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Shift work can affect sleep and increase the risk of suicide. This study attempted to predict suicidal ideation according to shift work by using machine learning techniques.We analyzed a total of 43,095 data conducted by using the 10-year Korean National Health and Nutrition Examination Survey (KHANES). Shift workers and daytime workers were categorized and analyzed using random forest (RF) and decision tree (DT) techniques of machine learning techniques.Shift workers were more than twice as likely to have suicidal ideation as daytime workers. The RF model showed an accuracy of 91.6% for shift workers and 98% for daytime workers. In the DT technique, the rate of suicidal ideation was the highest among shift workers (82.7%) when they were depressed and had an EuroQol-5 Dimension (EQ-5D) score of less than 0.71.Shift work type was evaluated questionnaire and based on screening data, it was not possible to reflect recent changes in the work type and we evaluated for only suicidal ideation for suicide risk factors.The variables influencing the suicide risk of shift workers and daytime workers differ. In the case of shift workers, negative factors such as depression and low quality of life are risk factors for suicide. Efforts are needed to reduce risk factors through administrative and policy interventions to manage workers' health by early screening.

We aimed to analyze the relationship between long working hours and depressive and anxiety symptoms according to gender and shift work.After dividing shift and day workers according to sex, multiple logistic regression analysis was performed to investigate the relationship between weekly working hours and both depressive and anxiety symptoms.Both depressive and anxiety symptoms were significantly higher in weekly working 40 to 52 and more than 52 hours compared with working fewer than 40 hours in female day workers. Male day workers and both male and female shift workers, showed the association between weekly working more than 52 hours and both depressive and anxiety symptoms, compared with working fewer than 40 hours.Our study demonstrated a significant association between long working hours and depression and anxiety symptoms, regardless of gender and shift work schedule.

Hwanjin Park,1 Kounseok Lee2 1Department of Occupational & Environmental Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea; 2Department of Psychiatry, Hanyang University Medical Center, Seoul, Republic of KoreaCorrespondence: Kounseok Lee, Tel +82-2-2290-8423, Fax +82-2-2298-2055, Email dual@hanyang.ac.krPurpose: It has been previously reported that skipping breakfast is positively associated with increased depression, anxiety, stress, and psychological distress. This study examined the effects of breakfast consumption on suicide attempts among adolescents.Patients and Methods: The Korean Youth Risk Behavior Web-based Survey (KYRBWS) is an anonymous self-report survey conducted with middle- and high-school students to understand the health behavior of Korean adolescents. Variables related to suicide risk such as suicide attempts, breakfast frequency, depression, anxiety, and violence were analyzed using multivariate logistic regression analysis. The class selected as the sample class was surveyed for all students and the number of youths selected as the sample in 2020 was 57,925 students from 800 schools (400 middle schools and 400 high schools) in 17 cities and provinces nationwide. Among them, the dataset for this study was 54,948 completed adolescent health behavior surveys.Results: Adolescents who attempted suicide often skipped breakfast and had high stress levels. In the regression analysis, those who ate breakfast less than once a week had a stronger association with suicide attempts than the group of six or seven times a week (OR = 2.186; 95% CI = 1.873– 2.552). In the group of feeling sadness or hopeless for more than two weeks in the past year, those who ate breakfast zero or once a week (OR = 1.269; 95% CI = 1.044– 1.542), or two or three times (OR = 1.300; 95% CI = 1.043– 1.619), showed a stronger correlation with suicide attempts than the group of six or seven times a week.Conclusion: Breakfast can affect adolescents’ emotions. Helping adolescents regularly eat breakfasts might be a suicide prevention strategy.Keywords: breakfast, suicide, depression, risk factors, adolescents

(1) Background: Workers spend most of their days working. One’s working environment can be a risk factor for suicide. In this study, we examined whether suicidal ideation can be predicted using individual characteristics, emotional states, and working environments. (2) Methods: Nine years of data from the Korean National Health and Nutrition Survey were used. A total of 12,816 data points were analyzed, and 23 variables were selected. The random forest technique was used to predict suicidal thoughts. (3) Results: When suicidal ideation cases were predicted using all of the independent variables, 98.9% of cases were predicted, and 97.4% could be predicted using only work-related conditions. (4) Conclusions: It was confirmed that suicide risk could be predicted efficiently when machine learning techniques were applied using variables such as working environments.

