Unlike aloneness that is perceived as an emotionally neutral state, loneliness is often accompanied by negative feelings, such as sadness and hopelessness [1]. Loneliness, if chronic, carries a serious health risk, both physically and mentally [2]. There is ample evidence on negative health effects of loneliness [3]. Loneliness was associated with increased risks of cardiovascular disease [4], coronary heart disease, stroke [3], worse physical functioning, mental health [5,6], and suicidal ideation [7]. Further-more, loneliness was linked with increased risk for all-cause mortality [6,8–11]. Given the clinical significance of the loneliness problem, its prevalence and risk factors will merit a close examination [12].

The prevalence of loneliness varied widely across countries and age groups [13]. It was 10.5% in German adults aged 35-74 years [14] and 39% among people aged 75 years and older in Finland with 5% feeling lonely, either often or always [15]. Moreover, loneliness appears to have become an issue of great magnitude during the 2019 coronavirus disease (COV-ID-19) pandemic due to restrictions imposed on social contact; a survey of a large, nationally representative sample in April-May 2020 revealed that 35.9% of residents in the United Kingdom (UK) sometimes or often felt lonely [16]. Another study estimated that 27% of UK adults were lonely in early 2020 [17].

Loneliness is such a highly prevalent condition in many countries that researchers termed it a growing public health problem [18] and suggested that it should be incorporated as part of general health surveillance [13]. Unlike these assessments in other developed countries, the prevalence of loneliness in Korea was estimated to be just 4.1%, according to a 2019 study based in two cities (Paju city, Daegu Metropolitan City) and the Gangnam district of Seoul [19]. In this context, there is an urgent need to understand the magnitude of loneliness in Korea based on a nationally representative sample.

To help address the growing problem of loneliness, numerous studies have documented its risk factors [20,21]. Loneliness either increased [15] or decreased [17] with advancing age. In addition, the risk of loneliness is known to increase with low level of education and poor financial situation [15]. Another significant predictor of loneliness based on data from around the world was marital status [22,23]. Single adults were more stressed due to loneliness [24]. In addition, negative changes in marital status were associated with increased risk of loneliness [15,20]. Death of a spouse was a common cause of loneliness and was linked to more depressive symptoms for older adults [25,26]. There is some indication in the literature that the deleterious impact of dissolution of marriage on loneliness may differ between men and women [21]. However, under-standing is limited, especially in the Korean population. Therefore, this cross-sectional study aims to estimate the prevalence of loneliness in Korean adults aged 30 years and older and to examine risk factors for loneliness with a particular focus on marital status using publicly avail-able nationwide survey data. The results of this study will help develop social support measures to ameliorate loneliness in the general population.

In the 2021 KOWEPS, a total of 9,442 participants (4,066 males and 5,376 females) answered to the question of how many days they felt they were lonely as if they were alone in the world during the past week (Table 1). 20.2% of the study population were estimated to have felt lonely at least occasionally (one day a week). 51.7% of the study population were female and 24.3% were aged 50-59 years old. 43.8% attained junior college or higher levels of education. 71.1% were married. 18.8% were from low income households. 52.5% were salaried workers and 35.6% economically inactive.

31.2% of women in the study sample felt lonely at least one day a week compared to 21.4% of men (Table 2). The proportion of respondents who were lonely increased with advancing age and 46.8% of respondents aged 80 years and older reported being lonely. 42.6% of people with no or only primary education were lonely. 52.4% of widowed individuals were lonely and so were 47.6% of the divorced. 44.1% of people from low income household were lonely. So were 37.3% of economically inactive individuals and 21.7% of the self-employed. All variables were significantly associated with loneliness (p <0.001).

Marital status was a significant risk factor for loneliness (Table 3). Widowed and single people were more than two times as likely to feel lonely as the married (OR=2.60 for the widowed; OR=2.43 for the single; p < 0.001). Divorce/separation increased the odds of feeling lonely even more (OR=4.02; 95% CI, 3.20-5.04; p <0.001). The results of subgroup analyses indicate that ORs for all non-married statuses were greater in men than in women (Table 4). In particular, divorced/separated men were 5.24 time more likely to feel lonely, whereas divorced/separated women were 3.05 times more likely to feel lonely than their married counterparts (p <0.001).

In addition to marital status, age was shown to influence the risk of loneliness. The risk of loneliness was greatest for individuals aged 80 years and older (OR=1.81; 95% CI, 1.21-2.69, p <0.01). However, the increased risk of loneliness for old groups was significant only among men, according to the results of subgroup analyses by gender (OR=2.11; 95% CI, 1.11-4.03, p <0.05 for men aged 80 years and older). People from low income households were more likely to feel lonely as those from general households (OR=1.72; 95% CI, 1.44-2.04, p <0.001). So were economically inactive people than salaried people (OR=1.60; 95% CI, 1.33-1.92, p <0.001). Based on the Akaike information criterion (AIC) and -2 Log L measures, the model selected fit data for males better than for females (Table 4).

This study showed that loneliness is a highly prevalent problem in Korea. Based on nationwide survey data, approximately 20% of Koreans aged 30 year and older were estimated to feel lonely at least one day a week as if they were alone in the world. The prevalence of loneliness is higher than previously observed at 4.1% based on data from three cities in Korea [19]. Moreover, the prevalence estimated in this present study are, in general, higher than in other developed countries [13]. Specifically, the prevalence of loneliness measured using a single-item question varied widely across European countries; it ranged from 2.7% to 9.6% for mid-dle-aged adults (30-59 years) and from 5.2% to 21.3% for older adults (≥60 years) [13]. The prevalence of loneliness using a 3-item scale was 19.3% in community-dwelling U.S. adults aged 65 years and older [22]. However, the prevalence (20.2%) observed in this current study was low-er than that in the United Kingdom where 35.9% of residents sometimes or often felt lonely, according to a study based on data collected during the initial phase of the COVID-19 pandemic in early 2020 [16].

