Up to two thirds of adults over 65, and 80 percent of those over 85, have reduced hearing.
Because hearing loss can have a significant impact on an individual's well-being, and because the causes are not fully understood, research into novel risk factors is ongoing.
For instance, sudden sensorineural hearing loss (SNHL), during which an individual's hearing is reduced severely over a 72-hour period, was recently shown to be associated with iron deficiency anemia (IDA).
Researchers led by Kathleen M. Schieffer, from the Pennsylvania State University College of Medicine, set out to investigate IDA's relationship with hearing loss in more detail.
Iron deficiency anemia and hearing loss
IDA is a common condition that is caused by a lack of iron in the body, leading to a reduced number of red blood cells. Because red blood cells ferry oxygen around the body, IDA reduces the amount of oxygen available to tissues.
Worldwide, IDA affects hundreds of millions of people, including an estimated 5 million people in the U.S.
Because hearing loss impacts approximately 15 percent of U.S. individuals, and because IDA is generally easy to treat, any ties between the two conditions could be important.
The research team used data from deidentified electronic medical records from the Penn State Milton S. Hershey Medical Center in Hershey, PA. In total, data from 305,339 adults aged 21-90 was investigated, with 43 percent of the cohort being male, and with an average age of 50. By observing ferritin and hemoglobin levels, IDA was diagnosed retrospectively.
The team also gathered information regarding the patient's hearing. They looked separately at conductive hearing loss - due to problems with the bones of the inner ear, or SNHL - damage to the cochlea or nerve pathways passing from the inner ear to the brain, deafness, and unspecified hearing loss.
Once the data had been analyzed, the team found a relationship: SNHL and combined hearing loss (SNHL and conductive hearing loss in the same individual) were both significantly associated with IDA.
The authors conclude:
"An association exists between IDA in adults and hearing loss. The next steps are to better understand this correlation and whether promptly diagnosing and treating IDA may positively affect the overall health status of adults with hearing loss."
How does anemia influence hearing?
Why IDA might be linked to hearing loss is not yet fully understood, but there are a few potential pathways. For instance, blood supply to the inner ear via the labyrinthine artery is highly sensitive to ischemic damage (damage caused by reduced blood flow), which could certainly play a role.
Additionally, individuals with vascular disease are known to be more susceptible to sudden SNHL. Blood supply is, therefore, clearly an important factor in hearing loss.
Another potential mechanism involves myelin, a waxy substance that coats nerves and which is important for the efficient conduction of signals along nerve fibers. Reduced iron in the body causes the breakdown of lipid saturase and desaturase, both of which are important in energy production and, consequently, the production of myelin. If the myelin coating the auditory nerve is damaged, hearing could be reduced.
The next step for researchers will be to understand whether iron supplementation might positively affect hearing loss. If it can improve damaged hearing or reduce hearing loss, it could be a cost-effective way to minimize a highly prevalent and disruptive medical condition.
Association of iron deficiency anemia with hearing loss in US adults, Kathleen M. Schieffer et al., JAMA Otolaryngology - Head & Neck Surgery, doi: 10.1001/jamaoto.2016.3631, published online 29 December 2016.
JAMA news release, accessed 4 January 2017 via EurekAlert.
Iron deficiency anemia: A common and curable disease, Jeffery L. Miller, Cold Spring Harbor Perspectives in Medicine, doi: 10.1101/cshperspect.a011866, published online July 2013.
National Institute on Deafness and Other Communication Disorders, Quick statistics about hearing, accessed 4 January 2017.
Sudden sensorineural hearing loss associated with iron-deficiency anemia: a population-based study, SD Chung et al., JAMA Otolaryngology - Head & Neck Surgery, doi: 10.1001/jamaoto.2014.75, published online May 2014, abstract.