A longitudinal study of hearing level aggravation due to aging

Abstract

It has been reported that hearing aggravation due to aging is predominantly in the high frequency range and that there are rapid and slow phase of aggravation in hearing level. In the present study, the pattern of aggravation of hearing level due to aging was investigated in 387 adults of over 35 years of age who had visited the Kitasato Health Science Center for a regular health check-up annually for more than 5 years, and were diagnosed as having neither external of middle ear diseases nor hearing impairment of obvious origin at their first visit. The subjects were divided into 8 groups according to their ages in increments of 5 years. Their audiograms were obtained annually, and the results were used to obtain the distribution of the hearing level at each test frequency. All of the subjects were examined for individual changes in audiograms and those who showed 20 dB or more aggravation of hearing in a 1-year period without subsequent improvement were defined as having a rapid phase of aggravation. There were clustering points in hearing distribution at around 30 dB and 60 dB at the test frequency of 8 kHz in those subjects showing a rapid phase of aggravation. Similar clustering points were also noted in those subjects who showed gradual aggravation of 20 dB or more in a 5-year period and who had 20 dB or more aggravation in one year but showed later improvement. As for the test frequencies lower than 4 kHz, there appeared to be a clustering point at around 30 dB. The incidence of the rapid phase of aggravation was then determined in each group, in order to investigate the relationship between aging and the appearance of the rapid phase of aggravation. The rapid phase was already noted in the youngest age group (range, 35-39 years), while the incidence gradually increased up to the 50-54-year group and stayed at a constant level in the 55-69-year groups. The incidence markedly decreased thereafter. The results suggest that hearing aggravation due to aging does not occur at any particular age. Rather, the hearing aggravation appeared to be closely related to the hearing level, and to manifest itself when the hearing level approaches 30 dB or 60 dB.