The Association Between Mental Health, Chronic Disease, and Retired Status Among Korean Elderly: A Cross-Sectional Study


 Background Retired status has strong associations with mental health factors and involves gender disparities. However, while retirement is known to affect the mental health of the elderly, large-scale studies examining the impact on mental health by gender are scarce.Methods This cross-sectional study examined the data of 1,664 participants aged over 65 years old who completed the economic status and mental health sections of the 6-7th Korean National Health and Nutrition Examination Surveys (2013–2017). We adjusted for covariates (health behavior, sociodemographic factors) in regression analysis for complex sampling design to calculate regression coefficients and 95% confidence intervals of the link between retired status and mental health. We also assessed which covariates of chronic disease, health behavior, and sociodemographic factors weakened the correlation between retired status and mental health.Results Retired status in Korean populations has persisted to negatively impact the incidence of depressive symptoms and thoughts of suicide, even after adjusting for confounding variables. Regarding mental health, women were affected by retired status to a greater extent than men. Among covariates, health behaviors and sociodemographic factors were most affected by retired status. Women were more affected by household income, and men were more affected by drinking behaviors.Conclusions These results imply that chronic diseases and psychological factors should be managed delicately among the retired elderly, and that there may be gender differences in retirement adaptation.

provide answers regarding their status of economic activity, and 113 respondents who were classi ed as unemployed for reasons other than retirement. Ultimately, responses from 1,664 respondents were analyzed. After modifying for propensity score matching (PSM), data from 475 employed people and 95 retired people were utilized in the analysis (Fig. 1.)

De nitions Of Retired Status
We de ned retired status among the respondents of KNHANES VI-VII as being aged older than 65 years and being unemployed due to age of retirement/retired status.

Mental Health
Perception of stress was classi ed into three categories: high (as indicated by a response of "very high" or "high"), low (as indicated by a response of "low") and almost none (as indicated by a response of "under almost no stress"). Psychiatric diagnosis of depression and experience of suicidal ideation were recorded by responses of "yes" or "no"; answer selections were based on whether the respondent had received a psychiatric diagnosis of depression and whether they had considered suicide, respectively.

Chronic Disease
The presence of chronic diseases including hypertension, hyperlipidemia, osteoarthritis, rheumatoid arthritis, diabetes, osteoporosis, pulmonary tuberculosis, and asthma was noted; respondents answered "yes" if they had been diagnosed by a physician and "no" if they had not.
Covariates Demographic characteristics such as gender and socioeconomic, lifestyle-related, and health-related characteristics were evaluated as covariates (age, sex, place of residence, education, marital status, household income, BMI, smoking, drinking, level of physical activity, and subjective perceived health). Sex was classi ed as "male" and "female," and age was treated as a continuous variable. Place of residence was categorized into "rural areas" and "urban areas." Education was classi ed into three categories of "elementary school graduate," "middle school graduate," and "high school graduate or higher." Marital status was categorized into "residing with spouse" and "not residing with spouse." Household income level was subject to equalization (dividing the monthly average household income by the number of members in a household), and then divided into two categories based on monthly average household income. BMI (kg/m2) was classi ed according to the World Health Organization's criteria and then reclassi ed into three categories: "underweight," "normal weight," and "overweight or obese." Smoking status was divided into "non-smoker," "ex-smoker," and "current smoker." Drinking habits were divided into four levels: (a) Nondrinkers, de ned as not having consumed alcohol in the past year; (b) Drinking once or less per month; (c) Drinking twice or more per month but less than 3 times a week; and (d) drinking more than four times a week. Regular walking was divided into "yes" or "no," depending on whether the respondent had walked more than 10 minutes for at least one day in the past week. Subjective health was classi ed into four categories: "very good" (as indicated by responses of "very good"), "good" (as indicated by responses of "good"), "moderate" (as indicated by responses of "moderate"), "poor" (as indicated by responses of "poor"), and "fair" (as indicated by any other responses).

