However, emerging evidence now indicates that the problem may have more to do with lifestyle than simply growing old. Studies show that a number of environmental factors, including noise pollution, diet, chemical exposures and even prescription drugs, can contribute to hearing loss. Crucially, the evidence suggests that hearing loss may well be a preventable condition.
Repeated exposure to loud noise is one of the most common causes of hearing loss. When noise is too loud-in general, this means above 85 decibels (dB), the level of noise made by heavy city traffic-prolonged exposure can destroy the sensitive hair cells in the inner ear. These hair cells move as sound waves travel through the ear structures, and the movement is converted to nerve impulses that are interpreted by the brain as sound.
A single loud noise, such as a gunshot blast, can permanently harm these inner-ear structures-although years of exposure to less intense sounds, such as loud music, can also cause irreversible damage (Pediatrics, 2001; 108: 40-3). As well as impaired hearing, such exposure to loud noise can lead to tinnitus (persistent ringing in the ear), hyperacusis (extreme oversensitivity to sound) and other hearing disorders (Int J Audiol, 2003; 42: 279-88).
Traditionally, noise-induced hearing loss (NIHL) has been considered a disease of adults who worked in noisy occupations or used firearms. How-ever, there's growing concern that children and young adults are now developing the condition as a result
of overexposure to amplified music, especially through the use of personal music devices such as MP3 players.
As a recent article in the British Medical Journal pointed out, "The devices increasingly use earphones that insert into the ear canal which produce higher sound levels in the ear than 'over-the-ear earphones' used at the same volume. These sound levels can exceed 120 decibels, similar in intensity to a jet engine" (BMJ, 2010; 340: c1261). Indeed, several small, controlled studies have found that personal music players are associated with poorer hearing function in adolescents and young adults (Noise Health, 2009; 11: 132-40; J Otolaryngol Head Neck Surg, 2008; 37: 718-24).
Although more research is needed to clarify the role of personal music players in hearing loss, in the meantime, the advice is simple: turn down the volume and take regular breaks from using them. As a rule of thumb, if the music is uncomfortable for you to listen to, or if you can't hear any external sounds when you've got your headphones on, then the volume is too loud.
In addition, it should be borne in mind that the higher the volume of the sound, the shorter the time you should be listening to it. University of Colorado researchers have placed a safe listening limit of 4.6 hours per day on an iPod played at 70-per-cent
of its volume if you're using stock iPod earphones. However, this duration falls precipitously to just five minutes if the volume is cranked up to maximum (www.colorado.edu/news/releases/2006/346. html).
Other ways to reduce the chances of developing NIHL include:
wearing hearing protectors, such as earplugs or earmuffs, when you know you're going to be around dangerously loud noise. Lawn-mowers, power tools, rock concerts and motorcycles, for example, can all cause permanent damage to hearing if you don't wear ear protection;
turning the volume down on your stereo, television and car radio. Also, avoid buying noisy toys, appliances or tools when there are quieter alternatives, and don't use several noisy machines at the same time. What's more, don't try to drown out unwanted noise with other sounds: for example, don't turn up the volume on your car radio or headset to drown out traffic noise, or turn up the tele-vision volume while vacuuming;
using sound-absorbing materials to reduce noise at home and at work. Rubber mats can be placed under noisy kitchen appliances, computer printers and typewriters to cut down on noise. Curtains and carpeting also help to reduce indoor noise, and double-glazed windows can reduce the amount of outside noise that can penetrate into the home or workplace;
having your hearing checked regularly, especially if you are frequently exposed to loud noise at either work or play.
Besides noise, what we eat can also have an impact on our hearing. High fat and cholesterol consumption can lead to high blood-cholesterol levels and the production of free radicals. This, in turn, can lead to impaired hearing by reducing the flow of oxygen and nutrients to the inner ear. Indeed, a study conducted in Taiwan-the largest of its kind-found that those who had high levels of triglycerides (a form of fats made by the body) in their blood had a significantly greater risk of developing NIHL (Otolaryngol Head Neck Surg, 2007; 137: 603-6).
Similarly, researchers in Turkey reported that people with NIHL were highly likely to have hyperlipidaemia-an excess of cholesterol and fatty acids in the blood. The team also found that a low-cholesterol diet helped to improve hearing, and alleviated tinnitus in these patients (Int Tinnitus J, 2007; 13: 143-9).
On the other hand, certain fats may have an important role to play in protecting our hearing. A study recently published in the American Journal of Clinical Nutrition found that consumption of omega-3 fatty acids-in particular, the long-chain variety found in fish oil-reduced the risk of age-related hearing loss. Participants who consumed two or more servings of fish per week had a 42-per-cent lower risk of developing presbycusis compared with those who ate less than one serving a week. In addition, in those who already have hearing loss, fish consumption appears to prevent it from getting worse (Am J Clin Nutr, 2010; 92: 416-21).
However, much of the research on nutrition and hearing loss has focused on antioxidants. Emerging evidence shows that free-radical formation in the inner ear plays a key role in the development of NIHL. Antioxidants, which mop up free radicals, may therefore be an effective intervention.
