Written by Greg Arnold, DC, CSCS. In a study, 53 workers exposed to high noise were given 1200 mg NAC or a placebo. Those in the NAC group were able to hear at 21.7 decibels compared to 22.1 in the control group.
An estimated 10-15 million Americans have noise-induced hearing loss, with 16% of the disabling hearing loss in adults worldwide being due to excessive exposure to noise in the workplace (1). According to the National Institutes of Health, repeated exposure to sounds at or above 85 decibels can cause hearing loss. The most severe loss occurs from 120 to 150 decibels (motorcycles, firecrackers, and small firearms). The humming of a refrigerator is 45 decibels, normal conversation is approximately 60 decibels, and the noise from heavy city traffic can reach 85 decibels (2).
Research has shown that noise-induced hearing loss causes free radical cell damage that contributes to the structural damage in the inner ear from the exposure to high decibel levels (3). As a result, ways to help scavenge those free radicals may help maintain hearing. Now research (4) suggests N-Acetyl Cysteine may be of benefit.
In the study, 53 male workers at a steel manufacturing plant who had daily exposure to at least 90 decibels per day for an average of 16.3 years received either 1200 mg/day of N-Acetyl Cysteine or placebo for 14 days. This was followed by a 2-week “washout” period and then another 14 days during which the supplementation was switched. Each patient provided blood samples and underwent hearing examinations before and after the study.
By the end of the study, N-Acetyl cysteine helped maintain hearing after noise exposure significantly better than placebo. Specifically, workers were able to detect high-frequency noises at an average of 19.3 decibels before the workers started their shift. After their shift, they were tested again and the N-Acetyl Cysteine group was able to hear high-frequency noises at an average of 21.75 decibels (a 2.44-decibel shift) compared to 22.07 decibels (a 2.77-decibel shift) in the placebo group (p = 0.03), representing a 12% average smaller decibel shift after noise exposure.
An interesting finding in the study was that those with a certain genotype called “GSTM1-null and GSTT1-null” (“null/null”) experienced significant benefits from N-Acetyl Cysteine supplementation. While the entire N-Acetyl Cysteine group had a 2.45-decibel threshold shift after noise exposure, those with the “null/null” genotype had only a 1.2-decibel shift, representing a 51% smaller decibel threshold shift after noise exposure (p = 0.004).
For the researchers, “N-Acetyl Cysteine may prevent noise-induced [temporary threshold shift] among occupationally noise-exposed men” and that “The protective effect of N-Acetyl Cysteine was more prominent in subjects with both GSTM1-null and GSTT1-null genotypes.”
Source: Lin, Cheng-Yu, et al. “N-Acetyl-cysteine against noise-induced temporary threshold shift in male workers.” Hearing research 269.1 (2010): 42-47.
© 2010 Elsevier B.V. All rights reserved.
Posted November 30, 2012.
Greg Arnold is a Chiropractic Physician practicing in Hauppauge, NY. You can contact Dr. Arnold directly by emailing him at PitchingDoc@msn.com or visiting his web site at www.PitchingDoc.com
References:
- Nelson DI. The global burden of occupational noise-induced hearing loss. Am. J. Ind. Med. 2205; 48 (6):446-458.
- “Noise-induced hearing loss” posted on the National Institutes of Health’s National Institute on Deafness and Other Communication Disorders.
- Clerici WJ. Direct effects of intraperilymphatic reactive oxygen species generation on cochlear function. Hear. Res. 1996; 101 (1-2);14-22.
- Lin CY. N-Acetyl-cysteine against noise induced temporary threshold shift in male workers. Hear Res 2010;269(1-2):42-7.
