The association between shift work and the incidence of reflux esophagitis in Korea: a cohort study.

Shift work has adverse health effects such as diabetes, cardiovascular disease, sleep disturbance, depression, and breast cancer. Gastro-esophageal reflux disease (GERD) results in lesions such as reflux esophagitis (RE) and Barrett's esophagus. This study investigated the association between shift work and RE. A cohort study was conducted with 140,553 participants who were followed up at least once from 2012 to 2018. Type of working and shift types were collected using standardized questionnaires. Esophagogastroduodenoscopy (EGD) was performed by experienced endoscopists who were blinded to the aims of this study. According to the Los Angeles classification, RE was categorized based on the extent of esophageal mucosal breaks. During the 469,217.2 person-years of follow-up, 35,185 participants developed incident cases of RE. The multivariable adjusted hazard ratio (95% confidence intervals) for incident cases comparing shift work to fixed day work was 1.09 (1.04-1.13). This association was more strongly observed in the younger age group (18-39 years old) and the female group. In conclusion, shift work was significantly associated with the incidence of RE. Particularly, the results were more significant in the younger and female groups.

Effect of vitamin D deficiency on metabolic syndrome among Korean shift workers.

OBJECTIVE: This study aimed to investigate the effect of vitamin D deficiency on metabolic syndrome among shift workers. METHODS: This study included 207 756 workers who underwent a comprehensive health examination at a large South Korean university hospital between 2012 and 2018. We performed multivariate-adjusted logistic regression analysis and analyzed mediation and exposure-mediator interaction. RESULTS: Overall, 5.5% of the participants had metabolic syndrome. Compared to day work, the odds ratios (OR) of metabolic syndrome and vitamin D deficiency (<12 ng/mL) for shift work were 1.14 [95% confidence interval (CI) 1.06-1.22] and 1.63 (95% CI 1.57-1.70), respectively. Among shift workers, the OR of metabolic syndrome for vitamin D levels of 12-20 and <12 ng/mL, compared with a level of ≥20 ng/mL, were 1.36 (95% CI 1.15-1.61) and 1.51 (95% CI 1.26-1.81), respectively. Shift work and vitamin D deficiency showed an additive interaction; the relative excess risks due to interaction, attributable proportion, and synergy index were 0.26 (95% CI 0.08-0.44), 0.17 (95% CI 0.07-0.28), and 2.09 (95% CI 1.23-3.55), respectively. When vitamin D deficiency was treated as a mediator, the direct and total effects of shift work on metabolic syndrome were 1.12 (95% CI 1.04-1.22) and 1.15 (95% CI 1.07-1.25), respectively. The indirect effect was 1.03 (95% CI 1.02-1.04) and accounted for 18% of the total effect. CONCLUSION: Vitamin D is a potential mediator of the impact of shift work on metabolic risk factors.

Overall and cardiovascular mortality according to 10-year cardiovascular risk of the general health checkup: the Kangbuk Samsung Cohort Study.

Background: According to the occupational accident status analysis in 2020, of 1,180 occupational deaths, 463 were caused by cardiovascular disease (CVD). Workers should be assessed for CVD risk at regular intervals to prevent work-related CVD in accordance with the rules on occupational safety and health standards. However, no previous study has addressed risk and mortality. Therefore, this longitudinal study was conducted to evaluate the relationship between 10-year cardiovascular risk of the general health checkup and mortality. Methods: The study included 545,859 participants who visited Kangbuk Samsung Total Healthcare Centers from January 1, 2002, to December 31, 2017. We performed 10-year cardiovascular risk assessment for the participants and the risk was divided into 4 groups (low, moderate, high, and very high). The study used death data from the Korea National Statistical Office for survival status as an outcome variable by December 31, 2019, and the cause of death based on the International Classification of Diseases, 10th Revision (ICD-10) was identified. Statistical analysis was performed using Cox proportional hazards regression analysis, and the sum of the periods from the first visit to the date of death or December 31, 2019, was used as a time scale. We also performed a stratified analysis for age at baseline and sex. Results: During 5,253,627.9 person-years, 4,738 overall deaths and 654 cardiovascular deaths occurred. When the low-risk group was set as a reference, in the multivariable-adjusted model, the hazard ratios (HRs) (95% confidence interval [CI]) for overall mortality were 3.36 (2.87-3.95) in the moderate-risk group, 11.08 (9.27-13.25) in the high-risk group, and 21.20 (17.42-25.79) in the very-high-risk group, all of which were statistically significant. In cardiovascular deaths, the difference according to the risk classification was more pronounced. The HRs (95% CI) were 8.57 (4.95-14.83), 38.95 (21.77-69.69), and 78.81 (42.62-145.71) in each group. As a result of a subgroup analysis by age and sex, the HRs of all-cause mortality and cardiovascular mortality tended to be higher in the high-risk group. Conclusions: This large-scale longitudinal study confirmed that the risk of death increases with the 10-year cardiovascular risk of general health checkup.

