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|Year : 2003 | Volume
| Issue : 20 | Page : 47--53
The influence of ageing on noise-induced hearing loss
Department of Clinical Neuroscience, Karolinska Institute/ Department of Audiology, Karolinska Hospital, Stockholm, Sweden
Hörselkliniken, Karolinska Sjukhuset, 171 76, Stockholm
A lifetime of exposure to noise is likely to have negative effects on the hearing, but the interaction between noise-induced hearing loss (NIHL) and age-related hearing loss is difficult to determine. The most commonly accepted assumption is a simple accumulating effects of noise and ageing on the hearing. However, both a less than additive effect as well as a supraadditive effect has been proposed. Recently an interesting interaction between NIHL and agerelated hearing loss has been reported (Gates et al., 2000). NIHL before old age reduces the effects of ageing at noise-associated frequencies, but accelerates the deterioration of hearing in adjacent frequencies. Findings from the longitudinal and cross-sectional gerontological and geriatric population study of 70-year-olds in Gothenburg, Sweden supports these observations. The incidence of tinnitus increases in old age, but not at the same high rate as presbyacusis. According to the gerontological and geriatric population study in Gothenburg tinnitus in old age is related more to hearing loss than to ageing. There are no simple correlations between exposure to noise during the active years and tinnitus in old age.
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Rosenhall U. The influence of ageing on noise-induced hearing loss.Noise Health 2003;5:47-53
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Rosenhall U. The influence of ageing on noise-induced hearing loss. Noise Health [serial online] 2003 [cited 2020 Jul 14 ];5:47-53
Available from: http://www.noiseandhealth.org/text.asp?2003/5/20/47/31689
Age-related hearing loss has a complex aetiology including both intrinsic and extrinsic factors. Among the latter factors the influence of noise exposure has since long been regarded to be of importance. An influence of noise on presbyacusis has been postulated in numerous reports for almost a century. However, it is difficult to identify one single factor, e.g. effects of prolonged noise exposure, with duration of many decades. The effect of noise is equivocal. The interactions between noise-induced hearing loss (NIHL) and age-related hearing loss are complex, difficult to determine, and poorly understood. One major problem is that agerelated hearing loss is extremely multifactorial.
Poorer pure tone thresholds have been found especially in noise-exposed elderly men than in those not exposed for occupational noise, but there is no unanimous consensus. Results from five different epidemiological investigations regarding pure tone thresholds from male populations aged 70-80 years are shown in [Figure 1]. In four of these investigations unscreened populations have been studied (Gates et al., 1990; Davis, 1995; Jonsson & Rosenhall, 1998; Cruickshanks, 1998). The results of these investigations were fairly similar ([Figure 1], thick, grey line). The fifth study comprised men screened for otological disease and noise exposure (the Baltimore Longitudinal Study of Aging, Pearson et al., 1995). The difference between the pure tone thresholds from the compiled material of unscreened populations and the screened population is striking. The screened population had better thresholds not only within the typical NIHL area (3-6 kHz), but over the entire frequency range. This indicates that not only exposure to noise, but also other confounding factors, are important. However, the situation is complicated. In Davis very large material from the MRC National Study of Hearing from the UK (Davis, 1995) the threshold differences between screened and unscreened populations are very minute.
Influence of noise on presbyacusis - Is there an increased or decreased sensitivity to noise with age?
The traditional model to assess NIHL in older persons assumes that presbyacusis adds to permanent noise-induced threshold shift (NIPTS). This additive model is embraced by ISO 1999, and is favoured by earlier literature (Welleschick & Raber, 1978). The formula suggested by ISO 1999 has the implication that the total hearing loss is the sum of age-related hearing loss and NIPTS minus a compression factor that is used when threshold shifts exceeds 20-25 dB.