There is no study on the relationship between working hours and nonalcoholic fatty liver disease (NAFLD). The objective of the present study was to determine the relationship between working hours and NAFLD by sleep duration using a large set of abdominal ultrasonography examination data. Data from 194,625 patients who underwent health examinations from 2015 to 2017 were analyzed. Chi-square tests, linear-by-linear association and ANOVA were performed to compare general characteristics according to working hours. Multivariate logistic regression analysis was performed to determine the relationship between working hours and NAFLD by sleep duration. There was no significant relationship between working hours and NAFLD prevalence in the group of short sleep duration of ≤5 hours or the group of long sleep duration of ≥7 hours. The risk of NAFLD in the52 working hour group was significantly higher (aOR, 1.09; 95% CI, 1.04-1.14) than that in the 40- to 52-hour working hour group after adjusting for confounding factors in the 5- to 6-hour sleep duration group. There was no significant difference between ≤40 working hours and 40 ~ 52 working hours in the 5 ~ 6 hours sleep duration group (aOR, 1.02; 95% CI, 0.97-1.06). In general, working hours were significantly related to NAFLD. There was a difference in the relationship between working hours and NAFLD according to sleep duration.

Shift work is associated with vitamin D level, sleep quality, and depressive symptoms. Vitamin D and sleep quality are also associated with depressive symptoms. The purpose of this study was to compare vitamin D level, sleep quality, and depressive symptoms between shift workers and daytime workers and analyze the mediating effect of vitamin D and sleep quality between shift work and depressive symptoms. Among those who participated in the Kangbuk Samsung Health Study in 2012 and 2014, 82,078 cases of full-time workers were analyzed. We evaluated their shift work, vitamin D level, sleep quality, and depressive symptoms with blood samples and questionnaires. Chi-square tests, t-tests, and path statistical analysis were performed. More depressive symptoms, lower vitamin D levels, and poorer sleep quality were associated with shift work. According to a path analysis, shift work had both a direct effect and an indirect effect on depressive symptoms, each mediated by sleep quality and vitamin D level. When a multigroup analysis was conducted for each sex, paths containing sleep quality were more significant in female shift workers than male shift workers; paths involving vitamin D did not differ between sexes. To assess depression risk in shift workers, evaluating vitamin D level and sleep quality is essential. Also, sleep problems are more prevalent in female compared to male shift workers with respect depression prevalence.

(1) Background: This study aimed to use machine learning techniques to identify risk factors for suicidal ideation among adolescents and understand the association between these risk factors and socioeconomic status (SES); (2) Methods: Data from 54,948 participants were analyzed. Risk factors were identified by dividing groups by suicidal ideation and 3 SES levels. The influence of risk factors was confirmed using the synthetic minority over-sampling technique and XGBoost; (3) Results: Adolescents with suicidal thoughts experienced more sadness, higher stress levels, less happiness, and higher anxiety than those without. In the high SES group, academic achievement was a major risk factor for suicidal ideation; in the low SES group, only emotional factors such as stress and anxiety significantly contributed to suicidal ideation; (4) Conclusions: SES plays an important role in the mental health of adolescents. Improvements in SES in adolescence may resolve their negative emotions and reduce the risk of suicide.

Background Obesity is a major public health issue. This present study aims to verify the relationship between metabolically healthy obesity (MHO) and suicidal thoughts. Methods Data were collected from a total of 299,594 medical checkup recipients. Frequency analysis and descriptive statistics were used to analyze participants’ general characteristics. To analyze the relationship between metabolic phenotype and suicidal ideation, we computed the cross-ratios after compensating for age, depression, and insomnia by using multivariate logistics regression analysis. Results In an analysis of metabolic phenotype, suicidal thoughts were found to have decreased for moderate waist circumference (74.0–79.1 cm) for women who were >40 years old in the metabolically healthy (MH) group. In contrast, although severe abdominal obesity was associated with increased suicide risk, it was not found to be significantly related to suicide risk when considered together with emotional difficulties such as depression. Limitations This study used only self-report test was conducted to evaluate emotional problems. Conclusions Severe abdominal obesity did not affect suicidal thoughts for either sex when feelings of depression were considered. However, we confirmed that moderate waist circumference could be a protection factor of suicide for those who were >40 years old in the MH group.