Association between sitting-time at work and incidence of erosive esophagitis diagnosed by esophagogastroduodenoscopy: a Korean cohort study.

Background: Most previous longitudinal studies on lifestyle and gastroesophageal reflux disease (GERD) have focused on physical activity rather than sitting time. The main purpose of this study was to investigate the relationship between prolonged sitting time and the development of erosive esophagitis (EE). Methods: A self-report questionnaire was used for measuring sitting time in the Kangbuk Samsung Health Study. Sitting time was categorized into four groups: ≤ 6, 7-8, 9-10, and ≥ 11 hours/day. Esophagogastroduodenoscopy (EGD) was performed by experienced endoscopists who were unawared of the aims of this study. Hazard ratios (HRs) and 95% confidence intervals (CIs) for the development of EE were estimated using Cox proportional hazards analyses with ≤ 6 hours/day sitting time as the reference. Results: There were 6,524 participants included in the study. During a mean follow-up of 3.14 years, 2,048 incident cases developed EE. In age- and sex-adjusted models, the HR in the group sitting ≥ 11 hours per day compared ≤ 6 hours per day was 0.88 (95% CI: 0.76-0.99). After further adjusting for alcohol intake, smoking status, educational level, history of diabetes, and history of dyslipidemia, sitting time was still significantly related to the risk of EE (HR, 0.87; 95% CI: 0.76-0.98). After further adjustment for exercise frequency, this association persisted (HR, 0.86; 95% CI: 0.76-0.98). In subgroup analysis by obesity, the relationship between sitting time and EE was only significant among participants with body mass index < 25 kg/m2 (HR, 0.82; 95% CI: 0.71-0.95). Conclusions: Generally, prolonged sitting time is harmful to health, but with regard to EE, it is difficult to conclude that this is the case.

The effect of long working hours on developing type 2 diabetes in adults with prediabetes: The Kangbuk Samsung Cohort Study.

Background: Long working hours are known to account for approximately one-third of the total expected work-related diseases, and much interest and research on long working hours have recently been conducted. Additionally, as the prevalence of prediabetes and the high-risk group for diabetes are increasing worldwide, interest in prediabetes is also rising. However, few studies have addressed the development of type 2 diabetes and long working hours in prediabetes. Therefore, the aim of this longitudinal study was to evaluate the relationship between long working hours and the development of diabetes in prediabetes. Methods: We included 14,258 prediabetes participants with hemoglobinA1c (HbA1c) level of 5.7 to 6.4 in the Kangbuk Samsung Cohort Study. According to a self-reported questionnaire, we evaluated weekly working hours, which were categorized into 35-40, 41-52, and > 52 hours. Development of diabetes was defined as an HbA1c level ≥ 6.5%. Hazard ratios (HRs) and 95% confidence intervals (CIs) for the development of diabetes were estimated using Cox proportional hazards analyses with weekly working 35-40 hours as the reference. Results: During a median follow-up of 3.0 years, 776 participants developed diabetes (incidence density, 1.66 per 100 person-years). Multivariable-adjusted HRs of development of diabetes for weekly working > 52 hours compared with working 35-40 hours were 2.00 (95% CI: 1.50-2.67). In subgroup analyses by age (< 40 years old, ≥ 40 years old), sex (men, women), and household income (< 6 million KRW, ≥ 6 million KRW), consistent and significant positive associations were observed in all groups. Conclusions: In our large-scale longitudinal study, long working hours increases the risk of developing diabetes in prediabetes patients.

A case series of flight attendants at risk of COVID-19 in South Korea in 2020.

