BACKGROUND: The combination of hypertension and high physical activity at work may increase blood pressure considerably and increase the risk of atherosclerosis and thereby ischaemic heart disease (IHD), but only a few studies in men, and none among women, have examined this topic.
DESIGN: This was a prospective cohort study.
METHODS: In 1993, 12,093 female nurses from the Danish Nurse Cohort Study, aged 45-64 years answered a baseline questionnaire on physical activity at work, history of hypertension, a selection of known risk factors for IHD and occupational factors. Information on incident IHD from baseline to 2008 was retrieved by individual linkage to the National Register of Hospital Discharges.
RESULTS: In a fully adjusted Cox model, hypertensive nurses with high physical activity at work had nearly three times higher risk of IHD (hazard ratio (HR) 2.87 (95% confidence interval (CI) 2.12-3.87)) compared to normotensive nurses with moderate physical activity at work. Significant additive interaction between physical activity at work and hypertension was found measured by the relative excess risk due to additive interaction (RERI) (1.20 (95% CI 0.26-2.14), and in an additive hazards model. Hypertensive nurses with high physical activity at work had 60 additional cases of IHD per 10,000 person years compared to normotensive nurses with moderate physical activity at work (60.0 (95% CI 38.1-81.9; p < 0.001)), of which more than half was explained by additive interaction (40.7 (95% CI 11.7-69.7; p = 0.006)). No multiplicative interaction (p = 0.249) was found.
CONCLUSIONS: This study among Danish nurses indicated that hypertensive women may be at particular high risk of IHD from physically demanding work.