Association between exercise variations and depressive symptoms among precarious employees in south korea

ABSTRACT Research regarding the association between depression and exercise has been limited regarding precariously employed individuals. The current study investigated the association

between exercise variations and depressive symptoms among precarious employees in South Korea. Data from the 2014, 2016, and 2018 Korea National Health and Nutrition Examination Survey

(KNHANES) were analyzed. In total, 13,080 participants aged ≥ 19 years responded to the survey. The Korean version of the PHQ-9 was utilized in addition to questions assessing regular

exercise. Precariously employed men engaging in two or more variations of exercise each week were significantly less likely to report depressive symptoms (adjusted (OR): 0.78; 95% CI

0.62–0.97; p = 0.025), and the likelihood of depression was also lower for women who engaged in one or more forms of exercise (adjusted OR: 0.82; 95% CI 0.71–0.94; p = 0.006). These findings

support the association between depression and exercise and suggest that greater variations in regular exercise are associated with a reduction in depression for men whereas any form of

exercise reduces the risk of depression in women. SIMILAR CONTENT BEING VIEWED BY OTHERS SEX DIFFERENCES IN TYPE OF EXERCISE ASSOCIATED WITH DEPRESSION IN SOUTH KOREAN ADULTS Article Open

access 26 October 2020 THE PREDICTORS OF HEALTH-ENHANCING PHYSICAL ACTIVITY AMONG WORKING WOMEN IN SINGAPORE TWO YEARS INTO COVID-19: A CROSS-SECTIONAL STUDY Article Open access 13 December

2022 BIDIRECTIONAL RELATIONSHIPS BETWEEN PHYSICAL EXERCISE AND DEPRESSIVE SYMPTOMS AMONG CHINESE OLDER ADULTS EVIDENCE FROM THE CHINA FAMILY PANEL STUDIES Article Open access 05 May 2025

INTRODUCTION Employment stability has been a significant contributing factor in socioeconomic status, which directly influences one’s health status1. Precarious employment is considered as a

determinant of health, as it not only influences the health and well-being of employees but also their families and associated communities2. The negative effects of precarious employment

have been associated with a higher prevalence of mental health conditions including depression and anxiety3, 4, in addition to reduced health-related quality of life5. Such mental health

consequences have become one of the greatest health problems leading to the global socioeconomic burden6, 7. Depression may affect a person’s well-being in addition to impairing daily and

professional functioning8. Furthermore, depression can not only directly result in considerable costs including healthcare services, but it can also have an indirect and substantial impact

resulting in reduced productivity, work capacity, and even early retirement9, 10. Studies on depression among employees have shown that depression is a major cause of long-term sickness

absence11. Thus, studies have highlighted the importance of health promotion including counseling services, stress management, and improvement in work environment settings to prevent

depression among employees, although these have only displayed minor effects12. Furthermore, work-directed interventions including work adjustments and additional coaching provision have

also demonstrated promising outcomes13. Reduced physical activity is determined to be one of the main features of depression and is included in the diagnostic criteria of depression14.

Previous research has suggested that exercise may play a role in the reduction of depression15; thus, numerous studies have focused on physical activity interventions to reduce depressive

symptoms, at least within the clinical population16, 17. Supervised strength training have also demonstrated positive effects on depression in comparison to relaxation18, whereas aerobic

exercise did not demonstrate any effects19. Likewise, recent research suggests that anaerobic exercise also helps to reduce depressive symptoms20. Nonetheless, longitudinal studies have

failed to identify the consistent effects of physical exercise on the psychological symptoms of the general population17. Moreover, whilst studies have assessed workplace exercise

interventions to reduce the risk of depression among sedentary employees and improve work-related outcomes such as the increase in work attendance and reduction of job stress21, these were

mostly focused on permanent employees, without the consideration of factors surrounding precarious employment8. As a result, many aspects of how physical exercise prevents depression remain

unclear22; with almost no studies to show the impacts of exercise among precarious employees. Beyond the existing bilateral relationship between exercise and depression, previous research

has demonstrated the efficacy of various exercise combinations in greatly improving physical health as compared to engaging in no exercise or only a single type of exercise23, 24. Therefore,

the following study will investigate whether a combination of different exercises will have subsequent effects on the levels of depressive symptoms among precariously employed individuals

in the South Korean population. In addition, sleep plays a vital role in maintaining homeostasis and also enhancing mental and physical well-being25. However, sleep disturbances are typical

among most depressed individuals with studies demonstrating a strong bilateral association between sleep and depression26. Additionally, many precarious employees are at risk of such sleep

