Introduction

Noise is an environmental pollutant, and occupational noise is a potential hazard to the hearing of exposed workers. The damaging effect of noise on hearing ability has been demonstrated in experimental and environmental studies. Less-well researched is the possible effect of environmental noise on other body systems - e.g. the cardiovascular system. Its role as a risk factor for hypertension has been proposed frequently over the last twenty years, but good evidence has so far been lacking. Recently, however, a group of Polish scientists have published the results of a study in steelworkers exposed to different levels of occupational noise.

What was done

A randomly-selected group of workers in a metallurgical plant in Poland were examined by audiometry testing, and by measuring height, weight, and blood pressure; they also completed a questionnaire. All examinations were done at the same time of day, before the work shift.

The questionnaire provided information about the worker's job and home environment, his perception of work noise, use of hearing protectors, exposure to noise outside the workplace, cardiovascular history, usual diet, and use of tobacco and alcohol.

The actual exposure to noise was determined for each participant's place of work by direct or indirect measurements of noise levels.

What was found

There were 302 workers under 35 in the original list of participants. However, individuals who had been working for less than three years in their present job as well as those with a history of high blood pressure or the use of medication for cardiovascular disease were eliminated, leaving information from 178 workers for analysis.

Average values were: age 28; years in the workforce 7; Body Mass Index (BMI) 24.1; and blood pressure 122/80 mm Hg. Physical exertion at work was reported by 79%. Perception of noise at work was 'sometimes' in 58%, and 'always' in 33%. Almost all of them (98.5%) used ear protectors.

The average noise level at their place of work was 84.3 decibels. Compared with this average level, there were 104 workers who had a greater exposure ("high"), and 75 who had a lesser exposure to noise ("low"). The "high" exposure workers had significantly increased systolic blood pressure levels, compared with the "low" exposure men - averages of 125 mm Hg vs. 121 mm Hg. Average diastolic pressures were the same in both groups - 80 mm Hg.

The only other significant effect on blood pressure was the BMI level. Values below 25 were associated with lower average diastolic blood pressure (as might be expected). Audiometry tests were within normal limits in all cases, and there were no differences in results according to noise exposure.

What these results mean

The findings show that chronic occupational exposure to noise significantly influences the systolic blood pressure. This was confirmed by a statistical procedure called 'multiple regression analysis', where possible influences of the other measured factors on the findings were eliminated, one after the other.

It's interesting to note that almost all the workers used ear protectors, while there were no abnormal audiometry results; this indicates the effectiveness of ear protectors in safeguarding hearing. Other researchers, however, have suggested that effects of noise on blood pressure become apparent earlier than those on hearing; it's possible that the years at work in this study were not long enough for an effect on hearing to manifest itself.

Although the average differences in systolic pressure between those exposed to noise at high and low levels were quite small, any increase in systolic pressure that can be eliminated is important. Workplaces should be made as quiet as reasonably possible, both for the benefit of workers and for those living or passing nearby.