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HEALTHY
Long Working Hours and Risk of Nonalcoholic Fatty Liver Disease: Korea National Health and Nutrition Examination Survey VII
This is an open-access article distributed under the terms of the creative Commons Attribution License ( CC BY ). The function, distribution or reproduction in other forums is permitted, provided the master generator ( s ) and the copyright owner ( s ) are credited and that the master publication in this journal is cited, in accordance with bear academic rehearse. No use, distribution or reproduction is permitted which does not comply with these terms. The preponderance of NAFLD ( HSI ≥36 ) increased with longer working hours : 23.0 %, 25.6 %, and 30.6 % in the 36–42, 43–52, and 53–83 hours/week group, respectively ( p < 0.001 ). Subjects who worked 53–83 hours/week had higher odds for NAFLD than those who worked the standard 36–42 hours/week ( OR 1.23, 95 % CI 1.02–1.50, p = 0.033 ) after adjusting for long time, sex, body multitude index, smoke, alcohol, exercise, diabetes mellitus, high blood pressure, serum triglyceride, and total cholesterol. This association was reproducible across subgroups according to working agenda ( day vs. switch workers ) or occupation character ( function vs. manual workers ). In finical, the relationship between long working hours and NAFLD was pronounced in workers aged < 60 years and in female workers. NAFLD is a leading induce of liver disease with a global prevalence of ~ 25 % ( 7, 8 ). The disease load of NAFLD is expected to rise aggressively global as the incidence of fleshiness, diabetes mellitus, and metabolic syndrome—conditions with a well-established affiliation with NAFLD—is increasing ( 9 ). As working long hours heightened the risk of such conditions, it may besides increase the gamble of NAFLD. however, to our cognition, no previous studies have reported the association between long working hours and NAFLD. To fill this research gap, this analyze aimed to assess the relationship between retentive working hours and NAFLD by analyzing data from a big population-level survey. R adaptation 3.4.0 software and the R libraries survey, RODBC, car, and Cairo were used for data analysis ( R Foundation for Statistical Computing, Vienna, Austria ; available at hypertext transfer protocol : //www.R-project.org ). All statistics were calculated using sample distribution weights assigned to sample participants by the KNHANES. The sample weights were constructed to attain indifferent estimates representing the entire korean population, with circumstance of the stratify multistage probability sampling design of each review year. continuous variables are presented as medians with interquartile ranges, and categorical variables are presented as frequencies with weighted percentages. The chi-square test was used to compare the preponderance of NAFLD according to working hours. Associations between NAFLD and working hours were analyzed using multivariable logistic regression models adjusting for confounding factors such as age, sex, fume, alcohol, BMI, comorbidities ( diabetes mellitus defined as previously diagnosed as diabetes mellitus or receiving glucose-lowering treatment, and high blood pressure defined as previously diagnosed as high blood pressure or receiving blood pressure-lowering medicine ), serum triglyceride, and serum total cholesterol. Differences with p < 0.05 were considered statistically significant.