BACKGROUND: Coronavirus disease 2019 (COVID-19) has infected many individuals worldwide. Individuals in contact with unspecified people during their work, may be at risk of occupational exposure. On June 22, 2020, 1,435 overseas patients were identified in the Republic of Korea. Considering the influx of overseas patients, aircraft-mediated COVID-19 transmission is a major concern. CASE PRESENTATION: We presented two flight attendants diagnosed with COVID-19 who shared the crew's resting area and ground transportation, and discussed the risks experienced by flight attendants. CONCLUSIONS: Biosafety guidelines for cabin crews should be intensified, and their COVID-19 risks must be further investigated. Policymakers must consider comprehensive surveillance systems for workers with high risks of occupational exposures and transmissions, such as flight attendants.

Digital health care and arrhythmia: a case of WPW syndrome in South Korea, 2020.

BACKGROUND: The digital health care field is expanding from the daily monitoring of chronic diseases to the detection of acute diseases, such as arrhythmia. Wolff-Parkinson-White (WPW) syndrome, a congenital cardiac disorder due to accessory pathways, causes tachycardia, syncope, and even sudden death. CASE PRESENTATION: We presented a 26-year-old female office worker with WPW syndrome managing the disease with a wearable device and discussed its significance in occupational medicine. After reviewing the worker's electrocardiogram results, symptoms, and pulse rate records extracted from the wearable device, we referred the worker to a cardiologist for further evaluations such as electrophysiology study. The worker monitors her symptom recurrence with the wearable device following successful radiofrequency catheter ablation of the bypass tract. CONCLUSIONS: A case of an office worker with WPW syndrome managing the disease using a smart watch is presented. Further research is required to ensure its scientific validity, and we suggest policymakers promptly introduce digital health care to occupational environments.

Need for individual-based evaluation to determine the association between humidifier disinfectants and health injuries.

BACKGROUND: Injuries caused by humidifier disinfectants (HDs) can no longer be grouped under the concept of HD lung injury. Focusing on individual cases, we were able to evaluate the relevance not only of diseases for which epidemiological correlation is recognized but also all diseases and symptoms that the victims complain of. METHODS: In-depth interviews and reassessment of 113 HD-exposed patients who had not been acknowledged as victims by the government were conducted, and their medical records were reviewed. Based on these processes, an assessment questionnaire for the injuries related to HDs was completed and the involvement of HDs was assessed either as "strong association," "association," or "no association." RESULTS: In this study, of the 113 patients included who claimed damages, 78 (69.0%) had HD-related injuries. Among the cases of 22 patients who applied for injury acknowledgment due to upper respiratory inflammation that was not included among the acknowledged diseases, 17 (77.3%) were judged to be HD-related injuries (strong association vs. association: 10 [45.5%] vs. 7 [31.8%]). When the cases of 12 rhinitis patients were reassessed, 9 were HD-related injuries (strong association vs. association: 4 [33.3%] vs. 5 [41.7%]). When the cases of 18 asthma patients unacknowledged as a victim were reassessed, 17 (94.4%) were humidifier-related injuries (strong association vs. association: 12 [66.6%] vs. 5 [27.8%]). Among 4 interstitial lung disease patients unacknowledged as a victim, 2 (50.0%) were HD-related injuries. CONCLUSIONS: HD-related health injuries should be assessed through both individual interviews and detailed chart reviews for more accurate injury acknowledgment. In the future, efforts should go beyond existing methods based on the adherence to acknowledgment criteria to directly listen to the victims.

Erratum: Need for individual-based evaluation to determine the association between humidifier disinfectants and health injuries.

[This corrects the article e21 in vol. 33.].

Cross-sectional association between long working hours and endoscopic gastritis: the Kangbuk Samsung Health Study.

