Targeted Nutritional Therapies
Antioxidants are compounds that have the ability to neutralize damaging reactive oxygen species (ROS). Since ROS are involved in the development and progression of tinnitus and hearing loss, antioxidants represent a promising therapeutic strategy (Sergi 2004; Savastano 2007; Joachims 2003).
N-acetyl cysteine (NAC) is a naturally occurring antioxidant that has been used for years to treat acetaminophen overdose and break up mucus; it also increases the production of glutathione, one of the most prevalent antioxidants in the body (Kopke 2007). NAC has been studied as a potential therapeutic agent to protect hair cells from damage due to excessive noise as well. A 2011 study on military recruits found that NAC was able to protect the cochlea from damage due to noise from firing a gun in an enclosed space (Lindblad 2011). Animal studies have also found that NAC has a protective effect against continuous loud noises (Lorito 2006; Bielefeld 2007) as well as impulse noise (Kopke 2005). Another animal study showed that NAC may reduce noise-induced hearing loss even when administered after exposure to dangerous levels of noise (Coleman 2007). NAC has generated interest in the field of hearing loss because it is safe for human consumption and has already been approved for some uses in humans (e.g., treatment of acetaminophen toxicity) (Kopke 2007).
Mitochondria are the energy powerplants of the cell. They are also the site of ROS production, especially when the cell is under stress. In cochlear hair cells, mutations in mitochondrial DNA and declining function of the mitochondria have been found to cause age-induced hearing loss (Yamasoba 2007). As a result, compounds that help maintain mitochondrial health, such as acetyl-L-carnitine, may help protect cells from damage. Animal studies have found that acetyl-L-carnitine is able to protect the cochlea from both continuous and impulse noise damage as well as prevent loss of hair cells (Kopke 2002; Kopke 2005). Acetyl-L-carnitine was also found to reduce mutations in mitochondrial DNA, suggesting that it could prevent not only noise-induced hearing loss, but also age-related hearing loss (Seidman 2000). Much like NAC, acetyl-L-carnitine appears to be effective even when administered after exposure to loud noise(s) (Coleman 2007; Du 2012). In one animal study, acetyl-L-carnitine was shown to protect against ototoxicity induced by the chemotherapeutic drug cisplatin (Gunes 2011).
Lipoic acid has been found to reduce age-related hearing loss (Seidman 2000). Preliminary animal studies have also found that lipoic acid can help protect against noise-induced hearing loss and preserve inner-ear mitochondrial function (Diao 2003; Peng 2010). This may be partly due to the effect it has on glutathione (i.e., a naturally occurring antioxidant in the body). Studies have found increasing glutathione levels help protect the cochlea from damage due to loud noises (Le Prell 2007). In one laboratory study, lipoic acid was shown to increase glutathione levels in nerve cells, protecting them from damage (Jia 2008). Lipoic acid may also be able to counteract the action of toxins (e.g., carbon monoxide) that aggravate the effects of noise and make normally safe levels of volume harmful to the ear (Pouyatos 2008). In a clinical trial among 46 elderly subjects with hearing loss, 8 weeks of treatment with lipoic acid (60 mg/day) combined with two other free radical scavengers (vitamin C [600 mg/day] and rebamipide [300 mg/day]) significantly improved hearing at all frequencies tested (Takumida 2009).
Dietary supplementation with vitamins that have antioxidant capabilities can help protect the hair cells of the cochlea. One animal study showed that a 35-day pretreatment regimen of vitamin C may be able to protect against noise-induced hearing loss (McFadden 2005). Similarly, supplementing animals with certain forms of vitamins A and E have shown significant protective effects (Hou 2003; Ahn 2005). The length of time vitamins need to be taken prior to noise exposure may vary depending on the vitamin. For example, vitamin E appears to be effective with three days of pretreatment, vitamin A may only require two days to be effective, and Vitamin C may require a longer pretreatment period. In addition, taking vitamins in combination may be more effective than any one of them alone (Le Prell 2007). For example, a combination of B-vitamins, vitamins C & E, and L-carnitine protected rodents from cisplatin ototoxicity (Tokgoz 2012).
Folate and Vitamin B12
Folate and vitamin B12 are important for the functioning of many cells in the body, including nerve cells. They also help reduce levels of homocysteine, a potentially toxic compound found in the body. Elevated homocysteine levels are linked to an increased risk of hearing problems (Gok 2004; Gopinath 2010). Vitamin B12 injections (1 mg for 7 days followed by 5 mg on day 8) protected against noise-induced hearing loss in healthy volunteers aged 20 to 30 years (Quaranta 2004). Researchers have found that patients with low levels of folate in their blood are more likely to develop hearing loss (Gok 2004; Lasisi 2010; Gopinath 2010), and that low vitamin B12 levels are associated with hearing loss (Gok 2004) and tinnitus (Shemesh 1993).
Because loud noise impairs blood flow to the cochlea, researchers have also examined compounds that could help improve circulation to the hair cells and prevent their death. Magnesium is known to help expand blood vessels and improve circulation; it also helps control the release of glutamate, one of the major contributors to noise-induced hearing loss (Le Prell 2011). Animal studies have found that magnesium deficiency increases the risk of noise-induced hearing loss (Sendowski 2006b; Scheibe 2002). A combination of magnesium and other antioxidants may synergistically prevent hearing loss, potentially because magnesium’s ability to increase blood flow also helps transport the protective antioxidants (Le Prell 2011). Other animal studies have determined that magnesium can protect against impulse noise damage (Sendowski 2006a; Haupt 2003). Magnesium’s benefits have been demonstrated in human trials as well; magnesium supplementation (122 mg daily for ten days) reduced noise-induced hearing loss in men aged 16-37 years (Attias 2004). Studies have also found that both intravenous magnesium and oral magnesium supplementation may be beneficial for other types of hearing loss, such as sudden sensorineural hearing loss (Gordin 2002; Coates 2010).
