Karoshi: Death by Overwork

Catherine Darley, ND

In Japan, karoshi refers to suicides of employees after a period of overwork and work stress. Here in America, many people are working to the extent that their health is damaged and disease states manifest, although not yet to the extent that we have noted a suicide trend.

Who Overworks?

Over the last 2 centuries, work hours have decreased. A landmark event was the passage of the Adamson Act in 1916, upheld by the US Supreme Court in 1917, which standardized the workweek to 40 hours and required employers to pay extra for any additional hours. However, there are plenty of people who work more hours, those either in management roles, those who regularly work “overtime,” or those working 2 jobs. In 2000, about 28% of managers worked 49 hours or more each week, with a higher percentage of men than women.1 That number may have increased in recent years with the economic recession.

A 2006 study2 divided workers into 5 categories based on weekly work hours: part time (1-34 hours), full time (35-40 hours), lower overtime (41-48 hours), medium overtime (49-69 hours), and higher overtime (≥70 hours). (Remember there are 168 hours in a week.) Those working overtime were found more often to be white, middle-aged men with both higher education and income: “They were also more likely to be self-employed, salaried, work as independent contractors, have more than one job, and work split/irregular/on-call shifts.”2(p943)

Overwork, Sleep, and Industrial Accidents

As work hours increase, sleep hours may decrease. Two studies3,4 of long work hours combined with short sleep evaluated industrial accidents. Assessment of the workplace injuries at small to midsized Japanese companies showed a clear increased risk among workers with long workdays (>8 hours per day) compared with those working 6 to 8 hours daily.3 This had a synergistic effect if the person worked long hours and also reported short sleep time of less than 6 hours or other sleep complaints such as sleeping poorly at night, insufficient sleep, or difficulty waking.

Research in America shows a similar relationship. Using the National Health Interview Survey data of 2004 to 2008, it was found that for all workers the overall medically treated, work-related injury rate was 2.80 per 100 workers.4 Those working 31 to 40 hours per week had an injury rate of 2.45 per 100 individuals, while those working the most at over 60 hours per week had an injury rate of 4.34 per 100 people. This study also collected information on sleep, finding the lowest odds ratio for work-related injury of 2.22 among those people sleeping 9 to 9.9 hours daily (though persons obtaining 7-7.9 hours of sleep were close, with an odds ratio of 2.27) and the highest odds ratio of 7.89 in those sleeping less than 5 hours nightly.

Cognitive Performance and Mental Health

Many types of cognitive performance are impacted by work hours. A Whitehall II study5 included 2214 middle-aged British civil servants who were employed full-time at baseline. Follow-up cognitive testing data were collected again about 5 years later. Working 55 hours or more weekly impaired performance in vocabulary and predicted decline in reasoning. The authors stressed the relevance of midlife risk factors on late-life dementia and hypothesized that overwork may contribute.

In another Whitehall II study,6 anxiety and depression were assessed in relation to work hours. Here, working over 55 hours per week was found to increase the risk of anxiety by 1.74 times and the risk of depression by 1.66 times compared with those working 35 to 40 hours per week. This was particularly true for women, more so than for men. In another study,7 those who worked 11 or more hours daily were found to have a 2.43 higher risk of a major depressive episode in the next year, even in the absence of any psychological risk factors at baseline.

Overwork and Cardiovascular Disease

Not surprisingly, food choices and consequently body mass index are also impacted by the number of hours worked. A study8 of metro transit workers showed that men who worked more than 50 hours in a week had worse eating habits (using the vending machines at work more often) and higher body mass index. Interestingly, this was mostly in men. The women who worked greater than 50 hours weekly had the highest intake of fruits and vegetables of all study groups. Other health behaviors are influenced by long work hours and show a sex difference. Additional problems seen in men who work more than 51 hours weekly include poor mental health, smoking, decreased leisure activities, short sleep, and job dissatisfaction; in women who work long hours, complaints include smoking and short sleep.9

Lots of research since 1958 has looked at coronary heart disease and long work hours. A meta-analysis10 was performed that narrowed the investigation to 12 articles. In reviewing all the data, the authors concluded that there is a 40% increased risk of coronary heart disease for those working extended hours. Since this is such a significant leading cause of death, and one seen regularly by physicians, the increased risk deserves attention.

