Abstract:
The interaction between age and noise and their individual effects on hearing is
complex, making it difficult to distinguish between noise-induced hearing loss and agerelated
hearing loss at an individual level. This retrospective cohort study aimed to
determine the decline in hearing sensitivity in noise-exposed mineworkers as opposed
to non-noise-exposed mineworkers over time to evaluate the combined and individual
contributions of noise exposure and age.
A mixed effects regression analysis was applied to longitudinal audiological data from
a group of mineworkers in South Africa. Four serial (annual) audiograms of 2,583
mineworkers were utilised. Data of a non-noise-exposed group (n=951) and a group
exposed to underground noise (≥85 dBA) (n=1632) were included.
Results indicated that base values were significantly higher for the noise-exposed
versus non-noise-exposed group, for the low-frequency average (LFA) of 0.5, 1 and 2
KHz (16.1 dB HL versus 11.1 dB HL), and high-frequency average (HFA) of 3, 4 and
6 KHz (25.7 dB HL versus 18.5 dB HL). These results may be indicative of previous
noise damage in the noise-exposed group obtained before occupational noise
limitations and personal hearing protection use were enforced through legislation in
2001. All year-to-year increases in mean hearing thresholds were statistically
significant (p-values of <0.01). When correcting for age, year-to-year increases in
mean hearing thresholds were higher for the noise-exposed group than for the nonnoise-
exposed group when comparing HFA (3.5 dB versus 2.9 dB decline over a fouryear
period) but similar when comparing LFA (0.6 dB versus 0.7dB decline over a fouryear
period). Mixed effects regression analyses were repeated without correcting for
age to represent year-to-year increases in hearing thresholds including noise and age
influences. Year-to-year increases in mean hearing thresholds were significantly
higher for the noise-exposed group than for the non-noise-exposed group in
comparing HFA (4.0 dB versus 3.5 dB decline over a four-year period), and when
comparing LFA (1.5 dB versus 1.1 dB decline over a four-year period). Year-to-year
increases in mean hearing thresholds were between 0.4 and 0.9 dB higher in the
analysis where age was uncorrected for, for both exposure groups across LFA and
HFA, identifying age as a factor in year-to-year decrease in mean hearing thresholds. It is evident that occupational noise exposure and aging are significant contributors to
hearing loss over time for mineworkers, even in a setting where noise exposure is
controlled through legislation, and use of personal hearing protection is enforced.
Ongoing effort is necessary to increase the effectiveness of noise management
programmes in order to counter the prevailing negative effects of noise exposure on
hearing thresholds, as well as the possible additive interaction between noise
exposure and age-related hearing loss.
