Risk factors for hearing loss across occupations

A survey in Norway has investigated the link between a worker’s job and the possible risk of hearing loss. While occupation was a factor in 2%–3% of the variance in hearing loss among men aged 45, it was of significance for less than 1% of women and young men. The most serious hearing problems in men were found among woodworkers, miners, electrical power line workers and cable jointers, carpenters, seamen and mechanics. Among women, there were only a few occupational groups indicating hearing problems.

Prevalence of hearing loss

Hearing loss is one of the most common health problems in the industrialised world (Davis, 1997). The World Health Organization (WHO) regards adult-onset hearing loss as the 15th most serious health problem. The European Union recognises noise-induced hearing loss as one of the most prominent occupational diseases (European Agency for Safety and Health at Work, 2002, 2005).

About 16% of disabling hearing loss worldwide can be attributed to exposure to noise in the workplace. Other risk factors for hearing loss include whole body vibration, work-related diseases and exposure to toxins (WHO, 2002).

A recent paper (Engdahl and Tambs, 2010) analysed data from a study on hearing loss in the Norwegian region of Nord-Trøndelag together with information from the nationwide occupation register compiled by the government agency Statistics Norway (SSB). The primary aim was to determine the effects of specific types of occupation on hearing loss.

About the survey

The Nord-Trøndelag hearing loss study is a part of the Nord-Trøndelag longitudinal population health study (HUNT). The entire adult population of the Norwegian county of Nord-Trøndelag County was invited to participate. The survey was conducted from January 1996 to February 1998 and included pure-tone audiometry and two questionnaires as part of the screening programme. In pure-tone audiometry, hearing is measured over a range of pure tones in each ear. Frequencies vary from low pitches (250 Hz) to high pitches (8,000 Hz).

A total of 51,574 people had their hearing tested and provided written informed consent. The subjects ranged in age from 20 to 101 years, and had a median age of 49. The participation rates varied from around 40% for people aged under 30 or over 80, to 82% for those aged between 60 and 69.

Information relating to occupation and education was obtained through a link with the population register information from SSB. The total sample consisted of 49,948 people with complete data.

Main results

The results showed that occupation had greater effects on thresholds averaged at 3,000–4,000 Hz than those averaged at 500–4,000 Hz.

The effect of occupation on hearing loss was also seen to be much greater in older people, with the most obvious explanation being a cumulative effect of exposure to noise. While age accounted for 6%–24% of the variance, occupation additionally explained 2%–3% of the variance among men aged under 45 and less than 1% of the variance among young men and women of all ages.

For men, self-reported occupational noise explained up to 2.2% of the variance over and above occupation type. The occupations with the highest hearing thresholds were woodworking and mining, with about 11 dB elevated thresholds at 3,000–6,000 Hz compared to the reference group.

Elevated hearing thresholds were also found among electrical power line workers and cable jointers, construction workers and carpenters, seamen, and workshop mechanics, for whom the magnitude of the hearing threshold elevation ranged from 7 to 10 dB at 3,000–6,000Hz.

The results also showed that occupation in general had greater effects on thresholds averaged at 3,000–4,000 Hz than those averaged at 500–4,000 Hz. Among women, there were only a few occupational groups with significantly elevated hearing thresholds, but the study does not specify what these occupations were.

Commentary

The strength of this study is that the complete occupation data for all participants, together with a relatively high participation rate in the population survey (67% for the vast majority of the county), makes a substantial selection bias unlikely. The biggest weakness of the study is the lack of information about length of employment or duration of exposure. Although only a moderate association between occupation and hearing loss was found in this study, unbiased estimates of occupational hearing loss may help identify high-risk occupations where interventions are needed.

References

Davis, A.C. (1997), ‘Epidemiology of hearing disorders’, in Kerr, A.G. (ed.), Scott Brown’s Otolaryngology, Butterworth-Heineman, Boston.

EU-OSHA (European Agency for Safety and Health at Work) (2002), Data to describe the link between OSH and employability, Publications Office of the European Union, Luxembourg.

EU-OSHA (European Agency for Safety and Health at Work) (2005), Noise in figures, Publications Office of the European Union, Luxembourg.

WHO (World Health Organization) (2002), The world health report: Reducing risks, promoting healthy life, Geneva.

Engdahl, B. and Tambs, K. (2010), ʻOccupation and the risk of hearing impairment – results from the Nord-Trøndelag study on hearing loss᾿, Scandinavian Journal of Work and Environmental Health, Vol. 36, No.3, pp. 250–257.

Bjørn Tore Langeland, National Institute of Occupational Health

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