Subjects were grouped according to their solve hours by 36–42, 43–52, and 53–83 hours/week, as previously described ( 16 ). They were besides categorized to “ day workers ” if they worked chiefly between 6 am and 6 promethium and to “ shift key workers ” if they worked in any other schedule for subgroup analyses. furthermore, occupations were grouped into “ position employment ” ( managers, professionals and relate experts, clerks, service workers, and sales workers ) and “ manual function ” ( agricultural/forestry/fishery workers, skilled workers, device and car operators, and elementary manual workers ). KNHANES collects information on occupation through an interview conducted by a train aesculapian staff and interviewers ( 15 ). The subjects disclose their average working hours per week including overtime and night shifts as an assailable question. They besides provide their working agenda by choosing among 1 ) working in day ( between 6 am and 6 phase modulation ), 2 ) ferment in the afternoon ( 2 promethium to midnight ), 3 ) working at night ( 9 promethium to 8 am the following day ), 4 ) work in rotation shifts ( day to night ), 5 ) work on understudy days, 6 ) employment in split shifts ( more than two batch timeslot a day ), or 7 ) irregular shifts. then the subjects answer whether they work as managers, professionals or relate experts, clerks, servicing workers, sales workers, agricultural/forestry/fishery workers, skilled workers, device and machine operators, or elementary manual workers. Subjects besides disclose whether they are freelance, employees, or amateur family workers. The presence of NAFLD was assessed using HSI. HSI is a well-validated prediction model for determining NAFLD and is calculated using the pursue convention : HSI = 8 alanine aminotransferase/aspartate transaminase ratio + body batch index ( BMI ) + 2 if diabetes + 2 if female ( 11 ). An HSI index of > 36 was considered to indicate the presence of NAFLD. former studies have validated this scoring system using liver biopsy, abdominal sonography, proton magnetic resonance, and controlled attenuation argument measurement in large samples, and showed a good correlation coefficient between HSI and the degree of NAFLD ( 12 – 14 ). A sum of 10,677 subjects aged 19 – 80 years who are presently working were initially screened ( auxiliary Figure 1 ). Subjects who met the follow criteria were excluded : 1 ) unavailable data on working hours or working schedule ; 2 ) engaged in half-time ferment ( < 36 hours/week, according to the criteria of the Korea Labor Institute ( 10 ) ) or in highly long working hours ( > 83 hours/week, army for the liberation of rwanda exceeding the legal limits ) ; 3 ) former diagnosis of hepatitis B, hepatitis C, or liver-colored cirrhosis ; 4 ) dense alcohol consumption ( ≥2 drinks per workweek with an average of ≥7 alcohol units at a time for men and ≥5 alcohol units at a time for women ) ; and 5 ) any miss argument for calculating the liverwort steatosis index ( HSI ). ultimately, 5,661 subjects were included in the analyze, representing 14,121,493 Koreans. Data were obtained from the Korea National Health and Nutrition Examination Survey ( KNHANES ), a countrywide cross-sectional survey conducted by the Korea Centers for Disease Control and Prevention to provide national health, diet, and nutriment data representing the civilian, noninstitutionalized korean population. Data from interpretation VII, the latest survey conducted from 2016 to 2018, were used for this study. Research subjects were selected using two-stage stratify bunch sample distribution of the population and housing census data. The data were collected via family interviews and standardized physical examinations. Informed accept was obtained from each participant before performing the sketch, and secondary anonymized data were used in the analyses. The Korea University Institutional Review Board approved the study protocol in accord with the Declaration of Helsinki by the World Medical Association. far logistic arrested development was performed with stratification of subgroups by senesce ( < 60 vs. ≥60 years ), sex ( male vs. female ), working agenda ( day vs. chemise workers ), and occupation type ( function vs. manual of arms workers ) ( ). All p-values for interaction were not meaning. No differences were observed according to working schedule or occupation type. The association between NAFLD and working hours was significant in subjects aged < 60 years and in female subjects. Multivariable logistic regression was performed to assess the association between working hours and NAFLD after adjusting for common confounding covariates for NAFLD ( ). The minimally adjusted model with historic period and sexual activity ( model 1 ) showed a importantly higher OR for NAFLD of 1.34 ( 95 % CI 1.13–1.59, phosphorus < 0.001 ) in the 53–58 hours/week group than the 36–42 hours/week group as the reference. The association was besides significant after adjusting for senesce, arouse, smoke, alcohol, practice, BMI, history of previous diabetes mellitus or high blood pressure, serum triglyceride, and serum sum cholesterol with an OR of 1.23 ( 95 % CI 1.02–1.50, p = 0.033 ; model 2 ). After far adjust for working agenda ( day vs. good afternoon vs. night vs. regular shifts vs. irregular shifts ), type of use ( freelance vs. employee vs. unpaid class worker ), and sleep duration ( < 5 hours/day vs. 5–6 hours/day vs. ≥7 hours/day ), the 53–58 hours/week group still had higher OR for NAFLD of 1.23 ( 95 % CI 1.00–1.50, phosphorus = 0.046 ; model 3 ).
