Incidence and risk factors for stroke in an occupational cohort -: The PROCAM Study

Background and Purpose-The purpose of this study was to assess the incidence of stroke and the magnitude of classic stroke risk factors in an occupational cohort of white-collar and blue-collar workers. Methods-We studied a prospective cohort of 12 866 male employees, aged 30 to 65 years, in 52 companies in northwestern Germany, with an average follow-up of 7.2 years. Participants were free of self-reported stroke, transient ischemic attack, and myocardial infarction at baseline. Physical examination, blood tests, and a face-to-face interview to assess presence of various risk factors were performed at the workplace. Follow-up was done by standardized mailed questionnaire. Main outcome measure was first stroke occurrence. Results-Overall stroke incidence was 42.4 per 100 000 person-years, increasing from 10.1 per 100 000 person-years in the age category 30 to 39 years to 33.6, 80.6, and 159.2 per 100 000 person-years in the age categories 40 to 49, 50 to 59, and 60 years and older, respectively. After adjustment for potential confounders, the relative risks of total stroke associated with systolic blood pressure less than or equal to 120, 121 to 140, and greater than or equal to 141 mmHg were 1.00 (reference), 2.99 (95% confidence interval, 0.85 to 10.49), and 5.56 (1.56 to 19.88). The risks associated with smoking status of never/past, less than or equal to 20 cigarettes per day, and >20 cigarettes per day) were 1.00 (reference), 1.65 (0.62 to 4.42), and 3.56 (1.78 to 7.15), respectively. A history of hypertension at baseline (yes versus no) was independently associated with a relative risk of 2.37 (1.20 to 4.71) for total stroke and a history of diabetes mellitus (yes versus no) with a risk of 2.21 (1.00 to 4.87). A comparison of risk factor levels with a general population study revealed only small differences. Conclusions-This occupational cohort had a 2-fold lower stroke incidence than that observed in cohorts of the general population. In the absence of a strong healthy-worker effect, moderate differences in behavioral risk factors and a higher treatment rate for hypertension contribute to the explanation of this favorable stroke incidence.