A five-year longitudinal study of hearing in a Danish rural population aged 31-50 years.

This paper aims to report changes in hearing sensitivity over five years in a rural population aged 31-50 years and to identify risk factors associated with hearing deterioration. The study is prospective and based on data from pure tone audiometry and questionnaires in the Ebeltoft Health Promotion Project in Denmark. A representative sample of 705 subjects had a complete follow-up, including audiometry. The median hearing deterioration was 2.5 dB at 3-4 kHz and 0 dB at 0.5-2 kHz. There was a high degree of individual variability in deterioration. The overall deterioration of hearing sensitivity of the population was largely predicted from the cross-sectional findings reported previously. In the analysis of risk factors, hearing deterioration was defined as an average deterioration 10 dB/5 years at 3-4 kHz in at least one ear. Deterioration was present in 23.5% of the sample. The 41-50-year-olds had a relative risk of deterioration of 1.32 (95% CI 1.01-1.73) compared with the 31-40-year-olds. Males had a relative risk of 1.35 (1.03-1.76) compared with females. The risk was not significantly elevated for a range of other possible risk factors confirmed by logistic regression analysis. In conclusion, deterioration in hearing sensitivity on population level can be predicted on the basis of cross-sectional findings. Hearing sensitivity deteriorated mainly at 3-4 kHz. The deterioration increased with age and was higher in males than in females. Other risk factors were not found. The present study does not support the hypothesis that hypertension or tobacco smoking is associated with deterioration in hearing.