Evidence for a dose-response relationship between occupational noise and blood pressure

In this study, we investigated the role of occupational noise exposure and blood pressure among workers at 2 plants. A noise-exposed plant (plant 1, > or = 89 dBA) and a less-noise-exposed plant (plant 2, < or = 83 dBA) were chosen. Exposure was based on department-wide average noise measures; on the basis of job location and adjusting for layoffs during their employment at the plant, a cumulative time-weighted average noise level was calculated for each worker. The study population comprised 329 males in plant 1 and 314 males in plant 2. Their ages ranged from 40 to 63 y (mean ages = 49.6 and 48.7, respectively), and they had worked at least 15 y at the plant. The clinical examination was administered prior to the workday and measured height, weight, pulse, and blood pressure. In addition, we noted medical and personal-habits histories, including alcohol intake and cigarette smoking patterns. We used a questionnaire to determine in-depth occupation, military history, noisy hobbies, and family history of hypertension. When individuals who took blood-pressure medication were removed from the analysis, t tests for differences in average blood pressure between plants showed a mean systolic blood pressure of 123.3 mm Hg in plant 1 versus 120.8 mm Hg in plant 2 (p = .06) and a mean diastolic blood pressure of 80.3 mm Hg versus 77.8 mm Hg in Plant 1 and 2, respectively (p = .014). On the basis of data from the combined plants, multivariate analysis revealed that age, body mass index, cumulative noise exposure, current use of blood pressure medications, and alcohol intake were significant predictors for systolic blood pressure. Cumulative noise exposure was a significant predictor of diastolic blood pressure in plant 1 but not in plant 2, possibly reflecting a threshold effect.