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Exposure to occupational noise and risk of cardiovascular disease : a retrospective cohort study Davies, Hugh William


Introduction: Noise is a powerful stressor that consistently produces physiological responses typical of a stress reaction in experimental settings. However, results of observational studies of a hypothesized link between noise and cardiovascular disease have been inconsistent. This retrospective study examined associations between occupational noise exposure and cardiovascular mortality in a pre-existing cohort of 27,499 lumber mill workers. Methods: Subjects were males from 14 lumber mills employed at least one year between 1950 and 1995. Historical exposure levels were estimated by a determinants-of-exposure regression model, developed using 1,900 personal dosimetry measurements. An exposure data matrix was created for 3,809 mill/job-title/time period combinations, then combined with work histories to calculate various cumulative exposure metrics. SMR's were calculated using the regional general population as referents. Exposure-response relationships were examined using Poisson regression, adjusted for age, calendar year and ethnicity. Results: There were 2,519 circulatory disease deaths, of which 910 were due to acute MI. SMR's for circulatory diseases were close to 1, although lower risks were anticipated due to the "healthy worker" effect. SMR's for acute MI were elevated 30-40% for workers exposed more than 30 years over 95 dBA, or for 20 years over 100 dBA. Within the cohort, relative risk (RR) of acute MI was increased 30-60% for those exposed more than 30 years over 95 dBA. To reduce exposure misclassification resulting from hearing protector use, a sub-cohort who terminated cohort employment before 1970 was created. Sub-cohort RR's for those exposed more than 20 years above 85, 90, and 95 dBA ranged from 1.3-1.5 (Ptrend's, <0.05). RR's for cumulative exposure reached 1.6 in the highest exposure group (>115 dBA*yr, Ptrend <0.001). RR's were greatest when follow-up was limited to the period of employment, ranging from 2-A (Ptrend's <0.01). RR's for ischemic heart disease were elevated but not as strongly or consistently as for acute MI. RR's for stroke and hypertensive diseases did not show consistent patterns of increased risk. Smoking did not appear to be a confounder. Conclusion: Occupational exposure to noise above 85 dBA is associated with increased risk of acute MI. Risks appear highest for those actively employed.

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