INTRODUCTION
Quality of life (QOL) is a crucial aspect of overall well-being because it reflects happiness and satisfaction in life. The concept of QOL is broad and complex, including subjective assessments of positive and negative factors in life [1]. Traditionally, data on disease morbidity and mortality have been key indicators for obtaining health-related information. Furthermore, health has been recognized as an important aspect of QOL, raising interest in health-related QOL (HRQoL) which refers to an individual’s subjective perception of their physical and mental health over a period [2]. By contrast, individuals with impaired HRQoL may experience poor health conditions in various aspects, heightened vulnerability to diseases, and an increased economic burden caused by diseases. Therefore, identifying the risk factors associated with impaired HRQoL is important for preventing and reducing the negative impacts on individuals and public health [3].
Current evidence suggests that combustible cigarette (CC) smoking is a risk factor associated with impaired HRQoL [4-6]. While the rate of CC smoking has declined worldwide over the past few years, the emergence of noncombustible nicotine or tobacco products (NNTPs) has recently gained popularity [7]. NNTPs are new types of nicotine products, including electronic cigarettes (ECs) that vaporize liquid containing nicotine, and heated tobacco products (HTPs) that heat tobacco without combustion [8]. The potential harm of NNTPs has often been overlooked, due to the perception that they are less harmful than CCs and can help with quitting smoking [9,10]. CC smokers who start using NNTPs in an attempt to quit smoking become tobacco users of more than one tobacco products [11]. Tobacco use of CCs and NNTPs may result in higher exposure to nicotine and chemicals compared to using a single product. Hence, it can elevate the risk of nicotine dependence and tobacco-related health consequences [12,13], which, in turn, can negatively impact HRQoL.
Considering the limited research available on the association between tobacco use and HRQoL, this study used nationwide population-based data to investigate the association between tobacco use and HRQoL among Korean men.
METHODS
1. Study Design
This study used data from the Korea National Health and Nutrition Examination Survey (KNHANES), which evaluates the nutritional and health status of the Korean population. The survey comprised nutritional questionnaires, health examinations, and interviews. The KNHANES data are in the public domain and do not contain individually identifiable information. All participants signed an informed consent form before the survey, which was approved by the Institutional Review Board of the Korean Centers for Disease Control and Prevention (IRB No.: 2013-07CON-03-4C, 2013-12EXP-03-5C, 2018-01-03-PA, 2018-01-03-C-A and 2018-01-03-2C-A). In this study, data from the KNHANES conducted between 2013 and 2020 were analyzed (Figure 1). Female participants were excluded (n=28,051) because of the low smoking rate among Korean women and the large difference between self-reported and actual smoking status. Of the 22,111 men, we excluded those who did not complete the European Quality of Life-5 Dimensions (EQ-5D) (n=2,846) and those with missing values for other variables (n=2,836). Overall, 16,429 male participants aged ≥19 years were included in the study and were classified as follows: never users (n=4,481), former users (n=6,550), CC smokers (n=4,422), NNTP users (n=267), and current tobacco users (n=709).
2. Tobacco Use Status
The tobacco use status of participants was assessed using a self-report survey. Never users were classified as individuals who had smoked less than 100 CCs and had neither smoked CCs nor used NNTPs throughout their lives. Former users were classified as individuals who had smoked more than 100 CCs or had used NNTPs at some point but were not currently using either. CC smokers were classified as individuals who had smoked more than 100 CCs throughout their lives and currently smoked occasionally or daily, but had not used NNTPs throughout their lives. NNTP users were classified as individuals who had used ECs or HTPs throughout their lives and were currently using, but had not smoked CCs throughout their lives. EC users were classified as individuals currently using ECs. HTP users were classified as individuals currently using HTPs. Current tobacco users were defined as individuals who used more than one tobacco product, including CCs and NNTPs.
3. Covariates
The demographic variables analyzed in this study included age, educational level, household income level, residential area, marital status, occupation, body mass index (BMI), and obesity status. Age was categorized into four groups: 19–29, 30–39, 40–49, and ≥50 years. Educational qualifications were categorized based on high school graduation. Household income levels were classified as either “high” or “low” based on monthly income. Participants living in rural areas, specifically in “eup” or “myeon,” were classified as rural residents, whereas those living in “dong” were classified as urban residents. Participants were categorized as either “single” or “married” based on their marital status. Homemakers and students were classified as unemployed. “Simple labor workers,” “service and sales workers,” “technical staff and equipment- and machine-operating workers and machine-assembling workers,” and “skilled workers in agriculture, forestry, and fisheries” were classified as manual workers. “Office workers” and “managers, specialists, and related workers” were classified as non-manual workers. Individuals with BMI >25.0 kg/m2 were classified as obese.
Regular physical activity was defined as engaging in more than 20 minutes of intense activity for 3 days or more or engaging in more than 30 minutes of moderate activity for more than 5 days per week. Alcohol consumption was defined as consuming alcohol at least once per month. In terms of mental health, stress status was defined as moderate or extreme levels of stress according to individuals’ self-perceived stress levels, and depression was defined as individuals who had experienced a depressed mood for more than 2 weeks throughout the past years. Participants were categorized based on a physician’s diagnosis of hypertension, diabetes mellitus, dyslipidemia, cardiovascular diseases (including myocardial infarction, angina, and stroke), and cancer (stomach, liver, colon, lung, thyroid, and other cancers) using a self-report survey.
