Long working hours and risk of hypertensive intracerebral haemorrhage among Japanese workers claiming compensation for overwork-related intracerebral haemorrhage: an unmatched case–control study

OBJECTIVES: Overwork-related cerebrovascular and cardiovascular diseases (CCVDs) constitute a major occupational and public health issue worldwide. However, to our knowledge, few studies have reported the underlying pathophysiological mechanisms. We aimed to determine whether patients with extreme workload have a greater risk of developing hypertensive intracerebral haemorrhage (ICH) located in the deep brain areas than patients without extreme workload. We also determined the association between the number of hours of overtime work and the risk of developing hypertensive ICH. DESIGN: Unmatched case–control study. SETTING: Database of patients claiming compensation for overwork-related CCVDs in Japan. PARTICIPANTS: A total of 1215 patients who claimed overwork-related ICH in Japan, of whom 621 had their compensation claim approved (patients with extreme workload) and 622 did not. PRIMARY AND SECONDARY OUTCOME MEASURES: Logistic regression analysis was performed to calculate the risk of developing hypertensive ICH in patients with extreme workload compared with those without extreme workload, adjusted for confounders such as age, occupation, smoking status, alcohol consumption and medical history. We also calculated the risk of developing hypertensive ICH in compensated patients by average monthly overtime working hours. RESULTS: Patients with extreme workloads had a significantly higher odds ratio (OR) for developing hypertensive ICH (1.44, 95% CI: 1.10 to 1.88) than those without extreme workloads. ORs for developing hypertensive ICH according to overtime working hours showed a dose−response relationship; an overtime of 100 hours/month was associated with a significantly higher OR (1.31, 95% CI: 0.89 to 1.91; 1.41, 95% CI: 0.95 to 2.11; and 1.50, 95% CI: 1.01 to 2.22 for 60–79.9, 80–99.9 and≥100 hours/month, respectively) than that for workloads of less than 60 hours/month. CONCLUSIONS: Regarding Japanese workers, overtime work could be associated with the risk of developing hypertensive ICH, and hypertension may play an important role in overwork-related ICH.