Shift work does not synchronize with the 24-hour human circadian rhythm, so shift workers experience various problems related to this disruption. This study investigated the relationship between suicidal risk and emotional difficulties such as depression and anxiety in shift workers according to gender. We analyzed data collected from 79,009 health checkup recipients. We checked psychosocial factors for different genders using the Chi-square test and t-tests. To examine the relationship between shift work and suicidal ideation, we estimated an odds ratio after adjustment for age, depression, and insomnia. There was no difference in terms of the risk of suicidal ideation between shift workers and day workers among women (adjusted odds ratio [AOR], 0.957; 95% confidence interval [CI], 0.826-1.109), whereas the risk of suicidal ideation was significantly higher for shift workers than for day workers among men (AOR, 1.157; 95% CI, 1.021-1.310). This study confirmed that associated factors of shift work-related suicidal ideation could act differently by gender. Shift work for women is generally associated with emotional difficulties such as depression and anxiety, whereas maladaptation to shift work may be related to suicidal ideation among men. A gender-specific suicide prevention approaches will be needed for shift workers.

Shift work directly causes circadian disruption and reduces sleep quality. Physical activity is also associated with sleep quality. However, no study has reported the relationship between a specific level of physical activity and sleep quality. This study aimed to investigate the relationship between sleep quality and the amount of physical activity by stratifying subjects into gender and shift-work subgroups. Among those who participated in the Kangbuk Samsung Health Study in 2016-2017, data from 185,958 full-time workers were analysed. We evaluated their physical activity by metabolic equivalents (METs-min/week), sleep quality and shift work. A chi-squared test, a t test and logistic regression analysis were performed. An increase in sleep quality was found for the group with physical activity of 600-9,000 METs-min/week compared to that in the sedentary group among all subjects. In female day workers, the sleep quality of the group with 600-6,000 METs-min/week was significantly higher (odds ratio [OR], 0.760; 95% confidence interval [CI], 0.673-857) than that in the sedentary group. In male day workers, sleep quality increased when physical activity was increased up to 6,000-9,000 METs-min/week (OR, 0.760; 95% CI, 0.673-857). In female shift workers, there was no significant difference in sleep quality according to physical activity level. In male shift workers, sleep quality was better in the group with physical activity of 1,800-3,000 METs-min/week (OR, 0.826; 95% CI, 0.692-0.986) or 3,000-6,000 METs-min/week (OR, 0.771; 95% CI, 0.642-0.926). Optimal physical activity is good for sleep quality. The sleep quality of females is significantly worse than that of males in both day and shift workers.

Background Over one million Korean night shift workers undergo clinical assessment of sleep using the Insomnia Severity Index (ISI) and Epworth Sleepiness Scale (ESS) by occupational medical examination each year. Therefore, this study was conducted to evaluate the reliability and validity of the ISI and ESS using occupational medical examination data. Methods The study subjects included 12,056 shift workers at an electronics company who underwent an occupational health examination about shift work in 2018. The evaluation of the ISI and ESS was performed using exploratory factor analysis (EFA) and confirmatory factor analysis (CFA). Results According to the results of the EFA, the ISI had a single-factor structure, while the ESS had a two-factor structure, which was inconsistent with the findings of previous studies. The results of the EFA of 15 items from the combined ISI and ESS suggested a three-factor structure, with one factor for ISI items and two factors for ESS items, while the results of the CFA suggested sufficient validity of the combination of the ISI and ESS for sleep evaluation. Conclusion The results suggest that the ISI and ESS have sufficient reliability and validity to be used for occupational health examinations about shift work., Graphical Abstract

Objective Caffeine is the most widely-used psychoactive substance in the world. The present study investigates the relationship between caffeine intake and suicide risk according to gender. Method Analysis of the Kangbuk Samsung Cohort Study (KSCS) data from 80,173 individuals was performed using Chi-square tests and t-tests to determine the relationships between psychosocial constructs and gender. The relationship between caffeine intake and suicidal ideation was analyzed by obtaining odds ratios with multivariate logistic regression in which depression and sleep problems were adjusted for age. Results In both men and women with suicidal ideation, the proportion of those who consume four or more cups of coffee per day was highest among the groups of various coffee intake levels. The results on the relationship between daily coffee intake and suicidal ideation revealed that suicide risk was high in both men and women who consume four or more cups of coffee a day. However, once the age, depression and sleep problems were adjusted for, suicide risk decreased in women of 1–4 cups of coffee intake per day, whereas no change was observed in men. Conclusion Regardless of psychiatric problems such as depression or sleep problems, regular and moderate caffeine intake likely reduces suicide risk as well as depression in women.

