Suicidal ideation can directly link to actualizing an attempt. Therefore, it is a key concept for suicide prevention [1]. South Korea has the highest number of suicide attempts among Organization for Economic Co-operation and Development (OECD) countries [2]. Suicide, alongside with cancer and cardiovascular diseases, is a leading cause of death in Korea. It is the first-leading cause of death for teens and people in their 20s, second for adults in their 40s and 50s, and fourth for the elderly [3]. Each year, approximately 5,000 elderly citizens commit suicide in Korea, and about 4% of suicide attempts cause fatality [4]. Furthermore, there is a much higher rate of suicide attempts, and an even higher rate of suicidal ideation [5]. Suicidal impulse leads to ideation, which can trigger an attempt and cause fatal damage. Therefore, intervening when one conceptualizes suicide and/or feels an impulse is critical for prevention [6].

Individuals experience different life events and environments, and triggers for suicidal ideation vary depending on individual experiences. Humans have different developmental tasks that need to be solved through the lifespan, and negative life experiences often manifest differently across age groups. Traumatic experiences during one’s childhood and youth can lead to emotional instability and mental maladjustment, which are correlated with suicide attempts. In adolescence, problems such as poor academic performance, drinking, stress from school or family problems, lack of emotional support, urge to run away, and depression tend to be a problem [7]. In the 20s, lack of impulse control, uncertainty of future, academics, financial, and relationship problems are common problems [8,9]. For elderly citizens, financial instability, illness, chronic pain, health status, and relationship issues may be critical [10,11]. Likewise, young people under 40 and middle-aged people over 40 have different developmental tasks. Accordingly, life stressors and factors influencing suicidal ideation will differ. Young adulthood is a period when one becomes a legal adult and starts to live independently, become involved in an active social life, and must adapt to social demands and physiological changes. Mid- to late-adulthood requires continued career development, caring for one’s own family and parents, and preparing for retirement. With aging, elderly individuals need to prepare for changes in physicality and adjust accordingly [12].

Many studies have investigated suicide in recent decades; however, studies on adults examining the factors related to comparative rituals and social perspectives have been lacking. Some studies have reported that education, job, divorce [13], family conflict, financial problems, social relationships, unemployment [14], depression, despair, stress level, family cohesion [15], stress, gender, education, marital status [16] have been associated with suicide in adults. Considering the recent trend of increased adult suicide [3], investigating suicidal thoughts experienced by adults is essential. In reality, suicide is socially, culturally, and ethically prejudiced, so access is limited. Moreover, it is difficult to investigate because individuals are reluctant to expose their own or their family’s experiences with suicide. Most previous studies have been cross-sectional, making it difficult to address causal relationships between each factor at a given time [17]. Thus, this study performed secondary data analysis using the Korea Health Panel (KHP) data, which are collected nationwide from the same people annually. Suicide may be impulsive, but in many cases, it is the result of an accumulation of various psychosocial issues. From that perspective, this study investigated the accumulated effects of physical and perceived psychological states of an individual on suicidal ideation 1 year later.

The objective of this study was to determine the prevalence of suicidal ideation among young (19–39 years) and middle-aged adults (40–64 years), and to explore the risk factors for suicidal ideation.

Suicide is a reflection of individual’s internal psychological state, and so it should be understood in relation to one’s personal and social context [19]. In particular, different from existing research, this study used data from 2012 for its independent variables and 2013 data for the dependent variable, making it a 1-year longitudinal study. The results suggest that somatic and social psychological states as well as situational factors influenced suicidal ideation after 1 year. The results suggest that these factors act in the longer term rather than only in the urgent moment of suicidal ideation. This may magnify the importance of the potential risk factors identified here.

In analyzing the prevalence of suicidal ideation, 5.0% of all subjects—4.4% of young adults under 39 years and 5.6% of middle-aged adults between 40 and 64 years—reported experiencing suicidal ideation. A study using national survey data reported a 4.1% rate of suicidal ideation among adults aged 19 to 65 years [20]. In another study analyzing the National Health and Nutrition Survey, suicidal thoughts among adults over 20 years were reported in 15.3% of the sample [21]. This difference may be attributable to differences in the time of data collection and sampling method.

In the multivariate logistic regression analysis, Model I for young adults showed higher suicidal ideation among those who had less education and lower income. Less education likely leads to fewer employment opportunities, low economic power, and low health status [22], thereby leading to increased suicidal ideation. For young adults, people who have lower income experience suicidal ideation at least twice as much as those with a higher income. In Japan, where the distribution of suicides has increased sharply in men aged 35–64 years, 32% cite economic reasons, 16% of whom are reported to have a large amount of debt [23].