OBJECTIVES: This study aimed to determine the cross-sectional association between long working hours and gastritis diagnosed by endoscopy. DESIGN: Cross-sectional study. SETTING: Large university hospitals in Seoul and Suwon, South Korea. PARTICIPANTS: Workers in formal employment who underwent a comprehensive health examination at the Kangbuk Samsung Hospital Total Healthcare Centre clinics in Seoul and Suwon, South Korea, between January 2011 and December 2018. Of the 386 488 participants, 168 391 full-time day workers met the inclusion criteria and were included in the analysis. PRIMARY OUTCOME MEASURE: Endoscopic gastritis. RESULTS: The participants were predominantly college graduates or above (88.9%), male (71.2%) and in their 30s (51.1%), and the median age was 36 (IQR 31-42). Approximately 93.2% of participants had positive endoscopic gastritis, and there was a significant association between working hours and positive findings of endoscopic gastritis. The multivariate fully adjusted prevalence ratio (PR) of endoscopic gastritis for participants working >55 hours per week compared with 35-40 hours per week was 1.011 (95% CI 1.007 to 1.015). Furthermore, endoscopic findings were classified into nine subtypes of gastritis, including superficial gastritis, erosive gastritis, atrophic gastritis, intestinal metaplasia and haemorrhagic gastritis increased with longer working hours (p for trends <0.05). Their PRs for participants working >55 hours per week compared with 35-40 hours per week were 1.019 (95% CI 1.012 to 1.026), 1.025 (95% CI 1.011 to 1.040), 1.017 (95% CI 1.008 to 1.027), 1.066 (95% CI 1.028 to 1.105) and 1.177 (95% CI 1.007 to 1.375), respectively. CONCLUSIONS: Working over 55 hours per week was cross-sectionally associated with positive findings of endoscopic gastritis. The study findings indicated potentially increased risks of superficial gastritis, erosive gastritis, atrophic gastritis, intestinal metaplasia and haemorrhagic gastritis among workers with long working hours (>55 hours per week), supporting the need for further exploration via longitudinal studies.

A longitudinal study of working hours and chronic kidney disease in healthy workers: The Kangbuk Samsung Health Study.

OBJECTIVES: Long working hours are linked to an increased risk of exposure to work safety hazards that threaten the health of workers. To date, only a few cross-sectional studies regarding the relationship between working characteristics, such as over-workload and chronic kidney disease (CKD) have been reported. Therefore, in this longitudinal study, we aimed to examine the direct relationship between long working hours and the incidence of CKD. METHODS: We included 97 856 participants without CKD in the Kangbuk Samsung Health Study. Using a self-report questionnaire, we evaluated weekly working hours, which were categorized into 35-40, 41-52, and >52 hours. CKD was defined as estimated glomerular filtration rate <60 mL/min/1.73 m2 . Hazard ratios (HRs) and 95% confidence intervals (CIs) for incident CKD were estimated using Cox proportional hazards regression analyses with weekly working 35-40 hours as the reference. RESULTS: During a median follow-up of 4.0 years, 185 participants developed incident CKD (incidence density, 4.83 per 104 person-years). Multivariable-adjusted HRs (95% CI) of incident CKD for weekly working >52 hours compared with working 35-40 hours were 1.99 (1.22-3.25). In subgroup analyses, the significant association between working >52 hours and incident CKD was consistently observed in groups of age ≥40 years, men, and obesity with no interaction. CONCLUSIONS: Our large-scale cohort study of young- to middle-aged men and women demonstrated a significant association between long working hours and an increased risk of incident CKD.

Long working hours are associated with a higher risk of non-alcoholic fatty liver disease: A large population-based Korean cohort study.

BACKGROUND: Non-alcoholic fatty liver disease (NAFLD), a common chronic liver disease, may progress to fibrosis, cirrhosis, hepatocellular carcinoma, and liver failure. But only a few cross-sectional studies have reported an association of NAFLD with working hours. This cohort study further examined the association between working hours and the development of NAFLD. METHODS: We included 79,048 Korean adults without NAFLD at baseline who underwent a comprehensive health examination and categorized weekly working hours into 35-40, 41-52, 53-60, and >60 hours. NAFLD was defined as the presence of fatty liver, in the absence of excessive alcohol use, as observed by ultrasound. RESULTS: During a median follow-up of 6.6 years, 15,095 participants developed new-onset NAFLD (incidence rate, 5.55 per 100 person-years). After adjustment for confounders, the hazard ratios (95% confidence interval) for the development of NAFLD in 41-52, 53-60, and >60 working hours compared with that in 35-40 working hours were 1.07 (1.02-1.13), 1.06 (1.00-1.13), and 1.13 (1.05-1.23), respectively. Furthermore, the association remained significant after confounders were treated as time-varying covariates. CONCLUSION: In this large-scale cohort, long working hours, especially >60 working hours a week, were independently associated with incident NAFLD. Our findings indicate that long working hours are a risk factor for NAFLD.