However, this basically additive model has been challenged (Bies & Hansen, 1990; Macrae, 1991; Mills et al., 1996). A less than additive model means that the deterioration caused by presbyacusis is reduced within the noise frequencies in noise-damaged ears. Another implication is that noise injury is less likely in the aged ear with presbyacusis. Mills et al. (1998) exposed gerbils to intense short-term noise at young age. The animals were tested with ABR at old age. Their conclusion was that the additive model overestimates the interaction between noise and ageing. However, contradictory results have also been published. According to Henry (1982a,b) older mice without presbyacusis have a slightly increased susceptibility to noise overstimulation compared to young adult mice. Miller et al. (1998) studied different strains of mice (CBA/Ca and C57/BL/6) and found that ageing, with or without hearing loss, increased the sensitivity to NIHL. However, other factors like genetic disposition, might contribute to NIHL.
Gates et al. (2000) have described an interesting and intriguing finding in elderly men with noisenotches in their audiograms. In these subjects they found a reduced progress of hearing loss over time at 3, 4 and 6 kHz, and an accelerated hearing loss in frequency areas adjacent to noisedamaged frequencies, especially 2 kHz. In men without typical noise-notches this pattern was reversed. These data suggest that the ageing process is different in a noise-damaged cochlea than in a "pristine" one. The deterioration is less in the NIHL-frequencies in a noise-damaged ear than in an ear not influenced by noise, but increases in adjacent frequencies, corresponding to an increased vulnerability of the regions on the basilar membrane bordering to the NIHLregion.
Tinnitus and ageing
Tinnitus occurs in all age groups, and in most studies it increases, like hearing loss, with age. However, this increase with age is not as pronounced as the hearing decline related to age. According to Davis no or only little increase occurred in the total prevalence with increasing age. The total prevalence of tinnitus, both continuous and variable, has been reported at less than 20% to more than 40% in elderly people (Axelsson & Ringdahl, 1989; Davis, 1995). Severely annoying tinnitus was reported in 3-4%. The prevalence of tinnitus was similar between men and women in the studies cited.
Study design, study groups and methods
The longitudinal and cross-sectional gerontological and geriatric population study of 70-year-olds in Gothenburg, Sweden (H70) started in 1971. The aims of the study were to make a survey of the medical and social conditions in old age and to collect data for planning the care of elderly people. The study also intended to contribute to the knowledge of normal ageing processes and to provide normative geriatric data (3). The study includes an investigation of presbyacusis. Since retrospective knowledge of occupational noise exposure is available, it is possible to get information from this project concerning the interaction between age and noise.
The study comprises four age cohorts (cohorts 15). The study started with cohort 1 in 1971, and this cohort has been followed from age 70 to age 90 at seven occasions. The design was partly longitudinal. The original cohort was reduced by ailing health and decease with increasing age. From age 85 and onwards the cohort got an influx of participants from the same age group. Cohort 2 was studied twice, first at age 70 in 1976 and a second time five years later. Cohort 4 was studied at age 75 in 1990-91 and cohort 5 at age 70 in 1992-93. The participants were tested at 2352 occasions [Table 1]. Altogether 1485 subjects (869 women and 616 men) participated in the investigation.
All participants were tested with pure tone audiometry performed according to internationally accepted methods. They also responded to two questionnaires. One of these contained questions related to socio-economic questions e.g. occupation before retirement and exposure to occupational noise. The other contained questions related to hearing problems and tinnitus. For details see Rosenhall et al. (1990), Rosenhall & Karlsson 1991, and Jonsson and Rosenhall (1998),
Age-related hearing loss and occupational exposure to occupational noise
There was a pronounced difference in a crosssectional study between 70-year old men exposed to massive occupational noise, compared to a control group [Figure 2]. This difference was not confined only to the NIHLarea, but also at 1 and 2 kHz.