Melatonin, a hormone critical for healthy sleep (Wurtman 2012), has powerful antioxidant properties. Animal studies have found that it is effective at preventing hearing damage after exposure to loud noises (Karlidag 2002; Bas 2009). It is also effective at treating other types of hearing loss caused by ROS, such as due to the chemotherapy drug cisplatin (Lopez-Gonzalez 2000). Researchers have discussed the potential for melatonin to act as a protectant against age-related hearing loss (Martinez 2009). For example, it was noted in a study that low plasma levels of melatonin were associated with significant high-frequency hearing loss among elderly subjects (Lasisi 2011).
Additionally, melatonin has been tested as a treatment for tinnitus, both in combination with the medication sulpiride (an atypical antipsychotic) and on its own. On its own, melatonin provides relief from tinnitus, especially in people with significant sleep problems (Rosenberg 1998; Megwalu 2006; Reiter 2011).When combined with sulpiride, melatonin reduces the perception of tinnitus by diminishing the activity of dopamine, a chemical in the brain. In one study, sulpiride alone relieved tinnitus in 56% of subjects while melatonin alone reduced tinnitus in 40%. However, when used together, 81% of subjects reported relief from their tinnitus symptoms (Lopez-Gonzalez 2007).
Ginkgo biloba, a commonly used herbal supplement, has attracted interest as a means of protecting against hearing loss as well as a treatment for tinnitus. Early animal studies found that when a standardized preparation of Ginkgo biloba extract was given as a supplement to animals, it reduced behavioral manifestations of tinnitus (Jastreboff 1997). This extract, at a dose of 160 mg daily over a 12 week period, was also effective at reducing symptoms in humans (Morgenstern 2002). However, other studies have found negligible or no effect (Hilton 2010; Canis 2011); therefore, more research is needed in this area. Ginkgo biloba may also be effective at preventing hearing loss that causes tinnitus; an animal study found that a Gingko biloba extract was able to reduce drug-induced oxidative damage to hair cells in the cochlea (Yang 2011).
Coenzyme Q10(CoQ10) supports mitochondrial function and has significant antioxidant properties (Quinzii 2010). Animal studies have found that supplementation with CoQ10 reduced noise-induced hearing loss and the death of hair cells (Hirose 2008; Fetoni 2009, 2012). Human studies have also yielded promising results, as 160-600 mg of CoQ10 daily was found to reduce hearing loss in people with sudden sensorineural hearing loss and presbycusis (Ahn 2010; Salami 2010; Guastini 2011). Also, a small preliminary trial found that CoQ10 supplementation alleviated tinnitus in those whose CoQ10 blood levels were initially low (Khan 2007). Another small trial found CoQ10 may slow progression of hearing loss associated with a mitochondrial genetic mutation (Angeli 2005).
Zinc, a mineral involved in many physiological processes (including nervous system function), has antioxidant and anti-inflammatory properties (Frederickson 2000; Prasad 2008). Evidence suggests that inadequate zinc intake may be associated with impaired hearing (Kang 2012). Researchers have found that zinc supplementation may be helpful in treating some forms of hearing loss (Yang 2010). In addition, low levels of zinc correlate with perceived loudness of tinnitus in afflicted individuals (Arda 2003).
Omega-3 fatty acids
Long-chain omega-3 (n-3) polyunsaturated fatty acids, long recognized as important for health, may also affect hearing loss; a preliminary study found that participants with the highest blood levels of these beneficial fats suffered the least amount of hearing loss over time (Dullemeijer 2010). In another study, greater fish or fish oil consumption was associated with less hearing loss among nearly 3,000 subjects over 50 years of age. The authors remarked that “dietary intervention with n-3 PUFAs could prevent or delay the development of age-related hearing loss” (Gopinath 2010).
Taurine plays a vital role in hearing. In fact, studies have found that in some cases, taurine can reverse the biochemical processes behind hearing loss (Liu 2006; Liu 2008a). Other studies have demonstrated that taurine can almost completely eliminate the ringing in the ears associated with tinnitus (Brozoski 2010).
Much of the damage to hearing occurs not in the mechanical parts of the ear, but rather in the nerve cells that convert sound waves into the electrical energy that is perceived in our brains. Like other nerve cells, these so-called “hair cells” depend on the flow of calcium ions into and out of the cell. Taurine helps restore and control normal calcium ion flow in auditory cells (Liu 2006; Liu 2008b).
Taurine improves the hearing ability in animals exposed to drugs like the antibiotic gentamicin, which is notoriously toxic to hearing (Liu 2008a). And in a boon for the 17% of us troubled by chronic tinnitus (ringing in the ears), taurine may be helpful in quieting the noise (Galazyuk 2012). Animal studies using human equivalent doses of 700 mg to 3.2 grams per day of taurine over the course of several weeks demonstrate near-complete resolution of tinnitus with taurine supplementation (the animals had been trained in tasks that are sensitive to distraction by tinnitus) (Brozoski 2010). And a human pilot study has shown encouraging results, with 12% of people responding to taurine supplementation (Davies 1988).