Statistical analysis
KNHANES is a national study that applies both strati ed cluster sampling and weighted values. Among various analysis methods of complex sampling designs, this study used strati cation, clustering, and weighted variables for complex sampling design factors to analyze the data. All analyses were conducted using SAS version.9.4. (SAS Institute, Cary, North Carolina, USA), and were considered to be statistically signi cant if p < 0.05. Means and standard deviations are reported for continuous variables, and means and percentages (%) are reported for categorical variables. This study also utilized PSM to reduce the baseline differences of comorbidities. Thereafter, PSM was conducted using nearest neighbor matching without replacements for 1:5 matching. We used research. IRB approval was not required for the present study because it did not involve any sensitive information and accessed only publicly available data from KNHANES (JASENG IRB File No. 2020-03-002).

Results
Participant Characteristics Re ecting Retired Status (before/after Propensity Matching) Table 1 summarizes the clinical characteristics of the sample based on PSM. According to standardized bias (%), the clinical characteristics of the retired and non-retired groups were biased prior to PSM. Although we were not able to calibrate for minor differences, these biases were reduced signi cantly after 1:5 PSM. After PSM, a total of 570 participants were categorized according to sex (Table 2). Among men (n = 351), the majority of characteristics including the covariates of mental health did not differ signi cantly, aside from residence (p = 0.0171) between groups. Among women (n = 219), there were signi cant differences only in the household income level (p = 0.0097); however, the general patterns of characteristics were similar to those among men (Table 2). Table 1 Characteristics of Korean elderly ≥ 65 years participating in KNHANES VI -VII (2013-2017), before and after PSMa.

Variable
Before propensity score matching After propensity score matching b Retired status applies to individuals who were not working as they had reached the age of retirement and had already retired.
c Employed status applies to individuals who were working at least one hour per week for the purpose of income, or working 18 hours or more in a nonpaid family environment.
d Partnered refers to individuals who were residing with their spouses. e Household income level was calculated by dividing the total household monthly income by the obtained levels and grouping the results into quartiles.
f Regular walking refers to having walked for more than 10 minutes a day for at least one day a week. e Regular walking refers to having walked for more than 10 minutes a day for at least one day a week.

Relationship Between Retired Status And Mental Health
Overall, stress perception was low in the retired group, with men and women demonstrating similar trends in this regard. On the other hand, differences were observed for the incidence of depressive symptoms and the presence of suicidal ideation. Regarding the incidence of depressive symptoms, retired status was more in uential for women than for men. We were not able to analyze the presence of suicidal ideation among men due to a lack of data; among women, the odds ratio (OR) was 6.39 (95% CI 0.64-64.48) in Model 2, which was adjusted for age and other variables. This indicates that after adjustment for other variables such as age, smoking, drinking, education level, household income, and physical activity, retired status signi cantly exerted a negative in uence on the presence of suicidal ideation among women (Table 3).   In uence of covariates in the linear regression analysis on the correlation with retired status and mental health of elderly participants We evaluated the in uence of each covariate block (somatic health, health related behavior, and sociodemographic factors) on the correlation between retired status and mental health after adjusting for age and sex (Table 5). The non-standardized regression coe cient relating to mental health among elderly men was − 0.234, which increased slightly after adjusting for age and sex; the non-standardized regression coe cient relating to mental health among elderly women decreased slightly to -0.309 after adjusting for age and sex. The negative values present for both men and women indicate that overall, retired status negatively in uenced participants' mental health. Non-standardized regression coe cients were used as a standard of comparison with other variables. Therefore, adjusting for somatic health, health behavior, and sociodemographic factors, the absolute value of the difference between the two coe cients re ected the differences in effect size of each factor.
Among men, the absolute difference between − 0.207 and the regression coe cients of each factor re ected the individual impact; the factor with the most signi cant in uence was health-related behavior, which reduced the connection with mental health by 3%. The variable with the most signi cant weakening in uence among health-related behaviors was alcohol consumption (1.9%). Sociodemographic factors weakened the association with mental health by 1.5%; two notable individual factors were living with one's spouse and type of residence, with 3.4% in relevance. Among the physical health variables, only osteoarthritis and rheumatoid arthritis showed a weakening in uence (3.5%); the rest of the chronic disease variables did not have much impact.
Using the same mechanism, we also explored factors that reduced the association with mental health among women; in terms of large categories, sociodemographic factors reduced the impact by 2.5%, and the physical health and health-related behavior factors did not have much impact. However, we noted some differences in results when assessing the impact of individual factors. Osteoporosis, one of the sub-items within the physical health variable, indicated a relatively large impact size of 4.2%. Among sociodemographic factors, household income level had a signi cant impact of a 22.8% reduction, whereas other factors were not very impactful.
When comparing results after adjusting for all variables, the association between retired status and mental health among the elderly decreased by 1% among men and increased by 28% among women. These results indicate that the mental health of men is more heavily impacted by retired status than the mental health of women.