In Model II for young adults, heavy drinkers were 1.62 times more likely to experience suicidal ideation than non-heavy drinkers. In the case of heavy drinking, suicide can be attempted impulsively due to a decrease in the capacity for rational judgment [24]. Frequent heavy drinking can act as a mediator of negative emotions such as depression, which can further strengthen suicidal ideation [25]. Frequent heavy drinking can develop into problem drinking, such as alcoholism, which can affect suicidal thoughts [26]. Accordingly, health professionals should pay close attention to these young adults.

In a previous study on the relationship between drinking and suicide in adults, problem drinking and alcohol addiction increased depression and affected suicide attempts [27]. As more than 90% of suicides involve psychological problems such as alcohol dependence [14], counseling and intervention should be provided to help solve drinking problems. In Model III for young adults, social class perceptions did not reach significance, despite showing statistically significant differences in the chi-square analysis. Income level and heavy drinking were identified as the main risk factors for suicidal ideation in young adults.

In Model I for middle-aged adults, the prevalence of suicidal ideation showed significant differences by education and income level, just as in young adulthood. In Model II, there was a significant difference by subjective health status. In previous studies, subjective health status has been reported as a major risk factor for suicidal ideation across all adult age groups [28,29]. Subjective health status influences various domains such as physical and mental function, activities of daily living, and quality of life [30,31]. Therefore, if subjective health status is negative, it affects an individual negatively, and consequently, can trigger suicidal ideation. Subjective health status may be a judgment of one’s actual health status or may differ from one’s actual health status. Dissatisfaction with one’s physical condition can sometimes lead to problems in social interaction and affect suicidal ideation [32].

In Model II for middle-aged adults, subjective peer-compared health status was a major risk factor, contrary to the finding in young adults. Perceived peer-compared health status again may be subjective or reflect one’s actual health status. However, people who feel that their health is worse than that of their peers can become depressed and show decreases in activities of daily living and social activities [33]. Accordingly, negative perception of one’s own health may relate to suicidal ideation. This result supports the findings of previous studies showing a close relationship between subjective health status and suicidal ideation [34,35].

When looking at Model III for middle-aged adults, educational status, income status, and subjective health status showed statistical significance. Additionally, the query “Our society is given the opportunity to succeed if one makes efforts” was a factor, as those who responded negative to this query were 1.59 times more likely to experience suicidal ideation. Only 49.6% and 51.9% of young and middle-aged adults, respectively, responded “yes” to this query. There are many implications for suicidal ideations related to negative feelings about a chance to succeed. Such negative perspectives have profound ties to suicidal ideation, especially for middle-aged adults. In responding “no” to the query, middle-aged adults endorse the idea that no matter how hard one tries, one may not be granted opportunities, and that the future may not hold anything different from the present. Thus, one may conclude that life cannot with any certainty be changed for the better [36]. Deprivation of opportunities in this age group can lead to despair, and such negative thoughts can trigger suicidal ideation.

A common factor triggering suicidal ideation in both young and middle-aged adults is income. In another study, suicidal ideation was high in low-income families [28] and those with high family support burden. Debt holdings have also been found as a risk factor [37]. In particular, low total household income and debt are indicators of suicide risk among those who struggle to clear long-term debt or adults with urgent financial predicaments [37,38]. Korean middle-aged adults went through financial turmoil during the national financial crisis era, experiencing unemployment and seeing suicide rates spike [38]. The aftermath of the era, which included reduced employment opportunities and low incomes, may remain. In addition, middle-aged and low-income men who have traditionally been responsible for the household may feel the urge to commit suicide because of financial burdens [5].

Suicidal ideation is caused by a combination of factors. Thus, it is necessary to identify risk factors in each generation and adopt a multifaceted approach to prevent suicide. The conclusions based on the present results are as follows. First, a considerable number of young and middle-aged adults experience suicidal ideation, which should increase awareness of the risk of suicide in adulthood as well as other risk groups, such as the elderly. Second, education and employment opportunities should be expanded for less educated and low-income adults. Third, for heavy-drinking adults, close attention needs to be paid to avoid negative emotions such as self-pessimism or depression. Fourth, positive perceptions of health status must be reinforced to avoid a sense of inferiority compared to one’s peers. Fifth, negative perceptions of ‘not being given the opportunity to succeed even with much effort’ are likely to lead to frustration and suicidal ideation among middle-aged adults, and so it is necessary to improve the employment system by stimulating job creation or reemployment for the unemployed or early retirees.

One limitation of this study is that the analyzed data were secondary. However, the data are managed in a reliable manner by the KHP. Further, data were collected by face-to-face interviews, thereby limiting the effects of exposure on disclosing suicidal ideation. In addition, because the answer to the question about the suicidal ideation was either “yes” or “no,” the seriousness of suicidal ideation is not known. Accordingly, it is necessary to study suicidal ideation through in-depth interviews.