4. Health-Related Quality of Life Measurement
The EQ-5D was used to measure the HRQoL. Developed by the EuroQol Group in the 1980s, the EQ-5D is a generic instrument to evaluate and compare factors associated with HRQoL [14]. Participants’ current health status was assessed using five domains of the EQ-5D: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. The five domains were categorized into three response levels: no problems (1), some problems (2), and extreme problems (3), generating values for 243 health conditions. The EQ-5D index score ranges between 0 and 1, with higher scores indicating better health conditions [15]. No established cut-off value for the EQ-5D index score exists to determine impaired HRQoL. In this study, EQ-5D index scores were divided into five quantiles. Participants who scored below the lowest 20% and reported some or “some problems” or “extreme problems” in the EQ-5D domains were classified as having impaired HRQoL.
5. Statistical Analysis
Data from the KNHANES were used, and integrated weights were calculated and analyzed to ensure representation of the Korean population. One-way analysis of variance was used to examine continuous variables, whereas the chi-square test was employed to analyze categorical variables. We used multiple logistic regression analysis to calculate odds ratios (ORs) and 95% confidence intervals (CI) to examine the association between tobacco use and impaired HRQoL. Four models were used to adjust for different covariates: model 1 (no covariate unadjusted), model 2 (age was adjusted), model 3 (education, household income, residential area, marital status, occupation, obesity, physical activity, alcohol consumption, and the covariate used in model 2 were adjusted), and model 4 (stress, depression, hypertension, diabetes mellitus, dyslipidemia, cardiovascular diseases, cancers, and the covariates used in model 3 were adjusted). Statistical significance was defined as P<0.05. Statistical analyses were performed using the SAS ver. 9.3 (SAS Institute Inc., Cary, NC, USA).
RESULTS
1. Baseline Characteristics
Table 1 illustrates the characteristics of 16,429 men aged ≥19 years. Among the participants, 4,481 (30.5%) were categorized as never users, 6,550 (34.5%) as former users, 4,422 (27.8%) as CC smokers, 267 (1.8%) as NNTP users, and 709 (5.4%) as current tobacco users. The mean age of current tobacco users was the lowest, and their mean BMI was higher than that of the other groups (P<0.001). Current tobacco users were mainly aged 19–29 years, above high school graduates, high-income earners, urban residents, married, manual workers, not obese, did not engage in regular physical activity, consumed alcohol at least once a month, and had a low stress status (P<0.001). Current tobacco users exhibited significantly lower prevalence rates of depression, hypertension, diabetes mellitus, dyslipidemia, cardiovascular diseases, and cancer (all P<0.001).
2. Distribution of the European Quality of Life-5 Dimensions
The mean EQ-5D index score of current tobacco users was significantly lower than that of never users (P<0.001). Among the five domains of the EQ-5D, current tobacco users reported more problems with mobility, usual activities, and pain/discomfort than never users (all P<0.001). No significant differences were observed in anxiety/depression domains (Table 2).
3. Association between Smoking Status and Impaired Health-Related Quality of Life
The multiple logistic regression analysis showed that current tobacco users had a significantly higher risk of impaired HRQoL compared with never users (model 4: OR, 1.42; 95% CI, 1.05–1.92) whereas no significant difference was observed among former users, CC smokers, and NNTP users. Moreover, compared to never users, current tobacco users reported more problems with mobility and pain/discomfort in Model 4 (all P<0.05). Compared to never users, CC smokers reported more problems with mobility, self-care, and usual activities in model 4 (all P<0.05). Compared to never users, the adjusted OR for mobility was higher in current tobacco users (OR, 2.04; 95% CI, 1.33–3.13) than in CC smokers (OR, 1.41; 95% CI, 1.16–1.71) based on Model 4. No significant differences in impaired HRQoL and problems within the EQ-5D domains were observed between NNTP users and never users (Table 3).
Among participants with a history of tobacco use, current tobacco users had a significantly higher risk of impaired HRQoL than former tobacco users (model 4: OR, 1.60; 95% CI, 1.18–2.17). Compared to former users, CC smokers had a higher risk of impaired HRQoL (model 4: OR, 1.17; 95% CI, 1.02–1.34). Additionally, compared to former tobacco users, current tobacco users reported more problems with mobility and pain/discomfort in model 4 (all P<0.05). Compared to former users, CC smokers reported more problems with mobility and usual activities in model 4 (all P<0.05). Compared to former tobacco users, the adjusted OR for mobility was higher in current tobacco users (OR, 1.84; 95% CI, 1.2–2.78) than in CC smokers (OR, 1.21; 95% CI, 1.02–1.42) based on Model 4. No significant differences in impaired HRQoL and problems within the EQ-5D domains were found between NNTP users and former users (Model 4) (Table 4).
