by Barry Keate
For years I have recommend the use of N-acetyl cysteine (NAC) to individuals with recent exposure to loud noise or ototoxic medications for protection against increased tinnitus and hearing loss. NAC must be taken either before or shortly after such exposures in order to be effective.
I have discussed some of the uses of NAC in an earlier article on antioxidants and brain calming supplements and have featured its benefits in numerous Ask Barry questions. Until now I have not outlined all the health and protective benefits of NAC in one paper.
NAC is a stable form of the sulfur containing amino acid cysteine. It is a powerful antioxidant and precursor to glutathione, the body’s primary antioxidant and free radical scavenger. There are many wonderful benefits of this supplement and we will discuss all of them. NAC is an inexpensive dietary supplement found in most health food stores.
Noise-Induced Hearing Loss and Tinnitus
Researchers have known for many years that high-level noise induces oxidative stress in the cochlea. It does this by causing a decrease in blood flow, releasing excessive amounts of glutamate, a toxic excitatory neurotransmitter, and stressing the mitochondria. Oxygen free radicals are thereby generated in the cochlea. Free radicals are toxic to the hair cells and neurons in the auditory pathway. (1)
NAC can be used by the body to make glutathione, the body’s own antioxidant defense. When a loud noise occurs, glutathione levels drop because it is trying to counteract those toxic free radicals. After awhile, glutathione becomes depleted. NAC can be taken up by the body and used to re-synthesize more glutathione, which is then available to act as the natural antioxidant to reduce the stress and neutralize the toxins.
Several studies in both animals and humans have shown the protective effects of NAC against noise-induced hearing loss. One study on chinchillas demonstrated that administering NAC up to 48 hours after auditory trauma and continuing for up to 10 days afterward, was effective in treating acute acoustic trauma. (2)
A study on 363 human volunteers given oral doses of NAC before noise exposure compared them with a control group that was given placebo. The study showed the protective effects of NAC were prominent for noise-induced hearing loss. (3)
A Taiwanese study of male workers in noisy environments provided doses of NAC in the amount of 1200 mg/day. The study found NAC may prevent noise-induced hearing loss among occupationally noise-exposed men. (4)
NAC has been shown to protect against mild traumatic brain injury. This is the most common battlefield injury in Southwest Asia and is commonly referred to as concussion. Eighty one combat individuals were assigned to receive either N-acetyl cysteine or a placebo for 7 days after injury. Outcome measures were the evaluation of dizziness, hearing loss, headache, memory loss, sleep disturbances and neurocognitive dysfunction. Analysis revealed that subjects receiving NAC within 24 hours of blast had an 86% chance of complete symptom resolution with no side effects versus 42% for those seen in the same time frame who received placebo. (5)
There are over 200 ototoxic medications, both prescription and over-the-counter, that can damage hearing and cause tinnitus. The mechanism of action seems to be similar to that of noise trauma; the drugs potentiate glutamate receptors in the cochlea that promote degradation of hair cells and neurons. This in turn leads to a cascade of free radicals, which further destroys the hair cells and neurons.
Once again, NAC is found to be very helpful in reducing the incidence of increased hearing loss and tinnitus if used prior to or very shortly after exposure. In one study, dialysis patients were treated with the aminoglycoside antibiotic, gentamicin. Gentamicin is associated with several side effects including permanent ototoxicity.
Forty patients were enrolled into control (placebo) and active (NAC) groups with an average therapy duration of 15 days. They were then monitored for hearing loss and tinnitus. At both 1 and 6 weeks after completion of the antibiotic therapy, there were significantly more patients exhibiting ototoxicity in the control group compared with the group receiving NAC. Additionally, significantly more patients in the control group had bilateral ototoxicity. (6)
Another study conducted on patients who were treated with aminoglycoside antibiotics and vancomycin, a known ototoxic medication, showed patients taking NAC had better hearing function test results 4 weeks after the treatment compared with those in the control group. (7)
Finally, a study was conducted concerning the medication cisplatin. This is a platinum based chemotherapy drug, which is extremely ototoxic. In this case, twenty cisplatin treated patients were subjected, under local anesthesia, to transtympanic infusions of NAC. This means NAC was injected through the eardrum into the middle ear. Each patient had one ear treated and the other was used as a control. Results were in treated ears there was no significant change in auditory thresholds at 8000 Hz. At the same frequency, the changes in auditory thresholds were significantly larger for the control ears. (8)
The benefits listed above are wonderful for those of us with tinnitus who want to ensure that it will not worsen. I have been exposed on a number of occasions to sudden loud sounds and a few times to dangerous ototoxic medications. Thanks to the great effects of NAC, and also Arches Tinnitus Formula, which I use continuously, I have not had any significant worsening of my tinnitus.
There is very little information on dosages in the previous studies. I will address that in the next section.
Good Health and NAC
The following is largely gleaned from an article on N-acetyl cysteine from the pages of the Life Extension Foundation magazine in May, 2010. The article uses extensive documentation to cite the clinical studies that support their findings. Rather than cite all of these, I will provide the link to the article itself, in References below, so interested persons can read the entire article. (9)
There are many other benefits to taking NAC besides noise exposure and ototoxic medications. One feature of this supplement has saved thousands of lives in recent years.