A potent association was observed between working hours and HSI by quartiles based on working hours ( p < 0.001, ). like results were observed for BMI, aspartate transaminase, and alanine transaminase levels by quartiles in relation back to working hours ( all p < 0.001, Supplementary Figures 2A–C ). By using the cutoff level of 36, the preponderance of NAFLD ( HSI ≥36 ) besides importantly differed among the three groups : 23.0 %, 25.6 %, and 30.6 % of subjects with NAFLD in the 36–42, 43–52, and 53–83 hours/week groups, respectively ( ). Working patterns and sleep duration according to three groups based on working hours ( 36–42, 43–52, and 53–83 hours/week ) are presented in Supplementary Table 1. Subjects working 36–42 hours/week had higher proportion of subjects working at day ( 89.0 % ) than those working 43–52 ( 88.0 % ) or 53–83 ( 82.1 % ) hours/week. In addition, subjects working long hours were largely freelance as 45.9 % of the freelance subjects worked 53–83 hours/week and only 25.1 % of them worked standard hours ( 36–42 hours/week ). On the other hand, in employees, most of them ( 42.3 % ) worked criterion hours and merely 21.4 % of them worked over 53 hours/week. As expected, subjects working long hours had shorter duration of sleep than those working standard hours. The baseline characteristics of the cogitation subjects according to the presence of NAFLD are summarized in. Among 5,661 subjects, 1393 ( 24.6 % ) had NAFLD based on HSI. The medial long time was 46 years in both groups. work force accounted for 56.6 % of the subjects without NAFLD but accounted for a importantly higher proportion ( 74.6 % ) of those with NAFLD ( phosphorus < 0.001 ). Higher BMI and higher prevalence of diabetes mellitus or high blood pressure were observed in subjects with NAFLD than in those without. The median bring hours per week were 47 hours/week in the NAFLD group and 45 hours/week in the non-NAFLD group. significant differences were noted in working schedule and type of use but not in occupation type between the two groups. Subjects without NAFLD slept longer hours compared with those with NAFLD .
Discussion
This nationally example data showed that long work hours are associated with higher odds of NAFLD in workers without previous liver disease or heavy alcohol drinking habits. The prevalence of NAFLD increased as the work hours per week increased. Subjects who work 53–83 hours/week had 1.23 times higher OR for NAFLD than those working the standard 36–42 hours/week, independent of known gamble factors for NAFLD. excessive working hours pose a serious danger to the health of workers. Concerns about the health status of workers are increasing, as many negative effects of long running hours are continuously being reported. In a meta-analysis, long working hours were associated with an increased risk of coronary center disease and stroke compared with standard working hours ( 2 ). Besides the well-established risk for cardiovascular disease in individuals who work long hours, risks for assorted work-related metabolic diseases, such as fleshiness, high blood pressure, type 2 diabetes mellitus, and metabolic syndrome, have besides been reported. recently, Zhu et alabama. reported that long work hours are associated with obesity-related harmful outcomes in their meta-analysis ( 17 ). Although these metabolic diseases are close related to NAFLD, no previous studies have addressed the association between long working hours and NAFLD. NAFLD is a clinical syndrome characterized by the accumulation of adipose tissue in the liver ( 18 ). It is quickly becoming a major threat for liver-related deaths and a contribute indication for liver transplant ( 19 ), warranting the assessment of the gamble factors for this disease entity. however, NAFLD is normally asymptomatic, making it unmanageable to identify every individuals having NAFLD in general population. besides, liver biopsy is regarded as a gold standard for the diagnosis of NAFLD, which is incursive and therefore may not be appropriate for big epidemiologic studies. The HSI marking system used in this study is a elementary, noninvasive, and well-validated screen tool for NAFLD and thus, widely used in many former studies to assess NAFLD ( 12 – 14 ). One plausible component that may explain the yoke between retentive influence hours and NAFLD would be physical inactiveness in overworking individuals. Working overindulgence hours may limit leisure-time physical natural process and may result in fat collection ( 20 ). sedentary behavior is known to be associated with the risk of NAFLD exploitation, and decreased forcible activity is known to intensify the asperity of NAFLD ( 21 ). unhealthy dietary patterns may besides play a function in increasing the risk for NAFLD. A previous study suggested that long shape hours were associated with poor eating habits such as skipping breakfast, eating out, eating instant food, and overeating ( 22 ). These insalubrious diet patterns were found to be an independent risk factor for the onset of NAFLD ( 23 ). long working hours are besides associated with life style habits such as smoke and alcohol drink ( 24 ). however, the present study demonstrated a robust relationship between long working hours and NAFLD flush after adjusting for confounding life style factors. In addition, work-related rest loss or chronic stress may be other implicit in mechanisms contributing to the development of NAFLD by causing weight acquire via alteration in hormones or energy homeostasis ( 25 ). A former study reported that rest duration was found to have a significant mince impression on working hours and NAFLD ( 26 ). They observed that hazard for NAFLD in long working hour group was higher than standard working hour group alone in subjects sleeping 5 – 6 hours/day and not in those sleeping < 5 or ≥7 hours/day. however, in our study, the negative effect of long work hours on NAFLD was meaning even after adjusting for beggarly sleep duration of the subjects. far studies are necessary to make a clear decision for this publish.
