Does influence at work modify the relation between high occupational physical activity and risk of heart disease in women?

PURPOSE: To investigate whether influence at work modifies the association between demanding and strenuous occupational physical activity (OPA) and risk of ischaemic heart disease (IHD). METHODS: A sample of 12,093 nurses aged 45-64 years from the Danish Nurse Cohort Study was followed for 20.6 years by individual linkage to incident IHD in the Danish National Patient Registry. Information on OPA, influence at work, other occupational factors and known risk factors for IHD was collected by self-report in 1993. RESULTS: During follow-up 869 nurses were hospitalised with incident IHD. Nurses exposed to strenuous OPA and low influence at work had a 46% increased risk of IHD [hazard ratio (HR) 1.46 (95% confidence interval (CI) 1.02-2.09)] compared to the reference group of nurses with moderate OPA and high influence at work. Nurses exposed to strenuous OPA and high influence at work were not at an increased risk of IHD [HR 1.10 (95% CI 0.59-2.06)]. An additive hazards model showed there were 18.0 (95% CI -0.01 to 36.0) additional cases of IHD per 10,000 person years among nurses with strenuous OPA and low influence at work compared to nurses with moderate OPA and high influence at work. A detrimental additive interaction between strenuous OPA and low influence at work that could explain the additional cases of IHD among nurses with strenuous OPA and low influence at work was indicated. CONCLUSION: The findings suggest that high influence at work may buffer some of the adverse effects of strenuous OPA on risk of IHD.