disturbances due to their work hours and also insecurities27, 28. Henceforth, understanding the importance of sleep on one’s well-being, the association of sufficient sleep and depressive

symptoms will also be evaluated for the current study. RESULTS DESCRIPTIVE STATISTICS Among the participants, 12.0% of men and 19.7% of women scored 5 or above on the PHQ-9 scale for

depressive symptoms. Both men and women who engaged in more variations of exercise reported a reduced prevalence of depressive symptoms in comparison to those not engaging in regular

exercise. Among men, those who reported excessive amounts of sleep demonstrated the greatest prevalence of depressive symptoms in comparison to insufficient and normal levels of sleep (20.4%

vs. 12.0% vs. 11.1%, _p_ = 0.026). However, those with insufficient sleep had highest depressive symptom scores, followed by excessive and then normal levels (20.5% vs. 19.5% vs. 16.9%, _p_

 = 0.005) for female employees. Overall, both men and women with depressive symptoms reported lower levels of educational attainment, lower household income, current smokers, more likely to

be unmarried and be diagnosed with a metabolic syndrome. While there was no significant difference according to residential area among men, for women, those living in rural areas reported a

greater prevalence of depressive symptoms (21.6% vs. 19.3%, _p_ = 0.048). The details are provided in Table 1. GENDER DIFFERENCES IN THE ASSOCIATION BETWEEN EXERCISE AND DEPRESSIVE SYMPTOMS

Multivariable logistic regression was conducted to evaluate the association of depressive symptoms with exercise variations, as demonstrated in Table 2. Precariously employed men engaging in

two or more variations of exercise each week were 0.78 times less likely to report depressive symptoms (adjusted Odd Ratio (OR): 0.78; 95% CI 0.62–0.97; _p_ = 0.025), thus representing the

association between exercise and the reduction of depressive symptoms. However, women who engaged in even just one form of exercise reported a reduced likelihood of depression (adjusted OR:

0.82; 95% CI 0.71–0.94; _p_ = 0.006), as well as those engaged in two or more variations of exercise (adjusted OR: 0.72; 95% CI 0.62–0.83; _p_ < 0.001). Both men and women who were

current smokers, underweight or had metabolic syndromes had higher likelihood of reporting depressive symptoms. Notably, insufficient sleep was not a significant factor for men; however,

women who reported insufficient levels of sleep were 1.18 times more likely to have depressive symptoms (adjusted OR: 1.19; 95% CI 1.03–1.38; _p_ = 0.020). Regarding marital status, women

who were either separated, divorced, or widowed had significantly higher likelihood of reporting depressive symptoms whereas there was a higher possibility of depressive symptoms among men

who were never married or were either separated, divorced, or widowed. On the contrary, increased household income and higher educational attainment (high school for men and high school and

above for women) reported a reduced likelihood of depressive symptoms. COMBINED EFFECTS OF EXERCISE VARIATIONS AND COVARIATES ON DEPRESSIVE SYMPTOMS A subgroup analysis of the combined

effects of exercise variations and each of the covariates on participants’ depressive symptom levels was performed. Table 3 reports the levels of analysis among men and Table 4 reports the

outcomes among women. The association between sleep and exercise variations differed between each gender in terms of depressive symptoms. Only men having insufficient levels of sleep and

engaged in two or more variations of exercise reported they were 0.72 times more likely to experience depressive symptoms (adjusted OR: 0.72; 95% CI 0.57–0.91; _p_ = 0.005). Other sleep

durations and exercise did not have any association with depressive symptoms. However, both insufficient and excessive sleep was associated with likelihood of reduction in depressive

symptoms for women when engaged in any form of exercise. Those who engaged in a single variation of exercise per week and reported having insufficient levels of sleep had a 0.77 times

likelihood of reporting depressive symptoms (adjusted OR: 0.77; 95% CI 0.66–0.90; _p_ = 0.001) and a 0.30 times likelihood of depressive symptoms for those having excessive amounts of sleep

(adjusted OR: 0.30; 95% CI 0.11–0.86; _p_ = 0.025). Interestingly, there was even a greater reduction in the likelihood for women engaged in two or more variations of exercise. Women with

insufficient sleep reported a 0.65 times likelihood of reporting depressive symptoms (adjusted OR: 0.65; 95% CI 0.56–0.76; _p_ =  < 0.001), whilst those who with excessive amounts of

sleep had a likelihood of 0.19 for reporting depressive symptoms (adjusted OR: 0.19; 95% CI 0.06–0.59; _p_ = 0.004). This demonstrates the importance of exercise and reduction of depressive

symptoms regardless of the sleep levels of the individual, particularly for precariously employed women. The combined effects of low educational attainment, lower income, non-alcohol

drinker, non-smoker, living in urban areas, and exercise variations (both one and two or more variations) demonstrated a linear association with depressive symptoms among women. However, for

men, household income had no association whereas the association of reduced depressive symptoms and exercise was presented for those with greater than university degree attainment.