Overall, the high prevalence of loneliness calls for actions to identify risk factors. This current study showed that marital status was significantly associated with risk of loneliness in Korean adults aged 30 years and older. Compared to the currently married, all other non-married statuses increased the odds of feeling lonely. Consistent with the finding of this study, stable marriage appears to play a protective role in loneliness, according to a study based on data from 30 countries [23] as well as a study in Dutch adults [31]. The findings of the current and previous studied suggest that loneliness may be attributable to a change from being married to non-married state. However, there appears to be a differ-ence in the risk of loneliness among non-married statuses. The cause of transitioning to non-married state seems to play a role in loneliness. In this current study, divorced and separated people were at greatest risk of feeling lonely among all marital statuses. Similarly, in U.S. adults aged 65 years and older, being married with a spouse that is nonetheless absent increased the risk of loneliness than being widowed [22].

The role of gender in the risk of loneliness is unclear, because there are mixed reports on the relationship between gender and loneliness [19,22,29]. After adjusting for other covariates, gender was not associated with increased risk of being lonely in this present study. However, gender seems to have a differential effect on the relationship between other sociodemographic variables and loneliness. For example, in the subgroup analysis, the relationship between age and risk of loneliness was significant only in men. More importantly, compared to the currently married status, divorce/separation increased the risk of loneliness more in men than in women, while all non-married statuses (divorce/separation, widow-hood, and singlehood) were stronger predictors of loneliness in men than in women. The gender differences concur with the existing evidence [32,33]. Among older Koreans, not being married was positively associated with loneliness in men but not in women [33]. Similarly, loneliness is more strongly influenced by partner status among Dutch men than among women [34]. Pathway to dissolution of marriage appears to have a differential influence in loneliness between men and women [32]; among U.S. men, divorce was a stronger predictor of loneliness than death of a spouse, perhaps due to deteriorations in relations between divorced father and child.

In addition to marital status, age was identified as a risk factor for loneliness in the analysis of both men and women. People in the oldest age category of 80 years and older had an increased risk of loneliness compared to those in their 30s. Loneliness in older adults is likely to result from deteriorations in physical functioning and poorer health [22] and social life changes after retirement [15]. However, the association between old age and increased loneliness observed in this present is not universal [35,36]. Contrary to the current finding, old age was associated with decreased risk of loneliness in the United States [35] and in the United Kingdom during the COVID-19 pandemic [16]. Loneliness had a U-shaped association with age in the United Kingdom such that the levels of loneliness were highest in people under 25 years and over 65 years [36].

Compared to no or primary education, middle or higher education levels were associated with increased risk of feeling lonely. This is in part because learning is a lonesome endeavor in many instances. However, the role of education in loneliness is not straightforward, because schools provide an opportunity to socialize with other people and a means to make financial resources later in life [21]. Financial situation indeed seems to play a role in loneliness. In this current study, economically inactive people were more likely to be lonely than people earning salaries, which was consistent with the findings in the United Kingdome [16]. This oc-curs because unemployment means a lack of the setting and financial resources with which to socialize with other people. In addition to employment status, the financial situation of the household appears to be associated with loneliness. In this present study, people from low income households had a greater likelihood of feeling lonely than people from general households. These findings suggest that we as a society should pay a close attention to the economic needs of the vulnerable populations and that social support measures to address the loneliness epidemic may enhance the mental and emotional health of the economically disadvan-taged people.

To summarize, this study showed that loneliness is a highly prevalent problem in Korean adults and it is strongly associated with marital status, based on nationwide survey data. Given the paucity of research on loneliness in Korea, this study fills the gap in the domain knowledge. The findings will inform public health policies and social support measures that focus on subjective feelings of loneliness in the vulnerable populations. Despite the values added, the finding of this study should be inter-preted with caution in light of the following limitations. First, this study used a cross-sectional design, which may preclude causality inference from being drawn between marital status and loneliness. Second, data were self-reported. The prevalence of loneliness may have been underre-ported due to stigma attached as some researchers have suggested [22]. Third, this study did not account for the severity of loneliness by catego-rizing individuals into either the lonely or the not-lonely groups. Future research should consider not just the existence of loneliness but also the degree of loneliness as an outcome variable. Fourth, this study is based on a single-item measure of loneliness, which may have less sensitivity than multiple-item measures. Nonetheless, a single-item measure has been used in loneliness research [13]. Future research should consider using multiple item measures of loneliness. Lastly, this study examined only sociodemographic variables as potential risk factors for loneliness. However, the literature indicates that subjective health status, supportive family relationship, and functional limitations play a role in the risk of feeling lonely [37], which should be examined in the future study.

In conclusion, using nationwide survey data, this study showed that loneliness is a highly prevalent public health problem in Korean adults aged 30 years and older, and that marital status was strongly associated with increased risk for loneliness, after adjusting for other sociodemographic variables. The pathway to dissolution of marriage matters to the risk of loneliness. The odds of loneliness increased more for divorced/separated individuals than for widowed ones. Men were more susceptible than women to loneliness by transitioning from married to non-married status. The findings will help identify vulnerable populations who are in most need of social and psychological support and thus would be appro-priate targets for preventive intervention measures.