Acetaminophen is the active ingredient in Tylenol and many other over-the-counter pain medications. Unfortunately, Tylenol and the like are toxic to the liver. Acetaminophen toxicity is the number one cause of acute liver failure in the United States. Too much acetaminophen overwhelms the body’s glutathione reserves, which creates widespread and irreversible liver damage. The FDA has approved the use of NAC for treatment of acetaminophen toxicity. NAC is nearly 100% effective in protecting the liver when it is given within 8 hours of acute acetaminophen ingestion.
NAC is a potent agent that counteracts the effects of influenza. Even the H5N1 virus, commonly known as the bird flu, is subject to its protection. All forms of influenza produce a massive release of inflammatory products referred to as cytokines. These molecules make disease worse by producing fever, inflammation and tissue destruction. If left unchecked, they can lead to shock and death.
In early 2010 it was discovered that NAC offers dual protection against both common influenza and bird flu. It inhibits virus replications and moderates pro-inflammatory cytokine molecules, holding out the promise of protection in the event of a global flu pandemic.
In a large study of older adults who took 600 mg NAC twice daily for 6 months, only 25% of those experienced flu-like symptoms as compared with 79% in the placebo group. Even in those who did experience the flu, there was a significant reduction in illness and length of time confined to bed among the NAC participants.
NAC has been used for over 30 years in conventional medicine as an inhaler to reduce the viscosity of mucus, which helps it to clear faster from the body.
Chronic Obstructive Pulmonary Disease (COPD) includes chronic bronchitis and emphysema. This is a rapidly growing problem in the world population. COPD is the result of years of oxidative damage to delicate lung tissue accompanied by chronic inflammation. Over time, damaged airways may become infected with dangerous bacteria leading to still more inflammation.
Due to its ability to reduce free radicals and stop inflammation, NAC is fast becoming a main treatment protocol for COPD. A pilot study of adults with chronic bronchitis and positive bacterial culture demonstrated that 600 mg of NAC twice daily led to a near doubling of the rate of bacterial eradication compared to standard therapy. It also reduced the number and duration of acute episodes.
Emphysema can be the unfortunate end point of advanced COPD when lung tissue breaks down and loses the ability to exchange oxygen and carbon dioxide. Animal studies have shown NAC effectively reduces COPD lung damage and emphysema.
There are several other studies on NAC and COPD that further show the efficacy of this remarkable compound.
Oxidative stress and inflammation are closely linked to insulin resistance and rising blood glucose levels. Human studies on NAC to improve insulin sensitivity have recently appeared. Women with polycystic ovary syndrome (PCOS) typically have profound insulin resistance. A study showed 1800 mg of NAC daily helped improve insulin resistance among this group of women.
NAC has multiple anti-cancer activities acting at multiple targets to provide layers of cancer protection against a large variety of cancer types. NAC induces programmed cell death (apoptosis) in multiple types of human cancer cells and also stops DNA synthesis, preventing cancer cells from replicating.
A study conducted on otherwise healthy cigarette smokers found 600 mg NAC twice daily showed a significant reduction in early markers of cancer developing in lung fluid. Another study showed a 40% reduction in colorectal polyps by people taking 600 mg per day., thereby reducing chances of colorectal cancer.
Again, numerous other studies show the ability of NAC to prevent cancer. I urge interested readers to read the entire article from the Life Extension Foundation.
Normal doses of NAC are in the 600 to 1,800 mg per day range. Studies have shown doses up to 2,000 mg per day are safe and effective. I take 1,000 mg NAC twice daily and have done so for many years. I believe everyone should use NAC for its ability to promote health and prevent disease. Those of us with tinnitus have another reason to use it for protecting our hearing from further deterioration.
1 – http://audiologyonline.com/interviews/interview-with-richard-kopke-m-1447.
2 – Choi CH, Chen K, Du X, Floyd RA, Kopke RD. Effects of delayed and extended antioxidant treatment on acute acoustic trauma. Free Radic. Res. 2011 Oct;45(10):1162-72.
3 - Ge Z, Ma S, Jia X, Song L. Study of protective effects on noise-induced hearing loss using N-acetyl cysteine. Lin Chung Er Bi Yan Hou Tou Jing Wai Ke Za Zhi. 2011 Nov;25(22):1040-1.
4 – Lin CY, Wu JL, et. al. N-acetyl cysteine against noise-induced temporary threshold shift in male workers. Hear Res. 2010 Oct 1;269(1-2):42-7.
5 – Hoffer ME, Balaban C, Slade MD, Tsao JW, Hoffer B. Amelioration of acute sequelae of blast induced mild traumatic brain injury by N-acetyl cysteine: a double-blind, placebo controlled study. PLoS One. 2013;8(1):e54163.
6 – Feldman L, Efrati S, Eviatar E, et. al. Gentamicyin-induced ototoxicity in hemodialysis patients is ameliorated by N-acetyl cysteine. Kidney Int. 2007 Aug;72(3):359-63.
7 – Tokgoz B, Ucar C, et. al. Protective effect of N-acetyl cysteine from drug-induced ototoxicity in uraemic patients with CAPD peritonitis. Nephrol. Dial. Transplant. 2011 Dec;26(12):4073-8.
8 – Riga MG, Chelis L, Kakolyris S, et. al. Transtympanic injections of N-acetyl cysteine for the prevention of cisplatin-induced ototoxicity: a feasible method with primising efficacy. Am. J. Clin. Oncol. 2013 Feb;36(1):1-6.
9 – http://www.lef.org/magazine/mag2010/may2010_N-Acetyl-Cysteine_01.htm