Background
Periodontitis is a common chronic inflammatory disease with a high incidence of 50% [
1], which increases the risk of systemic diseases, such as diabetes, cardiovascular diseases, Alzheimer's disease, and mental disorders [
2,
3]. The important role of inflammatory bimarkers, such as cortisol, TGF-1β and TNF-α, in the pathogenesis of periodontitis has drawn the attention to the systemic impact of periodontitis and its potential relationship with other diseases [
4,
5]. More recently, psychological conditions, most notably depression, have been shown to be associated with periodontitis. According to the Global Burden of Disease Study, depression prevalence in the United States ranges from 11 to 21% and becomes the leading cause of disability-adjusted life-years (DALYs) worldwide [
6,
7]. Due to the high burden of the two diseases, more attention has been paid to explore the potential association between periodontitis and depression and further prevent their comorbids in primary care.
At present, there were a large number of studies, including epidemiological evidence and the potential biological mechanisms, demonstrating the linkage between periodontitis and depression [
4,
5,
8]. In addition, there was an overlap between risk factors for periodontitis and depression, including smoking, drinking, physical activity, and poor oral hygiene practices [
4]. Further evidence indicated that cigarette smoking was responsible for periodontitis [
9], and it also can predict the severity and progression of depression [
8,
10]. Similarly, drinking also has a minor but significant association with periodontal health, and heavy drinking frequently co-occurs with depression [
11,
12]. Considering the fact that periodontitis and depression are both multifactorial and co-occurring disorders [
13], further investigation into the relationship of smoking, drinking and depression with periodontitis risk, may help understand periodontitis and its comorbids conditions and further contribute to the prevention of periodontitis and depression.
Interaction analysis is a useful approach for examining multiple modifiable exposure factors that play a role simultaneously or interact with one another on disease risk [
14]. It has been widely used in gene–gene and gene-environment studies but less frequently used in periodontitis. According to recent literature, smokers with stage III periodontitis had increased stress than non-smokers [
15]. Similarly, patients with chronic periodontitis, smoking habits and depression had the highest levels of salivary cortisol levels [
16]. It has also been reported that populations with both drinking and smoking had higher risk for developing periodontitis than those with either factor alone, indicating that they have interactive effects on periodontitis risk [
17]. Despite the importance of understanding how these factors can interact on periodontitis risk, most previous epidemiological studies have focused only on single health behavior in isolation. There is no comprehensive interaction analysis on multiple lifestyle factors. Therefore, it is of clinical significance to investigate the interactive association between these reversible health risk factors and periodontitis.
This study aimed to investigate the independent and interactive effects of smoking, drinking and depression on the prevalence of periodontitis based on the National Health and Nutrition Examination Survey (NHANES, 2009–2014).
Null Hypothesis was: There is no significant influence, either individually or collectively, of smoking, drinking, and depression on the risk of periodontitis prevalence.
Discussion
This is the first systematic examination of the interaction between depression, smoking, and alcohol consumption on the prevalence of periodontitis using a large US population. In the overall population and within gender subgroups, we observed significant multiplicative interactions between smoking-depression and smoking-drinking. In the depressed population, smoking significantly increased the prevalence of periodontitis by 1.29-fold in the youth group compared with non-smoking. Moreover, the co-occurrence of smoking and heavy alcohol consumption exhibited a significant elevation in the prevalence of periodontitis. Based on the findings of this study, our null hypothesis was rejected.
Our study found that cigarette smoking served as a risk factor for periodontal diseases, as previously reported [
9]. Results showed that both former and current smokers were more likely to develop periodontitis than non-smokers in the general population (PHQ-9 score < 10). The proposed explanation was that smoking effects on inducing systemic inflammation can continue for months or years despite the fact that cigarette smoke extracts have been removed from the body after smoking cessation [
9]. This result was inconsistent with previous studies, which indicated no significant difference between never-smokers and former smokers regarding periodontitis risk [
28,
29]. The heterogeneity of research can be attributed to different time frames for evaluating smoking status. It has been further reported that until approximately 6 years after quitting smoking, the smoking-related risk for periodontitis will diminish and approach to that of never-smokers [
30].
To our knowledge, this is the first time that the interaction between smoking and depression has been indicated in periodontitis. Previous evidence have demonstrated that psychological stress and smoking may serve as mediators for the prevalence of periodontal diseases [
31]. Both biological mechanisms, such as inflammatory responses [
9] and behavioral theories have been proposed to explain how smoking and depression independently influenced periodontitis. The mechanisms underlying the correlations between smoking and periodontitis shared similarities with those linking depression to periodontitis [
9]. One proposed explanation for this synergistic effect is that smokers with a history of depression can have a prolonged and/or augmented inflammatory response since the anti-inflammatory response capability may be downregulated by depression condition. Then, a hyper-inflammatory response can be reinforced by smoking status, thereby accelerating the progression of periodontitis [
9]. Considering our findings, more attention should be paid to the screening and prevention of periodontitis in depression subjects and depression in periodontitis patients by collecting comprehensive information regarding the smoking history and depressive symptoms.
Further results showed that the smoking-depression interaction exhibited consistency across various age and gender cohorts. This interaction was only significant in males not females due to the exceptionally low smoking rates among women in this study. Additionally, depressed men frequently failed to maintain healthy behaviors, such as smoking cessation [
32]. On the other hand, this association was consistent in both young and aged populations. Therefore, regardless of an individual's age, smoking consistently has adverse impacts on periodontitis, regardless of the duration of smoking, whether it is of a short-term or long-term nature.
A dose-dependent relationship was identified between drinking and periodontitis, as well as between smoking-drinking interaction and periodontitis. This finding aligns with previous research, indicating the association between cigarette smoking and increased periodontitis risk with alcohol assumption increment [
17]. The potential hypothesis is that the dysfunction of immune cells, specifically T-cells and neutrophils, may be responsible for the cumulative effects observed with excessive alcohol intake surpassing a specific threshold [
33]. Subsequently, the risk for infectious complications including periodontitis can be elevated due to the excessive alcohol intake [
11]. Overall, these results underscore the adverse effects of alcohol consumption itself, as well as its confounding adverse effects when combined with other factors such as smoking on periodontitis progression. This highlights the significance of limiting cumulative alcohol intake from both the individual and combined effects.
Our study has some strengths. First, we analyzed a large-scale population and examined the complicated interactive relationship between different influencing factors rather than focus on only one single factor. Second, data from the NHANES were selected using a complex, multi-stage probability sampling design fully representative of the general population across the United States. Third, multiple confounding factors were considered in this study, including sociodemographic characteristics and history of diabetes. There are some limitations to this study. First, no causality can be inferred from the data due to the cross-sectional nature of the study. As with other cross-sectional studies, the temporal relationship cannot be established considering the long-term variables (e.g., periodontitis, smoking) and the short-term variables (e.g., drinking and depression). Therefore, further study is needed to solve geographic restrictions from a large multinational population. Second, our study utilized CAL as the sole criterion for grading the severity of periodontitis, without considering other factors like aggressive tooth brushing and periodontal trauma. This may lead to some bias in the patients inclusion, which could be improved by designing comprehensive and detailed epidemiological surveys. However, it is important to consider that such improvements often come with higher survey costs and longer research cycles, therefore a balance needs to be achieved between the accuracy, cost, and time in the future survey designs.
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