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Accumulated Fatigue May be Considered in the Standards for the Recognition of " Karoshi "

The Expert Examination Meeting of the Ministry of Health, Labor and Welfare (MHLW) gave an outline of a new standards to recognize workers dying from so-called "karoshi" (death due to excessive work) being caused by cerebrovascular or ischemic heart diseases (excluding those attributable to accidental injuries) for the workers' accident compensation insurance.

1. Basic Considerations

(1)      Cerebro-cardio diseases generally appear as a natural process during which pathologic changes develop in blood vessels and continue to progress in aging. However, there are cases in which heavy job-related burdens cause such pathologic changes in blood vessels to become significantly aggravated beyond the natural progressive process, resulting in severe cerebro-cardio diseases.

(2)   As the "accumulation of long-term fatigue" may effect the appearance of cerebro-cardio diseases, the accumulation of fatigue due to long-term work (long-term, excessive burdens) should be considered as a severe and obvious job-related burden, in addition to those burdens that occur during a time period close to the appearance of cerebro-cardio diseases (abnormal events and excessive short-term burdens).

(3)   For supporting the recognition process of a care, it is proper to select a worker in good health condition of similar age, experiences, etc., and a worker who are suffering from the diseases, but he is working without any hindrance.

2. Comprehensive Evaluation of the Excessively Heavy Work Burdens 

(1)      Long-term excessive work burdens

A.    It is reasonable to evaluate the excessively heavy work burdens by specifically and objectively observing working conditions and situations during the six months before the appearance of the relevant cerebro-cardio disease in order to determine whether accumulated fatigue during such period of time is considered to have aggravate pathologic blood vessel changes beyond the natural process, and result in the appearance of such disease.

B.    More specifically, by considering the corelation with the relevant worker's working hours, irregularity of work, work-related restrictions on movement, shift work, working environments and other factors (including the incidence of mental stress) arising from work, a worker may be judged to have undergone excessive burdens when a co-worker of similar age and experience is considered to have experienced such heavy physical or mental burdens.           

C.   With respect to working hours, which are considered to be one of the most important factors causing accumulated fatigue:

(1)   A strong corelation can be assumed between an employee's work and the appearance of a certain disease, if such employee experiences overtime working hours in excess of about 100 hours during the month prior to such appearance, or overtime working hours in excess of about 80 hours per month during the time period of two to six months before such appearance.

(2)   During a time period of one to six months before the appearance,

(a)   if such worker has not experienced overtime-working hours in excess of about 45 hours per month, a corelation between an employee's work and the appearance of a certain disease is considered weak;

(b)   the longer such worker's overtime working hours become in excess of about 45 hours per month, the stronger the corelation between the employee's work and the appearance of a certain disease is assumed.    

D.    Factors other than working hours include the following (see the Appendix for specific examples):

(1)   Irregular working hours

(2)   Long working hours without leave from working place

(3)    Frequent business trips

(4)   Shift work and late-night work

(5)   Working environments (temparature, noise, jet-lag)

(6)   Work-related stress (psychological stress)

(2)      Excessive work burdens in a short period due to abnormal or irregular work situations.

An assumption that obviously excessive burdens due to the work during the period of time close to the appearance of cerebro-cardio diseases can be a direct cause of such diseases in the light of current medical knowledge. Accordingly, the current standards for the recognition can also be considered reasonable.

3. Risk Factors causing Cerebro-Cardio Diseases  

Risk factors such as hypertension, hyperlipemia, and/or smoking are affecting the appearance of cerebro-cardio diseases, and those who have multiple factors are subject to a higher risk of the diseases. As such, it is necessary to adequately understand worker health conditions, to fully examine the extent of underlying diseases and of heavy work burdens, and to make comprehensive judgments on the corelation between these factors and cerebro-cardio diseases occurring in workers.   


Factors other than excessive overtime work

Work Mode

Viewpoints to Evaluate Burdens

Irregular working


Frequency and extent of changes in work schedule, advance notifications, extent of expectations and extent of changes in work contents.

Long working hours of restricted movements

Work contents, work intensity (ratio of actual working hours to waiting hours), rest time and naptime, resting and napping facilities (space, air-conditioning and noises, etc.).

Frequent business trips

Work contents at business trips, frequency of such trips (especially overseas trips involving time differences), transportation, traveling hours and conditions, need for hotel stays, hotel facilities, whether adequate resting time including sleeping time is secured, and whether recovery from fatigue during trips is possible on return.

Shift work and late-night work

Extent of changes in work shifts, period of time between shifts, and frequency of late-night work during shift work.

Working environment


Whether a worker feels pains in hands or legs or severe shivering due to work in cold environments, whether a worker has put on clothing for cold weather with appropriate heat-retention capabilities suitable to the work intensity and surrounding temperatures, whether a worker can warm up during a series of such work assignments, and whether a worker is alternatively exposed to excessively warm and cold temperatures or must frequently enter into and exit from locations with a substantial difference in temperatures.  


Whether the noise level exceeds 70~80dB, and the time and frequency of exposure to such noises.

Time differences

Whether a worker has to travel from one location to another with a time difference of five hours or more, and the amount of such differences and the frequency of exposure to such differences.

Work with mental stress

[Daily work subject to mental stress]

Work volume, length of time involved in such work, worker experience and adaptive capabilities, and support provided by the company

[Irregular work causing mental stress during the period of time close to the appearance of a disease]

Severity of such irregular work (accidents or disasters) and extent of the