Regarding metabolic syndrome, the distinct gender effects have been identified. Men with metabolic syndromes did not demonstrate any effects of exercise on depression yet women who exercised

on two or more variations had a significant reduction in the likelihood of having depressive symptoms (adjusted OR: 0.47; 95% CI 0.33–0.67; _p_ = 0.001). Detailed subgroup analyses of male

participants are presented in Table 3 and analyses of female participants are demonstrated in Table 4, illustrating the gender effects in the association between exercise variations and

depressive symptoms. DISCUSSION Employment status and stability have been considered to be a significant indicator of one’s health and socioeconomic status1, where precarious employment is

associated with an insecure form of employment, lower-income, and poorer working conditions29. This potentially leads to a higher prevalence of mental health conditions and reduced quality

of life3,4,5, 30. Nonetheless, research on methods to support and promote the well-being of the precariously employed population have been limited. Henceforth the current research

specifically examined the levels of depression and effects of exercise among precariously employed individuals within the South Korean population to address these risks. The association

between combinations of weekly exercise and the onset of depressive symptoms within the precariously employed population in South Korea was explored using 2014, 2016 and 2018 editions of the

KNHANES. The current research aimed to identify associations between depressive symptoms and exercise variations including walking, strength exercise, and aerobic exercise. Both men and

women reported a reduction in depressive symptoms when undertaking variations of physical exercise each week. The current findings were consistent with existing studies on physical activity

being efficacious in reducing depressive symptoms15. In this study, there was a reduction in depressive symptoms among employees engaging in regular form physical activity. However, this

study was novel in its approach to investigate the association of weekly exercise combination on individuals’ depressive symptoms. Significant effects of exercise variations were detected

within precarious employees. Upon close subgroup analysis, precariously employed men reported a reduction in depressive symptoms when engaging in two or more different variations of exercise

whereas female employees who engaged in any single form of exercise or more per week displayed reduced depressive symptoms. Thus for men, exercise diversity and combination are vital, in

comparison to women whose depressive symptoms were reduced even though they engaged in only one form of exercise. In addition to regular exercise, reduction in sleep duration and quality

have often been reported due to the shift in employment conditions towards requiring greater hours of work as well as night activity28, 31. This has significantly affected employees’ sleep

patterns and increased fatigue, tiredness, and daytime sleepiness31. Existing research has established an association between sleep and depression, considering its complex and bidirectional

nature and placing great emphasis on sleep duration and also the quality of sleep32, 33. Thus, in addition to the effects of exercise variation, the current study also investigated the

impact of sleep on depressive symptoms as those in precarious employments are most at risk of lacking sleep and having poor sleep quality27. Upon conducting subgroup analyses, results showed

that sleep did not affect the level of depressive symptoms among men. However, women with insufficient sleep (less than 6 h per day) reported an increased likelihood of depressive symptoms.

This demonstrates the potential gender affect on the association between exercise and sleep of precarious employees, with women being more vulnerable to risks associated with insufficient

sleep. Additionally, while sleep did not have a direct association with depression among men, insufficient sleep coupled with two or more types of exercise was associated with rather reduced

depressive symptoms. In contrast, for women with insufficient sleep, the subgroup analysis showed a reduction in depressive symptoms when this was coupled with both one type of exercise and

two or more combinations, again demonstrating the importance of any form or combination of exercise in women. Furthermore, women engaging in two or more types of activity coupled with

excessive sleep (9 h and more per day) also demonstrated a reduction in depressive symptoms. This highlights the importance of participating in exercise combination whereby, taking part in

such exercise variations could potentially supplement the lack of sleep for men and women and reduce depressive symptoms. In line with existing studies, consistent trends of reduction in

depressive symptoms were associated with an increase in household income, whereas there was an increase in depressive symptoms among both men and women who were smokers, non-married

