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Mortality risk
Overall research evidence has shown that long working hours increases mortality risk. A UK census-based longitudinal study of 414949 people aged 20-64 years, showed that overtime work increases mortality risk in men working for more than 55 hours per week. The authors showed that mortality is higher in technical, semi-routine or routine occupations (positions with high demand, low levels of control, or perceived imbalance between effort and reward). The authors also demonstrated that increased mortality risk was mainly attributed to cardiovascular disease.

Similar results were found in other studies. A 30-year longitudinal study in Denmark of 5249 employed Caucasian men aged 40-59 years, showed that men working 41-45 hours per week had a 59% increased risk for mortality due to Ischemic heart disease compared to men working less than 40 hours per week. The authors also found that physical fitness played a significant role, where among men with low physical  fitness, those working more than 45 hours per week had more than twice the risk of death by Ischemic heart disease compared to men working less than 40 hours per week; while this increased risk was not seen among the fittest men. Furthermore, a study based on data from the Swedish twin registry showed that there was an association between overtime work of more than 5 hours a week and increased mortality in women. This association was also seen in men, but only in the first 5 years of follow-up. In contrast, the authors showed that working less than 5 hours a week of overtime decreases the risk of mortality in men.

Counter arguments
Other studies argue that there is no direct cause-and-effect relationship between hours worked and short and long-term risks. Their claims include comments about factors that alter the outcome of effects. These include an individual's personality, occupation, and income. This research was done through a HILDA (Household, Income and Labour Dynamics in Australia) survey in 2001 and was completed in 2004. Prior research into these counter-arguments was completed by a group of researchers in 1997. They found links between increased CVD events and mental health disorder, along with decreases in production, as the number of hours worked increased. However, they state that further research is necessary before definitive conclusions can be made, as factors of each individual have vast consequences on the effect of working overtime. In addition, workers who work overtime when it is not mandatory find that there are very minimal effects on their fatigue levels.

In contrast, a Japanese study of 1105 employees has demonstrated that longer working hours is associated with better health status in older employees. The authors of this study showed that overall health differed by age group, which reflects a generational difference with regards to their attitudes towards work. Among older workers, longer work hours might be beneficial as work-based social networks offer a structured environment, social support, as well as companionship.