Hypertension in noise-exposed sawmill workers: a cohort study

Objective: To investigate the hypothesised association between exposure to high levels of noise and risk of hypertension using quantitative exposure assessment and administrative health data. Methods: This study followed a cohort of 10 872 sawmill workers in British Columbia from 1991 to 1998. Subjects were linked with provincial hospital discharge, outpatient and vital status databases. Cases were males who died, had at least one hospital admission, or who had three doctor visits within 70 days, for hypertension (ICD-9 codes 401-405). We used four exposure metrics: cumulative exposure, and duration of exposure above thresholds of 85 dBA, 90 dBA and 95 dBA. Relative risks were estimated using Poisson regression with the low-exposure group as controls and adjusting for age, ethnicity and calendar period. Results: 828 cases were identified. The results showed a monotonic increase in hypertension incidence with cumulative exposure. The risk in the highest exposed population was 32% higher than baseline. Similar results were found using duration of exposure metrics. The highest relative risk was 1.5 in workers exposed for more than 30 years at 85 dBA. Exposure-response trends were statistically significant. Conclusions: The risk of hypertension was positively associated with noise exposure above 85 dB.