(including divorced, separated, and widowed individuals), and underweight1, 34, 35. This study also identified the effects of exercise among those with metabolic syndromes. Whilst exercise

was not an influential factor for men, women who participated in two or more diverse form of exercise activity had demonstrated a reduced likelihood of depressive symptoms. The current

study’s strengths include the following. Firstly, the study assessed the effects of exercise variation on the precariously employed population within the South Korean population. It was the

first of the kind to investigate the combined effects of exercise rather than observing the effects of individual exercise types. Furthermore, prior studies have examined the association of

depression and exercise among regular, permanent employees8 yet, specific attention to precarious employees have been absent in research. Consequently, this study has focused on the

precariously employed population who have a higher risk of having problems related to mental and physical well-being36, 37. Hence, the current research has identified the direction that

further research should take in order to support the well-being of these vulnerable employees. Moreover, the study used a nationwide population survey conducted over a 3 year period; thus, a

large population was recruited and the sample may be representative of the South Korean population and the findings may be generalized38. The study also has its limitations. Due to research

being observational and correlational, it is unable to identify whether exercise variations reduced the likelihood of depressive symptoms or those with lower depressive scores were more

likely to exercise. While it was imperative for this study, as the first original research, to identify this association, future research investigating causation among these variables should

be conducted within the context of employment in South Korea. Furthermore, as the current study only involved precarious employees, future research comparing the association between

exercise and depression for both precarious and permanent employees would provide additional information in managing the well-being of employees subject to their needs. Additionally,

considering the innovative nature of the current research, grouping the physical activity responses into a new variable of exercise may have its limitations in assessing the combinations of

exercise. More categories besides strength, aerobic, and walking exercises should be included to identify more specific features for the association between exercise and depression. Overall,

the current study demonstrated new and insightful findings regarding the relationships among exercise variations, sleep, and depressive symptoms in precarious employees. These associations

were also moderated by gender, and the study also identified potential methods to reduce depression among precariously employed individuals. Based on the findings, precariously employed men

may benefit in terms of mental well-being if they engage in various combinations of weekly physical exercises, whereas women can benefit from engaging in even just one type of exercise

regularly. Further research should be conducted to determine the causality of the association on a longitudinal scale as well as identify specific types of physical activity that can

significantly reduce the risks of depressive symptoms among precarious employees who may be at risk for depression. METHODS PARTICIPANTS Responses from the 6th and 7th Korea National Health

and Nutrition Examination Survey (KNHANES), conducted by the Korea Disease Control and Prevention Agency were assessed. The survey was conducted amongst the non-institutionalized South

Korean civilians throughout 192 regions to monitor the trends in health risk factors alongside the prevalence of major chronic disease and evaluate the health and nutritional status. In

total, 10,000 individuals aged ≥ 1 year are selected for the survey each year and divided into three groups according to the stages of life: children (aged 1–11 years), adolescents (aged

12–18 years), and adults (aged 19 years and over). The database is publicly available on the KNHANES website (http://knhanes.cdc.go.kr). The patient health questionnaire (PHQ-9) is

administered biannually; hence, the current study used data from the 2014, 2016 and 2018 KNHANES. A total of 23,692 individuals responded, those without a valid PHQ-9 score (_n_ = 7064),

those not in precarious employment (_n_ = 3033), without a valid exercise score (_n_ = 71), missing sleep score (_n_ = 54) and those missing covariate values (_n_ = 1033) were excluded.

Overall, there were 12,437 participants aged ≥ 19 years who were eligible for data analysis (Fig. 1). The Institutional Review Board of Yongin Severance Hospital waived the requirements for

approval and consent because the analyses of the present study were based on de-identified, publicly available secondary data. MEASURES PATIENT HEALTH QUESTIONNAIRE (PHQ-9) The patient

health questionnaire (PHQ-9) is a 9-item questionnaire that assesses the severity of depression with a total score ranging from 0 to 27. Each of the nine questions is scored between 0 (not

at all) to 3 (nearly every day) and has been considered to be a reliable and valid measure to screen depression severity. Regarding the assessment of severity, PHQ-9 is comprised of five

categories and cut-off scores of 0–4 indicates no depressive symptoms, 5–9 indicates mild depressive symptoms, 10–14 indicates moderate depressive symptoms, 15–19 moderate-severe depressive

symptoms, and 20–27 indicates severe depressive symptoms39. A validation study of the Korean version of PHQ-9 which reported a cut-off score of 5 for screening depressive symptoms

demonstrated 81.8% of sensitivity and 89.9% of specificity40. Henceforth, in the current study utilizing the Korean version of PHQ-9, the cut-off score of 5 was also applied to identify the

minimal level of depressive symptoms within the participants. Depression, according to DSM-5 criteria, is clinically met when five of the nine psychiatric symptoms are exhibited by the

individuals during a 2-week period with at least one symptom being depressed mood or loss of interest41. In contrast subsyndromal depressive symptoms may not meet the criteria of a clinical

disorder yet are associated with increased risk for the development of major depression or impairment42. Henceforth there are differences in the nomenclature of depressive symptoms and