Overwork and Aging

A measure of aging is telomere length. The telomeres are repetitive DNA sequences at the end of chromosomes that provide protection. Short telomeres are associated with health risks, chronic disease, and mortality. In an interesting study,11 it was found that women who currently work full time (40 hours per week) and those who have a longer full-time work history have shorter telomeres than unemployed women.

Naturopathic Care

As NDs, we strive not only to treat disease but also to help create a state of wellness in our patients. I have heard that people who tend to seek out naturopathic care are more educated, with better financial resources than average patients. Therefore, we may be seeing more professionals and managers in our offices, those people who are most at risk for overwork and its myriad health consequences. It may be a good idea to routinely gather information about work hours and work stress, especially if a patient is faced with any of the common conditions mentioned above. I, for one, hope we never need to coin a term similar to karoshi.


Dr Catherine Darley ND

Dr Catherine Darley ND

Catherine Darley, ND is the director of The Institute of Naturopathic Sleep Medicine in Seattle, Washington. The year 2013 marks her 20th year in the sleep field, in varying roles. Dr Darley provides sleep care for people of all ages and specializes in insomnia and circadian rhythm disorders. She also provides sleep education to public groups and health professionals, as well as fatigue management consulting to corporations. Dr Darley currently serves on the executive committee of Start School Later, a national effort to align school start times with circadian physiology of teens. She is a past board member of the Washington Association of Naturopathic Physicians. Dr Darley lives in Seattle with her young family and enjoys sleeping well every night.



  1. Issues in Labor Statistics, U.S. Department of Labor, Bureau of Labor Statistics. Are managers and professionals really working more? May 2000. Summary 00-12. http://www.bls.gov/opub/ils/pdf/opbils37.pdf. Accessed March 21, 2013.
  2. Grosch JW, Caruso CC, Rosa RR, Sauter SL. Long
  3. hours of work in the U.S.: associations with
  4. demographic and organizational characteristics, psychosocial working conditions, and health.
  5. Am J Ind Med. 2006;49(11):943-952.
  6. Nakata A. Effects of long work hours and poor sleep characteristics on workplace injury among full-time male employees of small- and medium-scale businesses.
  7. J Sleep Res. 2011;20:576-584.
  8. Lombardi DA, Folkard S, Willetts JL, Smith GS. Daily sleep, weekly working hours, and risk of work-related injury: US National Health Interview Survey (2004-2008). Chronobiol Int. 2010;27(5):1013-1030.
  9. Virtanen M, Singh-Manoux A, Ferrie JE, et al. Long working hours and cognitive function: the Whitehall II study.
  10. Am J Epidemiol. 2009;169:596-605.
  11. Virtanen M, Ferrie JE, Singh-Manoux A, et al. Long working hours and symptoms of anxiety and depression: a 5-year follow-up of the Whitehall II study. Psychol Med. 2011:1-10.
  12. Virtanen M, Stansfeld SA, Fuhrer R, et al. Overtime work as a predictor of major depressive episode: a 5-year follow-up of the Whitehall II study. PLoS One. 2012;7(1):e30719. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3266289/. Accessed March 21, 2013.
  13. Escoto KH, French SA, Harnack LJ, et al. Work hours, weight status, and weight-related behaviors: a study of metro transit workers. Int J Behav Nutr Phys Act. 2010;7:e91. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3016380/. Accessed March 21, 2013.
  14. Artazcoz L, Cortes I, Escriba-Aguir V, et al. Understanding the relationship of long working hours with health status and health-related behaviors. J Epidemiol Community Health. 2009;63(7):521-527.
  15. Virtanen M, Heikkilä K, Jokela M, et al. Long working hours and coronary heart disease: a systematic review and meta-analysis. Am J Epidemiol. 2012;176(7):586-596.
  16. Parks CG, DeRoo LA, Miller DB, et al. Employment and work schedule are related to telomere length in women. Occup Environ Med. 2011;68(8):582-589.
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