: 1.05-1.17) for males. To the best of our knowledge, this article is the first to explore the sex-specific association of periodontal diseases and CVD.
Consistent with results of a previous meta-analysis (43), our study also showed that periodontal disease is associated with the risk of CVD. More importantly, our meta-analysis also showed that this association remains in both men and women, without sex differences. To ensure the rigor of our results, necessary analysis for potential publication bias was conducted, and the final results were reliable. CVD has always been shown to have a greater possibility of secondary oral problems. As Lazureanu et al. showed in their research on the prevalence of periodontal disease in patients with CVD (44), 77.5% of the 147 patients with CVD developed periodontal disease, implying a high incidence of periodontal disease among patients with CVD. However, few related studies have explored the incidence of CVD in patients with periodontal disease. Our study indicated that the prevalence of CVD in patients with periodontal disease reached 7.2%, suggesting that the occurrence of CVD is relatively common in patients with periodontal disease. As a result, we hypothesize that there may be a significant association between periodontal disease and CVD, which was also confirmed in our subsequent analysis about the association between periodontal disease and CVD.
Age is a vital risk factor for both CVD and periodontal disease. In subgroup analyses, younger patients with periodontal disease were shown to have an increased risk of CVD, with a prevalence of 23.8% in the younger group (age <45 years) versus 7.5% in older one (age ≥45 years). This was consistent with Joshipura et al. (34) who reported a stronger effect for younger men than for older men (≤55 years: RR = 2.17; 95% CI: 1.22-3.84 vs. >55 years: RR = 1.21; 95% CI: 0.92-1.59). Similarly, in a casecontrol study, four cases of clinical attachment loss of 4.5 to ≤6 mm were associated with a significantly increased risk of stroke (OR = 3.43; 95% CI: 1.39-8.50) in men ≤60 years, while there was no statistical significance in younger men (age >60 years) (OR = 1.71; 95% CI: 0. 65-4.5). Men who were susceptible to periodontitis were shown to develop periodontal destruction earlier than those who were not. Thus, there is a stronger association between periodontitis and cerebrovascular disease in young men than in older men, which may further support the hypothesis of proinflammatory susceptibility.

Potential mechanism
Our results showed that periodontal disease is strongly associated with a high risk of CHD, MI, and CVD, suggesting that periodontal disease is significantly associated with CVD. Systemic inflammation may be the core mechanism to explain the association between periodontal disease and the increased risk of CVD. Considerable studies have shown that inflammation is a predisposing factor or cardiovascular disease (45,46), and patients with periodontal disease have been confirmed to have a high CRP lever as well as other inflammatory markers in the circulation (47,48), indicating that it may lead to systemic inflammation and thus induce the development of CVD. In addition, oral pathogens such as Porphyromonas gingivalis (P. gingivalis) can reach the blood by crossing the gingival epithelial-conjunctival barrier and vascular endothelial cells, thus aggravating the inflammation and immune response in the original atherosclerosis in blood vessels (49)(50)(51)(52). In addition, one animal study had found that P. gingivalis can enhance the expression of high mobility group box 1 (HMGB1) in mice after myocardial infarction. HMGB1 is a nuclear protein that induces inflammation (53). Therefore, it can be inferred that the increased risk of myocardial infarction caused by periodontal disease may be related to HMGB-1. One study showed that P. gingivalis infection and invasion can accelerate programmed cell death and the role of myocardial matrix metalloproteinases 9, which is not conducive to the recovery process of myocardial infarction prognosis, and may eventually lead to cardiac rupture (54). The increased risk of stroke may be due to decreased vascular endothelial function in the gingival tissue after infection with periodontal disease. The damage of vascular function may be caused by the basic interaction between oxidative stress and nitric oxide induced by periodontal disease (55).

The effect of sex
Although our results showed that there was no difference between periodontal disease and CVD in different sexes, sex differences were shown in the coronary artery disease subgroup analysis, where men with periodontal disease had a higher risk of coronary artery disease than in women. In addition, a prospective cohort showed that the incidence of stroke in men was significantly higher than that in women in the total population and among the periodontal disease groups (56). This may arise from the expression of Y-encoded genes and the lack of cardiovascular protective effects of estrogen, leading to male-specific cardiovascular events.
However, studies have also showed that female periodontal disease patients may have a higher risk of several CVDs. For example, an observational study showed that women with periodontal disease were 108% more likely to develop CVD (OR = 2.08, 95% CI: 1.47-2.94), which was higher than that of male periodontal disease patients (OR = 1.34, 95% CI: 1.15-1.57) (23). As a result, the sexspecific association between periodontal disease and CVD may be different in various types of CVDs. The mechanisms of how sex affects the relationship between periodontal disease and CVD are complex and still unclear, thus, further analysis is needed in the future. However, close monitoring of CVD in patients with periodontal disease is necessary in both men and women.

Clinical implications
Considering the proven association between CVD and periodontal disease, early examination and treatment for periodontal disease patients may play an important role in preventing the occurrence of CVD, which needs to be highly valued in daily clinical work. Additionally, treatment of periodontal disease may prevent the occurrence of CVD, and may also improve the status of CVD to some degree. As shown by Vidal et al. (57), periodontal therapy was able to attenuate arterial stiffness and reduce circulating inflammatory markers. Moreover, periodontal treatment with subunit-microbial doses of doxycycline could increase the level of serum apolipoprotein A and high-density lipoprotein, reduce total cholesterol levels, and further reduce the risk of cardiovascular events (58,59). As a result, periodontal disease therapy may be a therapeutic target for reduce the risk of CVD, and further relevant research is needed. However, it is interesting to note that periodontal pathogens are found in the interdental spaces even in young people with healthy periodontitis. The interdental health is thought to be closely related to cardiovascular diseases (60-62), therefore, the oral health of the interdental space should be promoted during adolescence to prevent periodontal disease and thus cardiovascular disease. Traditional daily methods to maintain oral health between teeth by destroying biofilms are still not effective enough. Studies have shown that using calibrated interdental brushes to clean teeth every day can reduce interdental bleeding, inhibit periodontal pathogens, and re-establish symbiotic microflora. and reduce interdental inflammation (63,64). These findings suggest that adherence to interdental cleanliness may be an effective way to help maintain optimal oral health, thereby preventing the emergence of periodontal disease and ultimately reducing the risk of cardiovascular disease. In addition, one study had shown that daily use of mouthwash can also help prevent periodontal disease (65).

Study limitations
There were still some limitations in present study. First, periodontal examination may be a more objective reflection of periodontal health than a self-reported diagnosis of periodontitis (66), but some of our included studies identified periodontal diseases by self-report. Second, some of the included studies were retrospective, which may have introduced recall bias, thus, further prospective studies are needed to confirm our results. Third, a high degree of heterogeneity was observed in our results due to the variation in the characteristics of the study population and study design. Finally, studies included in this meta-analysis are observational studies, however, observational studies cannot completely avoid some potential confusions, and the quality of evidence is not high.

Conclusion
The findings of this study suggest that CVD is common in patients with periodontal disease. Periodontal disease is associated with an increased risk of CVD independent of sex. Further trials are required to assess the effect of periodontal intervention on the CVD incidence.

Data availability statement
The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found in the article/ Supplementary material.

Author contributions
QD, YL, and QH contributed to the study concept and design and revised the draft. QL, XY, JC, ML, and ZY performed the search strategy and contributed to database research, acquisition of data, and statistical analyses. All authors participated in data analysis, reviewed, and approved the final manuscript.