Monday, January 24, 2005

Noise Kills

Occupational exposure to noise causes hearing loss. Ear plugs and muffs don’t sufficiently protect, so that hearing conservation programs [noise measurements, HPD’s and audiograms] primarily measure workers going deaf [maybe more slowly than without the program. Nevertheless, progress on controlling occupational exposure to noise stalls because going deaf isn’t enough of a health effect to induce management to install expensive engineering controls, or even maintain what’s there already. Recent reviews – which BrooklynDodger will post on another day – find that noise exposure causes high blood pressure. High blood pressure in turn causes cardiovascular disease and death. So, noise kills.

The paper sited below provides clear evidence for noise exposure related cardiovacular mortality.

The investigators identified over 27,000 blue-collar workers from lumber mills in British Columbia. Cumulative noise exposure was quantitatively assessed. During the follow-up period, 2510 circulatory disease deaths occurred. Relative risks for acute myocardial infarction mortality were elevated in the full cohort, with a stronger association in the subgroup without hearing protection. There was an exposure-response trend, with a relative risk in the highest exposed group of 1.5. The highest relative risks (2.0-4.0) were observed during subjects' working years. Smoking did not appear to confound these associations. The investigators concluded that chronic exposure to noise levels typical of many workplaces was associated with excess risk for acute myocardial infarction death.

BrooklynDodger points out that the Healthy Worker Effect (HWE) is a huge obstacle to detecting employment related effects on all cause mortality or cardiovascular mortality. In this case, the investigators were able to observe an exposure response trend within the population, which is often the most difficult part of an epidemiologic study.

Making the case for spending money to control noise depends mostly on connecting the dots from diverse studies. Noise causes hearing loss. Hearing protectors don’t work – showing that workers using hearing protectors are exposed to noise. Noise exposure causes high blood pressure. High blood pressure causes cardiovascular disease. However, this study connects the dots.

Epidemiology. 2005 Jan;16(1):25-32.

Occupational exposure to noise and mortality from acute myocardial infarction.

Davies HW, Teschke K, Kennedy SM, Hodgson MR, Hertzman C, Demers PA.

School of Occupational and Environmental Hygiene, University of British Columbia, Vancouver, British Columbia, Canada.

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