Discussion
The mental health-related variables that were explored among the elderly in this study were divided into stress perception, psychiatric diagnosis of depression, and presence of suicidal ideation. Interestingly, they demonstrated different trends in being in uenced by retired status. The observation that there were lower levels of stress perception among both men and women after retirement can be interpreted as the participants having previously been in stressful occupational and/or social environments that they no longer experienced. Furthermore, despite the lack of data as a limitation, retired status generally had a negative in uence on the incidence of depressive symptoms and the presence of suicidal ideation.
The results of this study were not too far removed from those of the majority of previous studies with similar objectives. One such study found retirement to have a negative in uence on mental health and morale [8], and another study reported that suicide rates were higher after retirement [9].
A major factor that impairs the mental health of the elderly post-retirement is retirement stress, which can be explained using the social stress model [10].
According to the model, retirement stress includes the feeling of loss due to reduced income, changes to daily life, deterioration of status both at home and in society, loss of self-identity, changes to one's social network, reduction of meaningful life experiences, and negative attitudes towards retirement [11].
Depression is one of the most common mental health symptoms that the elderly experience due to maladaptation to retirement stress. A study that analyzed the relationship between retirement and depression among the retired elderly found that retirement led to declines in mental health and expected that lower retirement satisfaction could lead to depressive symptoms [12]. Furthermore, another study reported that retired individuals experienced higher incidence rates of various mental illnesses, including depression, compared to those who are employed [13].
We found that changes to the physical and psychological environment due to retirement in uence mental health and in uence the occurrence of chronic diseases. Behncke et al. [14] utilized data from the English Longitudinal Study of Ageing to analyze the various effects of retirement on health results using non-parametric matching and tool variables (IV), concluding that retirement increases the risk of chronic condition diagnosis by 10%. Particularly, they reported that retirement raises the risks of cardiovascular disease (4%) and cancer (3-4%) diagnoses, and that it was likely to cause issues in physical activity.
Furthermore, a study by Alvinia found that leaving the labor market has a negative in uence on chronic disease occurrence in many European countries [15].
In addition to yielding cross-sectional results, this study aimed to discover the most in uential factors among multiple covariates that were impactful on the in uence of retired status on elderly mental health. Among numerous results that can be found in Table 5, some notable points included that alcohol consumption was the most in uential covariate among men, and that the sociodemographic block was the most in uential among women.
Drinking in old age can lead to various geriatric physical conditions, and often causes psychiatric issues [16]. Experiencing a loss of social roles, reduced economic power, loneliness and alienation, and deaths of spouses after retirement leads to the experience of feelings such as helplessness, isolation, and selfblame; this may lead to new tendencies to drink or binge drink, or exacerbate existing problematic drinking [17]. Particularly, middle-aged men in Korean society may experience excessive stress and maladaptation to their post-retirement lives and are likely to engage in problematic drinking [18].
On the other hand, it is important to compare the retirement environment that women face when discussing the issue of retirement for elderly Korean women.
Female Korean retirees comprise a generation that had to construct their own career paths while facing a lack of understanding regarding women's employment due to the residue of patriarchal values; as such, they maintained their occupational status amidst social expectations and norms that differed from those for men, who were praised as work-oriented tendencies were equated with the responsibilities of the breadwinner [19]. Considering the particular cultural environment that Korean employed women faced, we are able to infer that the in uence of sociodemographic factors will be signi cant.
There are two major points of views on elderly retirement. One point of view is viewing retirement as a crisis. In other words, retirement is regarded as a signi cant crisis faced during the later half of one's life, resulting in a loss of status, a loss of self-identity, non-productive leisure time, and the social stigma of incompetence. On the other hand, the other point of view considers retirement to be a continuous phase of the life cycle. This viewpoint regards retirement as a predictable process, rather than a crisis that one abruptly faces. Furthermore, this viewpoint does not equate work with life, but instead regards it as a temporary task at a speci c stage of life, asserting that retirement is not as signi cant a crisis as is commonly believed. Reviewing these two contrasting viewpoints in relation to the cultural characteristics of Korean society and mental health of the elderly, we are able to conclude that in Korea, retirement is likely to be perceived as a stressful event for the individual instead of as a simple change in environment. This is due to factors such as a comparatively younger retirement age, a lack of preparation for retirement, involuntary retirement, and weak social safety nets; furthermore, it can also be predicted that postretirement adaptation will be relatively di cult [20].
However, not everyone who retires experiences declines in mental health. Jokela et al. [21] asserts that retirement has a positive in uence on mental health, and that legal retirement and early voluntary retirement improve health status and physical functions. In a similar context, Charles et al. [22] found that freedom from labor via retirement has a positive in uence on life satisfaction.
These differences can be attributed to individual vulnerabilities; although the retirees experience stress from retirement, an environmental event, the possibility of experiencing deteriorated mental health changes depending on the individual's level of vulnerability. This can be explained using the stress-vulnerability model. The stress-vulnerability model is useful in understanding the causes and processes inducing mental illnesses through the interaction between individual vulnerability and environmental stress [23], and existing studies [24,25] have attempted to approach elderly mental health issues through this model.
The main advantages of the present study are as follows. First, the health-related survey used in this study was conducted by trained professionals using a national sample of Koreans in a systematic manner. This study is valuable as it is the rst study to comprehensively evaluate the effect of retirement on the mental health status of elderly Koreans on a national level. Another advantage is that we went beyond exploring cross-sectional association by adjusting factors that could act as confounding variables in the association between retired status and mental health variables to explore the level of in uence of such factors on retirement and mental health levels.
However, this study also has the following limitations. First, given the cross-sectional study design, which limits the study to a short and speci c period of time, this study can only derive associations rather than causal relationships.
Another limitation of this study is that the response data re ecting the mental health status of the elderly, such as levels of perceived stress and presence of suicidal ideation, were self-reported. This is a limitation because self-report surveys can lead to subjective and biased results, which differ from physicians' diagnoses or diagnostic testing results. Furthermore, these self-report surveys carry the risk of being exposed to memory bias.
Lastly, a clear limitation of this study is the failure to obtain su cient data for certain factors, which may have led to these factor acting as confounding variables in the regression analysis despite the fact that this study was carried out based on the results of a national survey. First, when analyzing healthrelated behaviors, we were not able to re ect the elderly female smoker population as there were no smokers among the studied female retirees. Furthermore, when examining the presence of suicidal ideation as one of the mental health variables, we were not able to examine this factor among men due to a small sample size. Although we were able to obtain an OR value of 3.2 across both genders, it would be di cult to compare gender-speci c differences for this factor.

