Case Study II: Diet, Noise, and Hearing Loss
By: George Cook, Au.D., CCC-A
The room was cold, the examination table was cold, and the stethoscope was even colder. I was sitting with my shirt off and freezing. Wanting to get an early jump on the day, I had scheduled my two-year physical first thing in the morning. Soon the physician was informing me that my cholesterol and triglycerides levels were significantly higher and that I was going to have to try to control the problem by diet. Of course I was irritated. Over the years I had given up smoking and alcohol and had begun a regiment of exercise. Eating to me remains one of life’s greater pleasures. I resented the idea of anything affecting those pleasures still remaining. Yet, I knew it was serious. In the back of my mind was a memory of an older study showing that diet affected hearing.
What about high-fat vs. low fat-diets?
When I returned to my office I began a partial search of the literature. The study I was looking for was by Rosen, Olin, and Rosen in 1970 (1). Over a period of five years, this study in Finland investigated the relationship between coronary heart disease, high cholesterol levels, intake of saturated fats, and hearing loss. Patients between the ages of 40-59 years in two mental hospitals were evaluated. In one hospital, the usual high fat diet was continued and in the other, a low fat diet was instituted. After five years, the diets in the two hospitals were reversed for four years. In the hospital with the high fat diet, hearing loss and coronary heart disease increased. When the diets were reversed, the results showed the low fat diet reversed the hearing loss and incidence of coronary heart disease.
From Rosen, Olin and Rosen (1)
Do high blood lipid levels (hyperlipidemia) facilitate hearing loss?
The literature is mixed on the effects of blood lipid levels and hearing loss. Some studies (2) show that elevated cholesterol and triglycerides increase hearing loss in the high frequencies. Researchers indicate hyperlipidemia may have a role on the occurrence of sensorineural hearing (SNHL) loss.
The literature is mixed on the effects of cholesterol levels. In one study hearing thresholds (3) have been found to be surprisingly and significantly better in those with raised cholesterol levels. But low high-density lipoprotein cholesterol reportedly has a different consequence (4). It appears that low high-density lipoprotein cholesterol concentration is associated with hearing loss but high cholesterol levels are not.
How about hypertension, noise and hearing loss?
It is well documented that there is a relationship between increased hypertension and high level noise exposure hearing loss. It is also well established that hypertension is associated with a decrease in auditory acuity. The longer the noise exposure, the more significant are the changes in both the auditory and cardiovascular systems. Therefore, those individuals more predisposed to hypertension are most affected by noise. A high cholesterol and high triglyceride diet will predispose hypertensive animals to hearing loss in moderate chronic noise (5). The result is synergistic with loss in the higher frequencies. This means that without the noise the loss may not occur and that the amount of loss is greater than expected with either condition alone.
Can diet prevent or treat noise-induced hearing loss?
Animal studies at the University of Florida (6) showed that ears exposed to noise produced antioxidant enzymes. These antioxidants were important in making the ear resistant to further noise damage. Experiments showed that if increased antioxidants were available, the ear became more resistant to both steady state and intermittent noise.
The mechanism for the death of hair cells in the cochlea is necrosis or apoptosis. In necrosis, the hair cell is ruptured by direct trauma and it dies. In apoptosis, the hair cell swells two or three times it normal size over a period of four days. The proteins in the cell are disassembled resulting in a slower imploding death. Most of the damage occurs not at the time of insult, but over a period of four days immediately following the insult.
The protective reaction of the body is to increase the availability of antioxidant enzymes. When this happens swelling is reduced and a toughening phenomenon takes place.
These metabolic and histological studies on animals indicate that making increased levels of antioxidants to the ear through diet would prevent and/or treat noise induced hearing loss. Food supplements, vitamin E and foods high in antioxidants as prunes and raisins might be capable of protecting the ear from noise exposure.
At the NHCA Hearing Conservation Conference in February, 2003, a presentation from the DOD Spatial Orientation Center, Department of Navy (6) concerned oto-protectants (antioxidants). Using the same logic as Henderson (5) (in fact Donald Henderson, PhD, was a contributor), N-acetylcysteine (NAC) was studied as a food supplement to provide antioxidants to the ear to treat and/or prevent noise induced hearing loss. NAC was selected as the experimental drug as it is FDA approved, has excellent safety/side effects over decades. NAC has been shown to be safe in high doses (2-8 grams) over prolonged administration. It has been used clinically for over 30 years. It is inexpensive and can be found at food supplement stores.
From Kopke, R.NHCA Conference Presentation 2/2003
From Kopke, R.NHCA Conference Presentation 2/2003
NAC was determined to prevent hearing loss by substantially reducing outer hair cell damage. It was successful even if given shortly after the noise exposure. The results have been reproducible at U. Mich.; SUNY, Buffalo; Karolinska Inst, on initial human data.
Future clinical uses presented include prevention/treatment in the following areas:
- High noise exposure in the work place
- High noise training (as gunfire) exposure
- Noise and toxic chemical exposures
- Acute acoustic injury treatment
- Recreational noise
- Toxin-induced (chemotherapy) hearing loss
- Some types of genetic hearing loss
- Some types of age related loss
- Viral inner ear disease
The condition of the cardiovascular system can greatly affect hearing loss and can contribute to predisposing the ear synergistically to noise exposure. Conditions as hypertension, mild-to-moderately high cholesterol levels and high triglyceride levels are conditions that can to some extent be affected by diet. Foods high in antioxidants and low in saturated fats are known to be significantly friendly to the cardiovascular system. In addition, significant amounts of antioxidants as provided in the food supplement N-acetylcysteine (NAC) is proving to be important in the prevention/treatment of noise induced hearing loss.
- Rosen S, Olin P, Rosen HV: Dietary prevention of hearing loss. Acta Otolaryngol 70:242-247, 1970.
- Acik, KT, et al , The effect of hyperlipidemia on hearing function. Kulak Burun Bogaz Ihtis Derg 2002 Mar-Apr;9(2): 112-6
- Jones, NS; Davis A., A retrospective case-controlled study of 1490 consecutive patients presenting to a neuro-otology clinic to examine the relationship between blood lipid levels and sensorineural hearing loss. Clin Otolaryngol 2000 Dec; 25 (6): 511-7
- Suzuki K., Kaneko M., Murai K., Influence of serum lipids on auditory function. Laryngoscope 2000 Oct;110 (10 pt 1):1736-8 (ISSN:0023-852X)
- Pillsbury HC: Hypertension, hyperlipoproteinemia, chornic noise exposure: Is there synergism in cochlear pathology? Laryngoscope 96:1112-1137, October 1986.
- Henderson, D: Noise Induced Hearing Loss Part A; Part B, Video Tape Transcripts, University Florida, AuD Distance Learning Program, 2002.
- Kopke, R: Otoprotectants: the Role of Antioxidants. Proceeding of 28th NHCA Hearing Conservation Conference, Feb. 20-22, 2003, Dallas, TX.