Animal studies (so the results may not necessarily apply to humans) have demonstrated that a variety of dietary antioxidants, including vitamins A, C and E, can reduce NIHL when given prior to noise exposure. A combination of high-dose vitamin A (2.1 mg/kg), vitamin C (71.4 mg/kg) and vitamin E (26 mg/kg) plus magnesium (343 mg/kg) can prevent NIHL when taken one hour prior to noise exposure and continued once a day for five days subsequently (Free Radic Biol Med, 2007; 42: 1454-63). It appears that the vitamins work in synergy to reduce both free-radical formation and inner-ear hair-cell damage, while the magnesium preserves blood flow to the inner ear, as this is also affected by loud noise.
Remarkably, antioxidants delivered as late as three days after noise exposure were still found to be beneficial (Neuroscience, 2005; 134: 633-42)-although, again, these animal test results may not necessarily apply to humans.
Nevertheless, there is evidence to support the use of magnesium for human hearing. In a two-month, double-blind, placebo-controlled study of 300 Israeli military recruits, daily supplementation with 167 mg of magnesium significantly helped to protect their hearing against noise-induced damage (Am J Otolaryngol, 1994; 15: 26-32). Another Israeli study of 20 young men found similar results (Clin Otolaryngol Allied Sci, 2004; 29: 635-41).
Other nutrients that may be involved in ear health are folate and vitamin B12. A recent study found that, among men aged 60 years or over, those with the highest folate intakes had the lowest risk of hearing loss (Otolaryngol Head Neck Surg, 2010; 142: 231-6).
In an earlier study, which looked at a group of army personnel exposed to military noise, vitamin B12 deficiency was commonly found among those with NIHL and/or chronic tinnitus. Interestingly, 12 patients who had vitamin B12 replacement therapy saw their symptoms improve (Am J Otolaryngol, 1993; 14: 94-9).
Drugs and other toxins
A staggering range of drugs are associated with hearing loss-from painkillers to oral contraceptives. A recent study has revealed that the regular use of aspirin, acetaminophen (paracetamol) and non-steroidal anti-inflammatory drugs (NSAIDs) can significantly increase the risk of hearing loss in men (Am J Med, 2010;
Antibiotics, especially aminoglycosides such as amikacin, gentamicin and tobramycin, chemotherapy drugs, hormone replacement therapy (HRT), antimalarials and loop diuretics have also all been shown to have ototoxic (ear-damaging) effects (Braz J Otorhino-laryngol, 2006; 72: 836-44; Hear Res, 2009; 252: 29-36).
Apart from medication, a number of other agents have also been linked to hearing loss, including pesticides, toluene, styrene, ethylbenzene, carbon disulphide, lead and mercury (Braz J Otorhinolaryngol, 2006; 72: 836-44).
Smoking also appears to damage hearing-possibly by affecting the antioxidative mechanisms of the body or reducing the blood circulation to the hearing system. Indeed, a study of people working in noisy environments found that long-term smokers were more likely to develop permanent hearing loss than non-smokers (Clin Otolarygol, 2005; 30: 517-20).
Another found that smokers had a 69-per-cent increased risk of hearing loss compared with non-smokers, and even non-smokers living with smokers were more likely to suffer hearing loss, too (JAMA, 1998; 279: 1715-9). Indeed, infants exposed to cigarette smoke had a fivefold greater incidence of hearing loss than unexposed infants
(Ir Med J, 1992; 85: 111-2).
A sound solution
So far, the evidence suggests that hearing loss is not something that should simply be accepted as an inevitable part of ageing. It is a condition that can be prevented by paying attention to what we eat, to our noise exposure and to the toxins that surround us on a regular basis.
Ultimately, if you follow a healthy, balanced diet that includes plenty of antioxidants and good fats, and focus on turning the volume down in your life, you should be well on the way to ensuring the sweet sounds of good hearing for years to come.
Can hearing loss be treated?
Usually, a hearing aid is the only 'treatment' for age-related hearing loss, but there's now evidence to suggest that certain herbs and supplements may be able to restore hearing loss.
Antioxidants are among the most promising therapies for hearing loss. In one study, alpha-lipoic acid (60 mg/ day), vitamin C (600 mg/day) and the drug rebamipide (300 mg/day), an amino-acid derivative that scavenges damaging free radicals, were given orally for at least 8 weeks to 46 elderly patients with hearing loss. At the end of the treatment, hearing levels were significantly improved at all frequencies tested (Acta Otolaryngol, 2009; 129: 36-44).
Another study-a placebo-controlled trial this time-demonstrated that supplementing with both vitamins E (600 mg/day) and C (1200 mg/day) can be beneficial
for sudden-onset sensorineural hearing loss (nerve deafness) (Acta Otolaryngol, 2008; 128: 116-21).
Ginkgo biloba may be useful for hearing loss, accord-ing to several studies. In one, the herb was better than the conventional combined drug treatment when tested in 52 patients with acquired sensorineural hearing loss (Indian J Otolaryngol Head Neck Surg, 2000; 52: 212-9).
Although an optimal dose has yet to be established, in general, studies have used 30-200 mg daily, with the higher doses tending to provide better results.
Correcting nutritional deficiencies may help to restore hearing in some cases. Indeed, one study reported that zinc supplementation in patients who were marginally zinc-deficient improved tinnitus and sensorineural hearing loss in about one-third of elderly adults (Am J Otol, 1989; 10: 156-60).
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