different effects of long work hours on NAFLD were observed across subgroups. While, in subjects aged < 60 years, long working hours amounting to 53–83 hours/week were associated with a significantly higher gamble for NAFLD ( OR 1.52, 95 % CI 1.27–1.83 ) than working hours of 36–42 hours/week, the OR was statistically not significant ( 1.32, 95 % CI 0.87–2.00 ) in a subgroup of subjects aged ≥60 years. According to an epidemiologic review, NAFLD is more common in the younger to middle-aged groups, with a refuse in prevalence at the old age of 50–60 years ( 27 ). The small number of subjects aged ≥60 years who work 53–83 hours/week ( 7.1 % of the sketch subjects ) may have limited this subgroup to reach statistical meaning. The OR for NAFLD was more marked in female workers ( 1.69, 95 % CI 1.23–2.33 ) than in male workers ( 1.21, 95 % CI 0.99–1.48 ). In korean company, women tend to take more familial responsibilities as the primary health professional for children and households ( 28 ). frankincense, full-time working female employees may exhibit poorer health outcomes because of extra family study charge, including preparing meals, clean, and childcare ( 29 ). This may partially explain the higher risk in female workers. however, information on time spent for family jobs is not available in the stream dataset and could not be analyzed. Although statistically not significant, lurch workers had a higher oregon for NAFLD than day workers. Shift work cycle-induced alterations of circadian rhythm method of birth control have been shown to potentiate proinflammatory cytokine formula in adipose tissue vitamin a well as insulin resistance and glucose intolerance in high-fat diet-fed shiner ( 30 ). former studies reported that careen bring is associated with metabolic syndrome ( 31, 32 ). In this manner, switch workers may have higher hazard for NAFLD. Office workers and manual workers had a relatively similar hazard for NAFLD in the confront study. There are some limitations to address. First, because this was a cross-sectional analyze, the ascertained association does not necessarily reflect a causal relationship. second, we used an collateral measurement ( HSI scoring system ) rather than imaging or pathology examinations to define NAFLD. however, as previously mentioned, HSI is a well-validated marking arrangement for predicting the presence and degree of NAFLD in many large-scale studies. The prevalence of NAFLD according to HSI was 24.6 % in this study cohort, which is comparable to the estimated prevalence of NAFLD global, supporting the accuracy of HSI in determining NAFLD. Third, this study could not evaluate the association between long working hours and liver fibrosis by using NAFLD fibrosis score due to lack of data on sealed parameters or fibrosis-4 score due to excessively small count of subjects having significant fibrosis based on the cut-off grade of ≥2.67. fourth, because this analyze included merely the korean population, the results of our cogitation need to be confirmed in other ethnicities in the future. last, although we attempted to adjust for respective possible risk variables, there might be residual confounding factors or diagonal that we could not control, such as detail dietary patterns including components of macro- and micronutrients. Despite these limitations, the present cogitation had noteworthy strengths, including the nationally representative large sample size, standardized high-quality clinical and lab data collection, and comprehensive examination data about respective confounding factors. furthermore, this study identified a significant association between long working hours and NAFLD, which may provide insight into modern mechanisms and strategies for preventing NAFLD. In conclusion, long work hours are associated with a higher risk for NAFLD than standard work hours. This association is more pronounce in workers aged < 60 years and in female workers but is consistent regardless of working agenda or occupation type. Considering the wide range of adverse health outcomes of long work hours, protecting the health of workers through the regulation of working hours may be necessity, particularly to reduce the gamble of NAFLD. Further prospective studies are required to validate the causal relationship and to examine the effects of treatment of modulating the work hours .