A meta-analysis of large prospective cohort studies published in The Lancet, states that working long hours might increase the risk of stroke significantly. Long hours of work also increased the risk of heart disease, although the correlation is less convincing.

According to the International Labor Office study report, about 1 in 5 workers around the world were working more than 48 hours a week in 2007. Overwork is known to lead to a vicious cycle of an unhealthy lifestyle, stress, problems in relationships, etc. Chronic stress is known to cause physical and mental illnesses. As some studies report, there exists a clear correlation between job stress and heart health as well as stroke. Overwork and stress have led to deaths and in fact, in Japanese, there is a specific word called “karōshi,” which literally translates to “death from overwork.”

Although quite a few studies have been conducted in different groups (Example, students, doctors, etc.) regarding a relationship between long hours of work and heart diseases, very few reports exist which are from large studies and include stroke in their assessments. The study being discussed here attempts to plug this gap in knowledge.

The scientists collected published and unpublished data from various resources and put together a collective database. There were data from 20 unpublished cohort studies as well as 25 studies from 24 cohorts from Europe, USA, and Australia. The data sets were as follow:

• The meta-analysis for coronary heart disease comprised 603,838 men and women, who were free from coronary heart disease at baseline. They were followed for an average of 8.5 years.
  
• Similarly, for stroke, the study analyzed 528,908 men and women who were free from stroke at baseline. These individuals were followed for an average 7.2 years.

The data were adjusted for age, sex and socio-economic status. Analysis of follow-up studies showed that:

• Working long hours (55 hours or more per week) compared to standard working hours (35-40 hours per week) was associated with a slightly increased risk of incident coronary heart disease.
  
• Working long hours significantly increased the risk of stroke when compared to standard working hours.
  
• The risk of stroke increased with the number of extra hours worked.
  

       o   Working up to 48 hours per week increased the risk by 10%

       o   Working up to 54 hours per week increased the risk by 27%

       o   Working over 55 hours per week raised the risk of stroke to 33%

The authors conclude, “Employees who work long hours have a higher risk of stroke than those working standard hours; the association with coronary heart disease is weaker. These findings suggest that more attention should be paid to the management of vascular risk factors in individuals who work long hours.”

As reported by the BBC, the lead author of the study, Dr. Kivimiki says, "People need to be extra careful that they still maintain a healthy lifestyle and ensure their blood pressure does not increase."

Dr. Tim Chico, a consultant cardiologist from University of Sheffield, says to BBC, "Most of us could reduce the amount of time we spend sitting down, increase our physical activity and improve our diet while working and this might be more important the more time we spend at work."

So, is “karōshi” avoidable? Many studies show that eating healthy, staying active, and adopting some simple means to heighten one’s mood could pave the way for a stress-free, healthy and therefore, longer life.

Written by Mangala Sarkar, Ph.D.

Primary Reference

Kivimaki, M., Jokela, M., Nyberg, S., Singh-Manoux, A., Fransson, E., Alfredsson, L., . . . Virtanen, M. (2015). Long working hours and risk of coronary heart disease and stroke: A systematic review and meta-analysis of published and unpublished data for 603 838 individuals. The Lancet. Retrieved August 21, 2015, from http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(15)60295-1/fulltext

DoveMed Resources

Brain Stroke. (n.d.). Retrieved August 21, 2015, from http://www.dovemed.com/brain-stroke/

Simple Ways to Naturally Heighten Your Mood. (n.d.). Retrieved August 21, 2015, from http://www.dovemed.com/healthy-living/wellness-center/simple-ways-naturally-heighten-your-mood/

Additional References

(n.d.). Retrieved August 21, 2015, from http://www.ilo.org/wcmsp5/groups/public/@dgreports/@dcomm/@publ/documents/publication/wcms_104895.pdf (Routledge Studies of modern world economy, 2007)

Case Study: Karoshi: Death from overwork. (2013, April 23). Retrieved August 21, 2015, from http://www.ilo.org/safework/info/publications/WCMS_211571/lang--en/index.htm

Stress and Heart Health. (n.d.). Retrieved August 21, 2015, from http://www.heart.org/HEARTORG/GettingHealthy/StressManagement/HowDoesStressAffectYou/Stress-and-Heart-Health_UCM_437370_Article.jsp

Fransson, E., Nyberg, S., Heikkilla, K., Alfredsson, L., Bjorner, J., Borritz, M., . . . Kivimaki, M. (2015). Job strain and the risk of stroke: An individual-participant data meta-analysis. Stroke, 46(2), 557-559.

Stroke 'more likely' with long hours - BBC News. (n.d.). Retrieved August 21, 2015, from http://www.bbc.com/news/health-33986250