Prolonged exposure to industrial noise causes hearing loss but not high blood pressure: a study of 2124 factory laborers in Japan.

To determine the role of noise exposure in the etiology of hypertension, a cross-sectional study was performed by measuring the blood pressure of 2124 male laborers working in a noisy factory. The prevalence of hypertension was 10.2% in group I (85-115 dB), 10.9% in group II (less than 85 dB) and 12.5% in group III (office workers). There was no difference in systolic or diastolic blood pressure among the three groups. There were 358, 439 and 71 laborers in groups I, II and III, respectively, all having worked in the same noise area for more than 10 years. Blood pressure was lower 10 years previously in each group, but the degree of increment did not significantly differ among the three groups. The prevalence of hearing loss was 16.5% in group I, which was significantly higher than that in group II (7.5%) and group III (2.8%). Blood pressure of laborers with hearing loss was equal to that of laborers with intact hearing acuity. There was no significant relationship between hearing loss and the prevalence of hypertension. Thus, prolonged exposure to industrial noise contributes to hearing loss. However, elevation of blood pressure was not found in laborers working in a noisy factory. This finding was not consistant with previously reported findings in the rat. An adaptability to prolonged noise in man may account for this discrepancy.