IS NIDDM A RISK FACTOR FOR NOISE-INDUCED HEARING-LOSS IN AN OCCUPATIONALLY NOISE EXPOSED COHORT

Little is known about what factors, other than chronic exposure to noise, predispose individuals to noise-induced hearing loss (NIHL). The current retrospective study was designed to identify risk factors for NIHL in a population of 229 men [age 55-68 (mean = 63 years)] employed at a metal assembly plant. All men had been chronically occupationally noise-exposed for approximately 30 years (greater-than-or-equal-to 89 dBA) with an average E(a) noise emission level) of 104.5. The clinical examination included a pure-tone threshold audiometric evaluation, discrimination of speech in background noise [W-22 Max (> 60% indicating better hearing)], blood pressure measurement, evaluation of lifestyle (alcohol consumption, cigarette smoking, noisy hobbies) and occupational and military history. Severe NIHL was defined as greater-than-or-equal-to 65 db loss at 3, 4 or 6 kHz in at least one ear +/- 20 db threshold in the contralateral ear. History of non-insulin dependent diabetes mellitus (NIDDM) was reported by 16.4% of the 146 men with severe NIHL compared to 4.8% of the 83 men without severe NIHL (odds ratio = 3.9, C.I. 1.2-11.9, P = 0.05). Simultaneous evaluation of several potential risk factors using a multiple logistic regression indicates that the significant predictors of severe NIHL were diabetes (P < 0.05), E(a) (P < 0.05) and age (P < 0.05). These results suggest that a person with NIDDM who is also occupationally noise-exposed is more likely to develop severe NIHL than those without NIDDM. Longitudinal studies are necessary to confirm the temporal relationship between NIDDM and NIHL and to determine the exact mechanisms that are involved with this increased risk of hearing loss.