The most profound deterioration of the hearing between age 70 and age 75 was found at the frequency 2 kHz for both men exposed and not exposed to noise, but the deterioration was much more pronounced for the exposed group, the difference being more than 1 dB per year [Figure 3]. The deterioration was considerably less at the NIHL-frequency 4 kHz. The reduced deterioration was about the same for both groups at this frequency. The annual deterioration was much less for all frequencies with no apparent difference between the two groups between age 75 and 79.
In the group of 70-year-old men those reporting continuous tinnitus had a history of occupational noise exposure twice as often than those without this exposure. In the group without tinnitus the non-exposed group was larger than the noiseexposed group [Figure 4].
A striking finding was that the 70-year-old men with continuous tinnitus had elevated pure tone thresholds over the entire frequency range compared with those without tinnitus and also compared with those with occasional tinnitus [Figure 5].
Those 70-year-old men with a history of occupational noise exposure had poorer hearing than those without such an exposure, but the difference was not very pronounced. This was the case for the non-tinnitus group [Figure 6]a, but also to an even greater extent for the tinnitus group [Figure 6]b.
A review of the literature shows that the interaction between ageing and NIHL is complicated and even controversial. A basically additive model is favoured by ISO 1999. Mills et al. (1996, 1998) reported that a less-than additive model was in agreement with their findings in gerbils, and that the additive model overestimates the interaction between noise and ageing. In other animal studies an increased susceptibility to NIHL with increasing age has been reported (Henry, 1982a,b; Miller et al., 1998). In these cases other factors (e.g. genetic disposition) might contribute to NIHL.
Gates et al. (2000) have described a continued loss of hearing in individuals with noise-notches at frequencies adjacent to noise frequencies, especially at 2 kHz. This accelerated loss of hearing in noise exposed individuals was also accompanied by a decreased loss at the noise frequencies, compared with a contrast without noise notches. Data from the gerontological and geriatric population study of Gothenburg, Sweden, indicates that the age-related deterioration of the frequencies 1, 2 and 8 kHz is more pronounced in elderly men exposed to noise compared with those not exposed to noise from age 70 to age 75. This observation supports the report by Gates et al. (2000). However, the decline at the noise frequency 4 kHz was much less pronounced for both groups in the Gothenburg study. At a follow-up of part of the study group at age 79 the decline of hearing from age 75 to age 79 was much less pronounced over the entire frequency range and the same for both exposed and non-exposed men (Rosenhall et al., 1990). At age 79 the difference between exposed and not exposed subjects was considerably smaller. However, the design of the Gothenburg study was only partly longitudinal (the number of participants was larger at age 70 than at age 75). The material of the study will be reevaluated to provide a genuine longitudinal follow-up.
The incidence of tinnitus increases in old age, but not as much as age-related hearing loss.
It has been shown that elderly persons with tinnitus have poorer hearing than those without tinnitus (Axelsson & Ringdahl, 1989; Rosenhall & Karlsson, 1991). Tinnitus in old age is more strongly related to hearing loss than to age per se. For those men who reported continuous tinnitus, as well as for those who had no tinnitus, exposure to occupational noise was a determinant for hearing loss. However, the difference in hearing capacity between exposed and not exposed men was only minor and not only confined to the noise frequencies, which was especially noticeable in the tinnitus group. In the tinnitus group non-exposed men with hearing losses of other types than occupational NIHL obviously were common. One conclusion of the present study is that there is no simple correlation between exposure to noise during the active years and tinnitus in old age.
This study was supported by grants from: the Swedish Association of Hard of Hearing, Hjalmar Svensson Foundation, the Lions Foundation, the Swedish National Board of Health and Welfare, Wilhelm and Martina Lundgren's Foundation, the Gothenburg Medical Services Administration and Department of Geriatric Medicine, Sahlgrenska University Hospital, and Karolinska Institute, Stockholm, Sweden.
The manuscript is based on a lecture presented at the meeting "Individual susceptibility to noise damage", a NOPHER Conference (European Commission Concreted Action. Noise Pollution Health Effects Reduction). 19-20 July 2002. Novartis Foundation, London, UK
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