As the KNHANES data from 2019 classified NNTP users into EC and HTP users, we examined the association of HRQoL among current tobacco users, EC users, HTP users, CC smokers, former users, and never users between 2019 and 2020. The mean EQ-5D index score of current tobacco users was significantly lower than that of EC, HTP, and never users (P<0.001) (Supplement 1). Supplements 2 and 3 show the association between impaired HRQoL and tobacco use.
4. Subgroup Analysis
Stratified subgroup analyses were performed according to age, education, occupation, residential area, household income level, marital status, regular physical activity, alcohol consumption, obesity, stress, depression, hypertension, diabetes mellitus, dyslipidemia, cardiovascular disease, and cancer (Table 5). The association of impaired HRQoL among never users and current tobacco users did not differ across most subgroups, including age, education, occupation, household income level, marital status, regular physical activity, alcohol consumption, stress, depression, hypertension, diabetes mellitus, cardiovascular diseases, and cancers (P for interaction; 0.177, 0.525, 0.394, 0.779, 0.231, 0.118, 0.486, 0.862, 0.512, 0.113, 0.547, 0.134, 0.093, respectively), except for some subgroups such as residential area, obesity, and dyslipidemia (P for interaction; 0.022, 0.021, 0.026, respectively).
DISCUSSION
This nationwide population-based study demonstrated that tobacco use was associated with impaired HRQoL in Korean men. Compared with never users and former users, current tobacco users exhibited a significantly higher risk of impaired HRQoL and reported more problems with mobility and pain/discomfort.
Previous studies have found an association between CC smoking and impaired HRQoL [16-18]. A study based on the general English population reported that smoking was negatively associated with HRQoL. Heavy smokers had a significantly higher risk of experiencing some or severe problems in all five domains of the EQ-5D compared with non-smokers [16]. A recent study conducted in China suggested that smokers had 11.65% lower average probability of having a higher HRQoL compared with non-smokers [17]. Another study based on the KNHANES revealed that current smokers had higher adjusted ORs for impaired HRQoL compared with former smokers (OR, 1.21; 95% CI, 1.21–1.21) and non-smokers (OR, 1.17; 95% CI, 1.17–1.17). Moreover, compared to former smokers and non-smokers, current smokers had more problems in all domains of the EQ-5D (all P<0.001) [18]. However, no study has examined the association between tobacco use and HRQoL. Notably, this is the first study to examine whether tobacco use is associated with HRQoL among Korean men.
The positive association between tobacco use and impaired HRQoL can be attributed to several factors. Current tobacco users are exposed to higher levels of nicotine and chemicals, which increase oxidative stress and the release of inflammatory cytokines [19,20]. These inflammatory changes can negatively affect individuals’ health status and increase the risk of tobacco-related diseases such as metabolic syndrome, respiratory diseases, and cardiovascular diseases [20-22]. The diseases resulting from tobacco use can cause difficulties in any of the five domains of the EQ-5D. Additionally, long-term nicotine intake from using tobacco products can induce the desensitization of nicotinic acetylcholine receptors in the brain and a decrease in neurotransmitter release, particularly for serotonin and dopamine [23,24]. This ultimately leads to the development of anxiety and depression [25,26], indicating that current tobacco users may be more vulnerable to these mental health issues than never users [27]. Therefore, the findings of this study showed that tobacco use has a significant impact on certain domains of the EQ-5D in relation to impaired HRQoL.
In this study, current tobacco users were shown to have a higher risk of impaired HRQoL than former tobacco users. Specifically, current tobacco users reported more problems with mobility and pain/discomfort than did former users. These findings suggest that individuals who continue to use more than one tobacco product, including CCs and NNTPs, are more likely to have impaired HRQoL than those who quit smoking. Furthermore, smokers who successfully quit smoking experience a significant improvement in their HRQoL [28,29]. Therefore, it is crucial for public health efforts to provide accurate information on tobacco use, especially regarding the uncertain perception of NNTPs as a smoking cessation tool. In addition, regulations on access to CCs and NNTPs as well as tobacco bans and pricing strategies can promote public health.
Although this study offers valuable insights, some limitations must be acknowledged. As this was a cross-sectional study, causal relationships could not be established. There is a potential for bias in cases where underlying health conditions lead individuals to adopt tobacco use. Reliance on self-report surveys introduces recall bias and the possibility of participant underestimation. The omission of nicotine levels and nicotine dependence measurements among current tobacco users calls for further research to categorize such users more comprehensively.
Despite these limitations, this study had several strengths. It harnessed a large, representative dataset from the KNHANES, which enhanced the reliability and generalizability of the results. The self-reported survey data enabled the specific classification of current tobacco users. The study’s utilization of the validated EQ-5D facilitated a comprehensive evaluation of the association between tobacco use and HRQoL. Furthermore, adjustments for various confounding factors yielded statistically significant results, which were attributed to the analysis.
In conclusion, use of CCs and NNTPs was associated with impaired HRQoL in Korean men. Therefore, further interventions for lifestyle modification and smoking cessation treatments are required to reduce the risk of impaired HRQoL among current tobacco users. Additionally, continuous HRQoL assessments for current tobacco users are recommended to evaluate the effectiveness of new regulations in reducing health disparities and improving overall HRQoL.
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