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Many investigators who have analysed the possible correlation between hearing loss and high serum cholesterol levels have found that hearing appears to be influenced by high blood lipids. Noise, as is well known, also influences hearing, particularly at high frequencies. It increases serum cholesterol levels during short-term experiments. The present investigation addresses the question of a possibly increased ototraumatic influence by the combination of high serum cholesterol levels and occupational noise exposure. Seventy-eight 50-year-old men with high serum cholesterol levels from a WHO study were compared with 75 50-year-old men who were randomly selected from the same WHO material. Group mean audiograms showed that hearing was similar in both groups, with a moderate high frequency hearing loss having a configuration suggestive of a noise-induced hearing loss. Analysis of the individual histories and the pure-tone audiograms showed that noise was the most predominant factor influencing hearing at any specific frequency or combination of frequencies. There was a statistically significant tendency for the high-cholesterol group that had suffered the most noise exposure, to have a high-frequency hearing loss. There was also a tendency for the low-cholesterol group to have a high-frequency loss if they had been excessively exposed to occupational noise. No further correlations were found. The present results indicate a slightly increased risk of acquiring a high-frequency sensorineural hearing loss for people who work in noisy environments and have high serum cholesterol levels.

A hearing examination of 538 teenage boys in vocational school classes--implying future on-the-job noise exposure--showed a hearing loss (greater than 20 dB HL at any frequency) in 15% of the cases. Few correlations could be demonstrated between hearing loss and specific leisure time activities. There was, however, a correlation between high frequency hearing loss in the left ear and hereditary hearing loss. The most affected frequency was 6 kHz, suggesting a noise etiology--a suggestion emphasized by the noisy hobbies of these teenagers. It cannot be excluded that a hereditary deficiency could either manifest itself as a localized dip at 6 kHz or reveal itself as an increased vulnerability to noise, identified at young age as a high frequency dip at 6 kHz.

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