Association between Shift Work and Reflux Esophagitis: The Kangbuk Samsung Health Study.

This cross-sectional study investigated the relationship between shift work and reflux esophagitis verified by endoscopic findings. Participants underwent a comprehensive health examination and esophagogastroduodenoscopy between January 2011 and December 2018. We examined endoscopic findings and performed multivariate-adjusted regression analysis of the association between shift work and reflux esophagitis using multiple demographic and clinical factors. Among the 247,450 participants, 49,767 (20.1%) had reflux esophagitis; Los Angeles (LA)-M (31,132, 12.6%) was most common, followed by LA-A (16,213, 6.6%), LA-B (2333, 0.9%), and ≥LA-C (89, 0.04%). The multivariate-fully adjusted odds ratio (OR) of overall reflux esophagitis for shift work compared to fixed day work was 1.15 (95% confidence interval [CI]: 1.11-1.19). When classified according to shift work type and severity of reflux esophagitis, the ORs of LA-A for regular day and night, and irregular shifts compared to fixed day works were 1.14 (95% CI: 1.03-1.26) and 1.26 (95% CI: 1.11-1.44), respectively. However, there was no significant association between any shift work schedule and ≥LA-B. Overall, we demonstrated the cross-sectional association between shift work (especially rotating and irregular shifts) and mild reflux esophagitis (≤LA-A) compared with daily fixed time shifts.

Cross-sectional association between long working hours and liver function: the Kangbuk Samsung Health Study.

OBJECTIVES: Although the effects of long working hours on liver function remain unclear, in South Korea, there is a social perception that long working hours are associated with poor liver function. Thus, long working hours have recently become a major issue. This study aimed to determine the association between long working hours and liver function, as indicated by the alanine transaminase (ALT) levels. DESIGN: Cross-sectional study. SETTING: Large university hospitals in Seoul and Suwon, South Korea. PARTICIPANTS: Workers in formal employment who underwent a comprehensive health examination at the Kangbuk Samsung Hospital Total Healthcare Centre clinics in Seoul and Suwon, South Korea, between January 2011 and December 2018. Of the 386 488 participants, 212 421 met the inclusion criteria and were included in the analysis. PRIMARY OUTCOME MEASURE: ALT elevation. RESULTS: The participants were predominantly well-educated (86.1%), male (69.3%) and in their 30s (49.6%). In total, 13.4% of the participants presented ALT elevation (>40 IU/L). There was no significant association between working hours and ALT elevation in the general population and in the hepatitis B surface antigen (HBsAg)-negative group. Conversely, in the HBsAg-positive group, working >60 hours per week compared with 35-40 hours per week was significantly associated with ALT elevation. The association was more pronounced in those with ALT levels >80 IU/L (OR 1.94, 95% CI 1.24 to 3.01) than in those with ALT levels >40 IU/L (OR: 1.45, 95% CI 1.20 to 1.75). The p values for trend were <0.05. CONCLUSIONS: Long working hours were associated with ALT elevation only in hepatitis B virus carriers and not in the general population. Provided that there is adherence to the legal working hours, there is no need to further restrict working hours for liver health, irrespective of HBsAg status.

Recommendation for the establishment of a poison control center at the Korea Disease Control and Prevention Agency.

There is currently no governmental body in South Korea resembling the type of poison center (PC) recommended by the World Health Organization (WHO). All Organization for Economic Cooperation and Development (OECD) member countries except for South Korea maintain such a PC tasked with both preventing poisoning accidents and supporting the prompt treatment of poisoned patients. Such a PC could very possibly have allowed the country to more promptly recognize the widespread wave of humidifier disinfectant (HD) associated health effects, including fatal lung injury and death, that lasted started roughly in 2000 and continued through 2011. Despite this chemical poisoning tragedy, South Korea still lacks a surveillance system to monitor health effects caused by the use and consumption of materials that include products containing chemicals, foodborne pathogens, drugs, pesticides, etc. There have been no legal procedures for examining the potential risk of products or materials manufactured by industry. The reporting of national poisoning data or causes of poisoning, which is near ubiquitous in advanced countries with a PC, has not taken place We recommend that a PC should be established within the Korea Disease Control and Prevention Agency (KDCA). In addition, in order to perform surveillance of poisoning cases across the country, a certain number of regional PCs, including at large hospitals, will also be necessary.

