by Barry Keate
Presbycusis is the term used to describe hearing loss due to aging. It is not the result of noise exposure, ototoxic medications, or other causes of hearing loss, although those conditions can contribute to it. Presbycusis is the cumulative effect of aging on hearing. Typically it is a bilateral (both ears), high frequency hearing loss, gradually encroaching into the lower frequencies, associated with difficulty in speech discrimination and central auditory processing of information.
Deterioration in hearing has been found to start very early, from about 18 years of age. Even young adults lose the ability to hear very high frequencies above 15 or 16 KHz. About 30-35% of adults between 65 and 75 years have some degree of hearing loss in the speech frequencies, between 300 and 3400 Hz. Over 75 years, this increases to 40-50% of people.
Hearing loss of all types, including presbycusis, noise exposure, ototoxic medications and other disease conditions are the leading causes of tinnitus. Presbycusis affects men more than women and for many people it is accompanied by tinnitus. One study has found the incidence of tinnitus in those with presbycusis is 11%.1
Deterioration that is due to aging occurs throughout the auditory system from the hair cells of the cochlea to the auditory cortex in the temporal lobe of the brain. Four sites of aging have been identified and presbycusis can be divided into 4 types based on these sites.2 However, the development of presbycusis typically involves simultaneous changes at multiple sites.
1 – Sensory presbycusis: This refers to loss of sensory hair cells and supporting cells inside the cochlea. These changes correlate with a precipitous drop in the high frequency thresholds, which begins during and after middle age.
2 – Neural presbycusis: This is atrophy of nerve cells in the cochlea and central neural pathways to the auditory cortex. One estimate is that 2,100 neurons are lost every decade out of 35,000 total. This begins early in life and may be genetically predetermined. Effects are not noticeable until old age because significant hearing loss doesn’t occur until 90% of neurons are lost.
3 - Metabolic presbycusis: This involves atrophy of the stria vascularis, a part of the outer wall of the cochlea that consists of capillary and small blood vessel loops. The stria vascularis maintains the chemical and bioelectric balance and metabolic health of the cochlea. Atrophy of this membrane results in hearing loss represented by all frequencies because the entire cochlea is involved. This tends to occur in people aged 30-60 years.
4 – Mechanical, or conductive, presbycusis: This is a thickening and stiffening of the basilar membrane within the cochlea. This membrane separates two liquid filled tubes that run along the coil of the cochlea. This correlates with a gradually sloping high frequency hearing loss that is slowly progressive.
Factors responsible for presbycusis:
- Heredity may determine features like early aging of the cochlea and susceptibility of the cochlea to drug insults.
- Atherosclerosis diminishes blood flow to the cochlea, thereby reducing the oxygen supply.
- Dietary intake of saturated fats may accelerate atherosclerotic changes.
- Diabetes reduces blood supply to the cochlea.
- Noise trauma can hasten presbycusis.
- Smoking accentuates atherosclerotic changes, aggravating presbycusis.
- Hypertension causes reduction in the blood supply to the cochlea.
- Ototoxic medications hasten the process of presbycusis.
The incidence of presbycusis varies widely among different societies. A 1962 study of a remote tribe in the Sudan called the Mabaans revealed significantly less hearing loss in the elderly population than in similarly aged populations in urban societies.3 Whether this is due to the lack of chronic noise exposure in this tribe or to the lack of chronic diseases common in industrial societies (atherosclerosis, diabetes, etc.) is not known.
Several studies have shown treatment with antioxidants can help prevent or slow presbycusis. A study on an animal model of tinnitus showed a combination agent comprised of six antioxidants was able to slow hearing deterioration in laboratory mice.4
In the Health Professionals Follow-Up Study, begun in 1986, 26,273 male health professionals were analyzed for their intake levels of several vitamins, including folate.5 The study found that men over 60 whose intake of folate from food and supplements was among the highest 20% of participants had a 21% reduction in the risk of developing hearing loss compared with those in the lowest fifth.
Michael Seidman, MD, has conducted extensive research into the causes, prevention and treatment of presbycusis. In a May, 2000 study, published in the peer-reviewed journal Laryngoscope, Dr. Seidman posits that the mitochondrial clock theory of aging is the basis for presbycusis.6
About 98% of the body’s energy is produced in the mitochondria, known as the energy factory of the cells. The mitochondria burn fatty acids and produce the molecule adenosine triphosphate (ATP). This molecule is the energy the cell uses to perform its many functions. There are thousands of mitochondria in each cell and they have their own DNA, completely separate from the DNA found in the rest of the cell. Over the years mitochondrial DNA (mtDNA) is damaged by free radicals and the cells steadily decline in their ability to produce energy. This leads to aging, disease and eventually death.
Most of the causes of presbycusis, mentioned above, result in the reduction of blood flow to the cochlea. This leads to the formation of free radicals, also called Reactive Oxygen Metabolites (ROM), which directly affect inner ear tissues. ROM also damage mtDNA, resulting in the production of specific mtDNA deletions. These mtDNA deletions lead to mutation of the chromosomes, which are associated with both aging of the organism and presbycusis.
In order to prove this hypothesis, Dr. Seidman set out to experiment on laboratory rats. One hundred thirty rats were variously assigned to one of 6 treatment groups:
Group 1 – 30% caloric restriction, Group 2 - Vitamin E over-supplementation, Group 3 – Vitamin C over-supplementation, Group 4 – Melatonin treatment (melatonin is an antioxidant), Group 5 – Lazaroid treatment (an aminosteroid antioxidant), Group 6 – Placebo control.
Results indicated that the 30% caloric-restricted group maintained the most acute auditory sensitivities and the lowest quantity of mtDNA deletions and the least amount of hair cells loss in the cochlea. The antioxidant treated animals had improved auditory sensitivities and fewer mtDNA deletions compared to the control group. The placebo animals had the poorest auditory sensitivity, the most mtDNA deletions and the greatest degree of hair cell loss.
Based on the above study, and many more during the last decade, Dr. Seidman has now developed the first all-natural treatment plan to battle hearing loss safely and effectively and can be found in his book, Save Your Hearing Now.
Dr. Seidman also developed the Antioxidant Formula, which will help fight free radical damage to the mitochondria.
- Podoshin L, Ben-David J, Teszler CB. Pediatric and geriatric tinnitus. Int Tinnitus J. 1997;3(2):101-103.
- Gacek RR, Schuknecht HF. Pathology of presbycusis. Int Audiol. 1969;8:199.
- Bergman M, Hearing in the Mabaans: A critical review of related literature. Arch Otolaryngol. 1966;84(4):411-415.
- Heman-Ackah S, Juhn S, Huang T, Wiedmann T. A combination antioxidant therapy prevents age-related hearing loss in C57Bl/6 mice. Otolaryngology-Head and Neck Surgery (2010) 143, 429-434.
- Shargorodsky J, Curhan SG, Eavey R, Curhan GC. A prospective study of vitamin intake and the risk of hearing loss in men. Otolaryngology-Head and Neck Surgery. 2010 Feb;142(2):231-6.
- Seidman MD. Effects of dietary restriction and antioxidants on presbycusis. Laryngoscope 2000 May; 110 (5Pt 1): 727-38.