Causes of and Risk Factors for Hearing Loss
A number of risk factors can predispose a person to hearing loss. Although advancing age is the most important risk factor, people with heart disease, high blood pressure, diabetes and an extensive smoking history are more likely to develop hearing loss (Helzner 2005; Bielefeld 2010). Otosclerosis, a condition involving abnormal bone growth within the middle ear, is associated with both conductive and sensorineural hearing loss (Liktor 2012; Ealy 2011; Bloch 2012; Deggouj 2009). In addition, hearing loss is more common in men (Agrawal 2008).
Noise Exposure. Repeated exposure to loud noises from occupational sources, recreational activities, or firearms strongly correlates with an increased risk of unilateral (hearing loss in one ear), bilateral (hearing loss in both ears), and high-frequency hearing loss (Agrawal 2008). According to a 2007 report, approximately 30 million Americans are exposed to dangerous levels of noise everyday, with 10 million adults and 5.2 million children affected by irreversible hearing loss due to excessive noise exposure (Seidman 2010). In addition, noise-induced hearing loss is the largest single category of compensated occupational disease in Europe (Mitchell 2009).
The National Institute of Occupational Safety and Health considers noise levels above 85 decibels to be harmful (Marsh 2011). Although sustained levels of loud noise are dangerous, impulse noise (i.e., large bursts of loud noise) can also damage hearing. In fact, research suggests that short exposure to very loud noise, such as that experienced by soldiers, can be more damaging to the auditory system than continuous noise (Clifford 2009).
Not only does excessive noise damage hearing, it may also increase blood pressure and heart rate, increase physiologic stress, and raise cortisol levels (Seidman 2010). Elevated cortisol levels are associated with an increased risk of osteoporosis, high cholesterol, hypertension, and insulin resistance (Tsigos 2002).
Ototoxic drugs. Some drugs have the potential to cause hearing loss or tinnitus because they are toxic to the ear or “ototoxic”. Examples of ototoxic drugs include high doses of aspirin, some antibiotics, some chemotherapy drugs, and some anti-inflammatory medications (Verdel 2008; Ligezinski 2002; Rybak 2007; Wecker 2004; Puel 2007). For example, high doses of aspirin in the range of 2,000 to 4,000 mg daily can cause tinnitus and hearing loss via peripheral effects on the cochlea and central effects on nerves involved in hearing. These effects usually subside within one to three days of discontinuing aspirin (Stolzberg 2012; McFadden 1984; Carlyon 1993; Day 1989). Risk of developing drug-induced hearing loss is greater in those with impaired kidney health or inner ear disorders (Ligezinski 2002).