Objective: Adult attention deficit/hyperactivity disorder (ADHD) exhibits symptoms, such as attention deficit and impulsivity, that make it difficult for patients to manage social activities. In this study, we investigated the association of adult ADHD symptoms with temperament and character dimensions, taking into account possible sex interactions. Method: A total of 2917 (1462 males and 1455 females) college students completed the 140 5-point Likert items on the Temperament and Character Inventory-Revised Short version (TCI-RS) and the Attention Deficit/Hyperactivity Disorder Self-Rated Scale (ASRS). According to the ASRS score, subjects were classified into the control group, the inattentive ADHD symptom (IA) group, or the hyperactive/impulsive ADHD symptom (HI) group. Additionally, the scores of the four temperament dimensions and the three character dimensions were compared. Results: In the IA and HI groups, the NS and HA levels of the temperament dimension were high and the PS level was low compared with the control group. In the character dimension, the levels of SD and CO were significantly lower in the ADHD groups than in the control group (P

Background Chronotype is individual characteristic, and people who stay up late are acknowledged to be more likely to experience depressive symptoms as well as impulsivity and suicide. Depression is also associated with suicidality. The purpose of this study was to investigate and analyze the role of depression in its effects on chronotype and suicidality. Method A total of 5632 university students were recruited as participants. We evaluated their chronotype, depressive symptoms, and suicidality using questionnaires. Correlation analysis, analysis of covariance, and path analysis were performed. Results Depressive symptoms and suicidality were higher among individuals with an eveningness chronotype: the greater the depressive symptoms, the higher the suicidality. The results of path analysis showed that the direct effect of suicidality in relation to chronotype was not statistically significant, but the indirect effect of depressive symptoms was statistically significant. This result indicates that depressive symptoms fully mediated the relationship between chronotype and suicidality. Conclusion Morningness may be a protective factor, not only against depression but also against suicide. To assess the risk of suicide, we must evaluate not only depressive symptoms, but also the effects of chronotype on depressive symptoms.

Background There is a surge of interest in subjective well-being (SWB), which concerns how individuals feel about their happiness. Life satisfaction tends to be influenced by individual psychological traits and external social factors. The aim of this study was to examine the relationship between individual character and SWB. Methods Data from 3522 university students were analyzed in this study. Character profiles were evaluated using the Temperament and Character Inventory-Revised Short version (TCI-RS). Life satisfaction was assessed using the Satisfaction with Life Scale (SWLS). All statistical tests regarding the correlations between each character profile and life satisfaction were conducted using ANOVAs, t-tests, multiple linear regression models and correlation analyses. Results The creative (SCT) profile was associated with the highest levels of life satisfaction, whereas the depressive (sct) profile was associated with the lowest levels of life satisfaction. Additionally, high self-directedness, self-transcendence and cooperation were associated with high life satisfaction. The results of gender-adjusted multiple regression analysis showed that the effects of self-directedness were the strongest in the assessment of one’s quality of life, followed by self-transcendence and cooperativeness, in that order. All of the three-character profiles were significantly correlated with one’s quality of life, and the character profiles of TCI-RS explained 27.6% of life satisfaction in total. Among the three-character profiles, the self-directedness profile was most associated with life satisfaction. Limitations Our study was cross-sectional, and self-reported data from students at a single university were analyzed. Conclusions The results of this study showed that, among the character profiles, the effects of self-directedness were the strongest for predicting life satisfaction.

Objectives The aim of our study was to elucidate the effect of voluntary/involuntary retirement on individuals’ and spouses’ depressive symptoms using the Korean Longitudinal Study of Aging (KLoSA). Methods This study used a sample derived from the first- to fourth-wave cohort datasets of KLoSA, which was conducted in 2006, 2008, 2010, and 2012. After applying inclusion and exclusion criteria, we analyzed a total of 6706 subjects. Information about employment status, the short-form Center for Epidemiological Studies-Depression scale, and covariates (age, property, household income, perceived health status and medical disability) were obtained. Cox proportional hazards models were used to evaluate the effects of voluntary/involuntary retirement on individuals’ and spouses’ depressive symptoms. Results The voluntary/involuntary retirement groups showed significantly more depressive symptoms than the working group in wave 1–4, and the same results were revealed in the spouse's retirement and job loss measures. The hazard ratios of depressive symptoms of the voluntary/involuntary retirement groups were 1.26–1.31 during the 6 year follow-up period. The wives’ risk of depressive symptoms was also significantly increased if their husbands voluntarily retired (HR = 1.35, 95% CI = 1.10–1.65). Conclusion During the 6 year follow-up study, Voluntary/involuntary retirement increased the risk of depressive symptoms in a Korean elderly population. Furthermore, husbands’ voluntary retirement increased wives’ risk of depressive symptoms.