Long workhour has become an important issue over the past few years in Korea. Koreans worked the second longest hours (2,124 hours per year in 2014) according to the Organization for Economic Cooperation and Development (OECD) report [1]. The Korean government implemented the new Labor Standards Act to limit the maximum work hours per week from 68 to 52 hours in 2018 [2]. Adverse health effects of overtime work have been investigated in recent studies. It has been shown that overtime work can increase risk of weight gain [3], atrial fibrillation [4], and metabolic syndrome [5]. The longer the work hour, the higher the risk of stroke and coronary heart disease [6]. Long work-hour is associated with psychologic factors such as depression, anxiety symptoms [78], and reduced sleep quality [910]. It also adversely influences worker's family [1112]. Furthermore, overtime work is related to higher occupational injuries than jobs without having long workhours [1314].

After the Korea financial crisis in 1997, divorce risk has increased at a rapid speed [15]. Divorce, one of the most traumatic events in life, has negative physical influences. It can induce considerable risk for all-cause mortality and significantly increase the risk for early death compared to married counterparts [16]. Divorced men and women are known to have higher risk of suicide [1718]. Divorce not only negatively impacts divorced men and women themselves, but also increases risk of early alcohol initiation [19], depression, and social functioning of in adolescence of their children [20].

Compared to male workers, female workers in Korea are generally responsible for most of the housework [2122]. OECD reported that females spent more hours caring for their children than males, with the largest differences in Korea [23]. Although women's marital satisfaction was negatively associated with their household affair burden in Korea as already seen in Western countries, Korean women often experienced conflicts with their husbands about housework because housework was not equally distributed in Korea compared to that in China [24].

Various factors including shift work [25], depression [26], and financial strain [27] can negatively influence marital stability. However, the relationship between working time and the negative impact on marital status change such as divorce or separation has not been studied in Asian countries strongly influenced by Confucianism such as Korea [28]. Therefore, the objective of this study was to investigate the association between long workhours and marital status change by sex in Korea.

The study group consisted of 8,346 (20.5%) female participants and 32,308 (79.5%) male participants. Age, educational status, total monthly household income, weekly workhours, working type, and depression were significantly different between female and male workers (Table 1). Proportions of above college graduates in females and males were 80.8% and 90.3%, respectively. Above 60% of females and males earned more than 6 million KRW per month. The highest percentage of weekly workhours was working ≤ 40 hours in females (64.8%) and working 41–52 hours in males (43.6%).

Age, educational status, total monthly household income, and working type were significantly different and associated with the categories of weekly workhours in both females and males (Tables 2 and 3). The proportion of weekly workhours less than or equal to 40 hours was higher in older, less educated, lower total monthly household income, non-daytime, and non-depressive group in females and males. The proportion of long working hours over 60 hours a week was higher in younger, less educated, higher total monthly household income, non-daytime, and depressive group in females and males.

The number of divorced or separated females and males were 32 (0.383%) and 74 (0.229%), respectively from 2014 to 2015 (data not shown). In both females and males, total household earning per month and depression were significantly associated with marital status change. Divorce or separation risk were statistically higher in those whose monthly income was < 6 million KRW and those who were depressive in females and males (data not shown). Table 4 shows the relationship between weekly workhours and the risk of marital status change from married to divorced or separated status (Table 4). When working ≤ 40 hours a week was considered as a reference group in the crude model, ORs (95% CI) of marital status change for working more than 60 hours were 4.26 (1.25–14.5) in females and 1.07 (0.40–2.85) in males, respectively. In Model 1 after adjusting for age, total household income per month, and working type, ORs (95% CI) for working more than 60 hours were 4.53 (1.01–20.3) in females and 1.61 (0.58–4.46) in males. In Model 2 after adjusting for variables of Model 1 plus depression, ORs (95% CI) for workhours more than 60 hours were 4.57 (1.02–20.5) in female workers and 1.55 (0.55–4.35) in male workers, respectively. Female workers working for more than 60 hours per week had statistically significant associations with marital status change after adjusting for covariates with a significantly positively linear trend dose-response relationship (p for trend = 0.043).

This study showed the association between average weekly workhours and marriage dissolution of Korean female workers from 2014 to 2015. Working for more than 60 hours per week was significantly associated with marriage change to divorce or separation after adjusting for confounding variables with a dose-response relationship in female workers.