Fighting the COVID-19 pandemic: onsite mass workplace testing for COVID-19 in the Republic of Korea.

The ongoing coronavirus disease 2019 (COVID-19) pandemic is causing tremendous damage globally. The Republic of Korea (ROK), a highly export-dependent nation, is a leader in the fight against the COVID-19 pandemic and coping well with the disaster. Like the drive-through COVID-19 testing, which reflects the brilliant flexibility of the Korean medical system, onsite mass workplace testing for COVID-19, which our hospital has been performing over the past few months, is a unique and valuable countermeasure. We believe it is time that the current health examination system for workers in the ROK considered the risk of transmissible diseases.

Mental health impact on a humidifier disinfectant disaster victim: a case report.

In Korea, the cause of lung disease of unknown origin was identified as humidifier disinfectants in November 2011. In February 2017, the 'Special Act on Remedy for Damage Caused by Humidifier Disinfectants' was promulgated. Even though emotional and mental injuries caused by humidifier disinfectants have been reported, the focus of the special act has been on physical injury only, and criteria for recognizing mental health impact have not been considered. This case considers emotional and mental injury caused by humidifier disinfectants. After a humidifier disinfectant was used from January 2005 to April 2006, the patient's son aged 20 months was hospitalized with respiratory symptoms, and he died within two weeks. Also, the patient was hospitalized for a month with the same symptoms, and then she led a normal life with no symptoms. After both mother and son were diagnosed with definite (level 1) humidifier disinfectant lung injury (HDLI) in 2017, she took to drinking alcohol because of extreme guilt over her son's death. In March 2018 she died from acute liver failure due to alcohol use disorder. The patient's death was caused by continuous alcoholism, due to emotional and mental trauma caused by her son's death after HDLI was revealed as the cause. The government did not acknowledge her death was due to humidifier disinfectants, but the company that sold the humidifier disinfectants recognized her as a victim and compensated the family of the victim. There are still lots of psychological responses among humidifier disinfectant disaster victims. Mental health impact on humidifier disinfectant victims should be considered more carefully, and institutional improvements should be made into establish psychological interventions and measures.

Factors associated with anti-hepatitis A virus immunoglobulin G seropositivity among Korean workers: a cross-sectional study.

OBJECTIVES: Hepatitis A incidence in Korea has dramatically increased in recent years. Individuals in their twenties and thirties, who account for majority of the workforce in Korea, are particularly susceptible to infection owing to a low seroprevalence of anti-hepatitis A virus (anti-HAV) immunoglobulin G (IgG). This study aimed to identify behavioural and occupational factors related to anti-HAV IgG seropositivity. DESIGN: Cross-sectional study. SETTING: A large university hospital in Seoul, Korea. PARTICIPANTS: Workers in formal employment having an annual routine health screening. PRIMARY OUTCOME MEASURE: Anti-HAV IgG seropositivity. RESULTS: Of 131 711 individuals who had an annual health screening at the study hospital in 2018, 68 612 met the inclusion criteria and were included in the analysis. Study participants were predominantly men (64.3%) and in their thirties (55.3%). The overall seroprevalence of anti-HAV IgG was 36.2%. In multivariate analyses, anti-HAV IgG seropositivity was independently associated with working in a workplace with ≥2 health managers (vs no health manager, adjusted OR 1.32, 95% CI 1.22 to 1.43); age 40-49 years (vs 20-29 years, OR 2.51, 95% CI 2.36 to 2.68); female sex (OR 1.54, 95% CI 1.48 to 1.59); experience of any general disease (vs no general disease history, OR 1.19, 95% CI 1.14 to 1.25), obesity (vs normal weight, OR 0.91, 95% CI 0.86 to 0.97); and hepatitis B antibody seropositivity (OR 2.39, 95% CI 2.31 to 2.49). CONCLUSIONS: The low prevalence of anti-HAV IgG seropositivity points to a need for implementation of workplace-based hepatitis A vaccine programmes. To promote workers' health and prevent hepatitis A outbreaks, occupational health managers, healthcare providers and policy-makers should focus on individuals who are susceptible to HAV, such as young men.