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Variation during the week in the incidence of acute myocardial infarction: increased risk for Japanese women on Saturdays
  1. K Kinjo1,
  2. H Sato1,
  3. H Sato1,
  4. I Shiotani1,
  5. T Kurotobi2,
  6. Y Ohnishi3,
  7. E Hishida1,
  8. D Nakatani1,
  9. H Mizuno1,
  10. Y Yamada4,
  11. S Fukui5,
  12. M Fukunami6,
  13. S Nanto7,
  14. Y Matsu-ura8,
  15. H Takeda9,
  16. M Hori1,
  17. on behalf of the Osaka Acute Coronary Insufficiency Study (OACIS) Group*
  1. 1Department of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, Suita, Japan
  2. 2Osaka Police Hospital, Osaka, Japan
  3. 3Laboratory for Cardiovascular Diseases, SNP Research Centre, The Institute of Physical and Chemical Research (RIKEN), Tokyo, Japan
  4. 4Osaka Rosai Hospital, Sakai, Japan
  5. 5Kashiwara City Hospital, Kashiwara, Japan
  6. 6Osaka Prefectural General Hospital, Osaka, Japan
  7. 7Kansai Rosai Hospital, Amagasaki, Japan
  8. 8Ishinkai Yao General Hospital, Yao, Japan
  9. 9Department of Medical Information Science, Osaka University Graduate School of Medicine, Suita, Japan
  1. Correspondence to:
    Dr Hiroshi Sato, Department of Internal Medicine and Therapeutics, Osaka University Graduate School of Medicine, 2-2, Yamadaoka, Suita, Osaka 565-0871, Japan;


Background: Variations in the incidence of acute myocardial infarction during the week may differ between and within communities, according to lifestyle.

Objective: To identify potential triggering factors for acute myocardial infarction by examining variations in incidence in the days of the week within the Osaka area of Japan.

Patients: Of 2511 consecutive patients in this region who were admitted to hospital for acute myocardial infarction between April 1998 and March 2001 and consented to take part, 2400 who had a definitely identified time of onset were enrolled.

Results: For this group as a whole, no significant difference in incidence was noted between days of the week. However, in subgroup analyses women were shown to have significant variation through the week, peaking on Saturday with a 39% increase in relative risk (p = 0.037); working subjects showed a peak on Monday, with a 26% increase in relative risk (p = 0.038). Stratified analyses showed that in working men there was a prominent Monday peak in the onset of infarction, with a 30% increase in relative risk (p = 0.022), while in working women, there was no significant variation through the week.

Conclusions: Earlier findings of a Monday peak linked to increased physical and mental occupational stress are confirmed. There is also an increase in uncertain risk factors on Saturdays for Japanese women, possibly involving a stressful weekend burden for women. Confirmation of this finding in other communities may help identify triggers of acute myocardial infarction and be useful in prevention.

  • acute myocardial infarction
  • weekly variation
  • occupational stress
  • Japanese women

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  • * A full list of participating centres and physicians is given in the appendix.