depression. For this study, depressive symptoms of precarious employees were assessed. EXERCISE AND SLEEP Participants were assessed regarding their weekly exercise levels. Three different

categories of exercises were evaluated which included aerobic exercise, strength exercise, and walking. Each participant was asked to answer a self-report measure, which included the number

of days per week that they exercised for more than 10 min per session according to the type of exercise (strength, aerobic, and walking exercise). Strength measures included questions

regarding whether the participants have done any form of exercise involving the muscles, including push-ups, sit-ups, weightlifting, pull-ups, etc. Any participants who have performed these

exercises more than once per week were considered as undertaking regular physical activity whereas those who performed once or less were considered as non-exercising participants. Similar

methods of assessment on exercise were conducted to assess the type of exercise that were associated with depression with a PHQ-9 cut-off score set at 10, demonstrating a significant

association22. After assessing the exercise frequency and categorizing these into binary groups, the participants were then regrouped into those engaging in no form of exercise, one form of

exercise, or two or more variations of exercise. Sleep duration was self-reported, and participants were asked “how many hours of sleep do you usually get in a day on average?” From the

responses, the durations were categorized as < 6 h/day, 6 to < 9 h/day, and ≥ 9 h/day. The questions and categories were in line with existing research association sleep duration and

physical health within the South Korean adult population43. COVARIATES Demographic details (age and residential area), socio-economic status (education level, household income and marital

status), and additional health-related variables (body mass index, smoking status, alcohol consumption and metabolic syndromes were assessed as covariates for the current study. The

metabolic syndrome diagnosis was based on the recommendations of the presence of 3 or more of the following 5 abnormalities, (i) central obesity (waist circumference > 90 cm for men and 

> 80 cm for women); (ii) hypertension (blood pressure ≥ 140/90 mmHg or consuming antihypertensive drug treatment); (iii) hyperglycemia (fasting glucose level of serum ≥ 100 mg/dL or use

of antidiabetic medication); (iv) high triglyceride (TG) levels (TG ≥ 150 mg/dL or drug treatment for dyslipidemia); or (v) low high-density lipoprotein cholesterol (HDL-C) levels (< 40 

mg/dL among men and < 50 mg/dL among women). STATISTICAL ANALYSES General characteristics of the participants were assessed using Chi-square tests. Multivariable logistic regressions

examined the relationship between exercise variation and depressive symptoms. Subgroup analyses were also conducted to investigate the combined effects of exercise variation and the

covariates on depressive symptoms. SAS software (version 9.4; SAS Institute, Cary, North Carolina, USA) was used for the analyses with a p-value of < 0.05. DATA AVAILABILITY This study

analysed data from the 2014, 2016 and 2018 KNHAES. All the KNHANES data are available to the public and can be downloaded from the KNHANES official website (http://knhanes.cdc.go.kr/).

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6-2020-0165) of the Yonsei University College of Medicine. The funding body had no role in the study design, data collection and analysis, decision to publish, or preparation of the

manuscript. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Department of Psychiatry, Yongin Severance Hospital, Yongin, South Korea Jae Won Oh, Jin Young Park & San Lee * Mind Health

Clinic, Yongin Severance Hospital, Yongin, South Korea Jae Won Oh & San Lee * Department of Psychiatry and the Institute of Behavioral Science in Medicine, Yonsei University College of

Medicine, Seoul, South Korea Jin Young Park & San Lee Authors * Jae Won Oh View author publications You can also search for this author inPubMed Google Scholar * Jin Young Park View

author publications You can also search for this author inPubMed Google Scholar * San Lee View author publications You can also search for this author inPubMed Google Scholar CONTRIBUTIONS

J.O., S.L. and J.P. led the study conceptualisation and design. J.O. and S.L. performed statistical analyses and interpretation. J.O. wrote the first draft of the manuscript and S.L.

reviewed and edited the drafts. All authors have full access to all data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

CORRESPONDING AUTHOR Correspondence to San Lee. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing interests. ADDITIONAL INFORMATION PUBLISHER'S NOTE Springer

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visit http://creativecommons.org/licenses/by/4.0/. Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Oh, J.W., Park, J.Y. & Lee, S. Association between exercise variations

and depressive symptoms among precarious employees in South Korea. _Sci Rep_ 11, 15952 (2021). https://doi.org/10.1038/s41598-021-95383-y Download citation * Received: 16 April 2021 *

Accepted: 26 July 2021 * Published: 05 August 2021 * DOI: https://doi.org/10.1038/s41598-021-95383-y SHARE THIS ARTICLE Anyone you share the following link with will be able to read this

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