Conclusions
Ultimately, the experience of retirement in old age is negatively associated with the mental health of the elderly and health-related behaviors such as drinking and sociodemographic factors strengthen this negative relationship. These results were more pronounced among women, perhaps due to the characteristics of Korean culture that re ect different job perceptions and gender roles for women and men. Follow-up studies should identify the mechanisms underlying declines in mental health over time during retirement and explore protective factors that can mediate the association between the continuation of retirement and the deterioration of mental health.
Abbreviations CI, con dence interval; KCDC, Korea Center for Disease Control and Prevention; KNHANES, Korean National Health and Nutrition Examination Surveys; OR, odds ratio; PSM, propensity score matching; DM, diabetes mellitus; RA, rheumatoid arthritis.

Declarations
Ethics approval and consent to participate IRB approval was not required for the present study because it did not involve any sensitive information and accessed only publicly available data from KNHANES (JASENG IRB File No. 2020-03-002).

Consent for publication
Not applicable.

Availability of data and materials
The datasets generated and analysed during the current study are available in KNHANES repository (http://knhanes.cdc.go.kr). All data from KNHANES VI-VII are coded and freely available.
Competing interests TYK analysed and interpreted the data and drafted the manuscript. SHL acquired, analysed and interpreted the data. IHH acquired the data and made substantial contributions to the conception and design of the study. EJK, JHK, and SYC revised the draft manuscript. All authors read and approved the nal manuscript.