ORs of marital status change for working more than 60 hours per week increased in Model 1 and Model 2 compared to the crude model in females. While four confounding factors were considered one by one, only total monthly household income more than or equal to 6 million KRW decreased the risk of marital status change. Therefore, ORs of marital status change increased in Model 1 compared to the crude model increased because of total monthly household income. ORs of marital status change in Model 2 compared to Model 1 after considering depression because depressive subjects could reduce their workhours and shortened workhours could decrease the risk of divorce or separation. Thus, total monthly household income could decrease the risk of divorce or separation and depression status could have a negative influence on marital status change through workhours in females. Further studies considering interaction among diverse confounders between long workhours and marital status change are needed.

A panel study tracking for three years from the beginning of marriage in America have reported no significant relation between workhours and divorce risk in male workers [30]. However, long workhours increased the probability of divorce in female workers [30]. Also, a retrospective study from the Netherlands has suggested that longer workhours is associated with greater risk of divorce in females but lower risk in males during the first year of marriage [31]. However, the overtime work group of males (≥ 50 hours per week) and females (≥ 40 hours per week) did not show statistically significant difference in divorce risk compared with the non-overtime work group of males (< 50 hours per week) and females (< 40 hours per week), respectively [31]. Results of our study are consistent with results of the above 2 studies, reporting that long workhours could increase the likelihood of divorce or separation in females in a dose-dependent way, not in males. We classified weekly workhours into 4 groups which was more detailed than the Netherlands study. Our study showed that overwork (> 60 hours per week) increased the risk of divorce and separation.

Although how overwork could increase marriage breakdown in females is not fully comprehended yet, several hypotheses have been proposed. First, for female workers, time spent on work is the exchange of time used for their family because women are more likely to be in charge of household affairs and child care than men [223032]. Couples are under more pressure within the household when both have no time to dedicate to each other or to family affairs [30]. Women's overtime working means the lack of family time which is necessary for improving communication and attachment between wife and husband [3133]. Korean women experience more conflicts with their spouses regarding to housework [24]. Also, time difference spent on caring for their children is the largest in Korea [23]. Females working long hours in Korea might gain shorter family interaction time than female in other countries. Second, female workers financially independent from their spouses can easily break their marriage because their enough resources can help them escape from a bad marriage [3034]. Also, financial strain has partial responsibilities for the divorce risk [31]. However, our study showed that females earning more than or equal to 6 million KRW per month had significantly lower risk of divorce or separation than those making less than 6 million KRW per month, even though total monthly household income of females might be their husbands' income (data not shown). The study subjects of 85.3% in females and 87.7% in males earned more than or equal to 4 million KRW per month. Compared to this study population, in the fourth Korean Working Conditions Survey in 2014, general Korean workers aged not less than 20 graduated college or above (50.8%) and earned more than 3 million KRW per month (23.4%) [35]. Thus, our study population may not represent other general Korean workers and further studies about the relationship between total monthly income and the risk of divorce are necessary. Finally, overtime work is associated with depression status [78]. Also, depression could have a bad influence on the stability of marriage [26]. Therefore, long workhours might increase the risk of marital status change through depression. Our results also determined that depressive women had significantly higher risk of divorce or separation than those not depressive (data not shown).

Other factors such as the presence of children and spouses' weekly workhours could affect the probability of divorce. Couples with children have lower risk of divorce than couples without children [31]. However, the effect of overtime work on marital instability is different by sex when there is the presence of children. An additional worktime by men decreases divorce risk, but an additional worktime by women increases divorce risk [30]. The risk of divorce is much higher in both spouses having jobs than in only one having a job [30]. Unfortunately, we were not able to consider the presence of children and spouses' workhours per week because our data did not include information about children and could not match the information between spouses. In this study, only after adjusting for age, working type, total monthly financial income, and depression, working for more than 60 hours a week still significantly increased the risk of divorce compared to working for less than or equal to 40 hours a week. Thus, further research considering the presence of children and spouses' weekly workhours is needed to understand the risk of divorce or separation.

Some limitations of this study should be considered. First, subjects of this study were mostly highly educated and middle-aged Koreans who underwent health check-ups on regular basis. Therefore, our results may not be generalized to other age groups, or less educated groups, or populations with different demographical factors. Second, marital status was primarily determined by a self-reported questionnaire which might be underestimated. Although there were a few limitations, this was one of few studies to identify the association between weekly working time and marital breakdown in Asian countries influenced by Confucianism to the best of our knowledge. In addition, a comprehensive inclusion of potential confounding factors including household earning, working type, and depression strengthened findings of this study, even though there are other confounding variables to consider.

In conclusion, our study indicated that long workhours could increase the risk of divorce or separation in women after adjusting for various confounders in a sample of highly educated and middle-aged Koreans. This association was only revealed in female workers, not in male workers. Since our study only observed the follow-up of marital status change after 1 year, long term follow-up of marital status changes with reducing aforementioned limitations is needed in the future to determine the association between weekly long workhours and marital status change.