About 15% of adults in the United States are affected by a certain degree of hearing loss. Up to two thirds of adults over 65 and 80% of over 85 have a reduced hearing. In the American population, hearing loss is conducted hypertension, smoking, diabetes and greater risk of hospitalization. Because hearing loss can have a significant impact on a person, and because the causes are not fully understood, the search for new risk factors is ongoing. For example, sudden sensorineural deafness (SNHL) has recently been considered associated with martial anemia or iron deficiency (AMA). Worldwide, the AMA affects at least 1.5 billion people, of which about 8 million in the United States alone. A team of experts led by Dr. Kathleen Schieffer of the Pennsylvania State College of Medicine decided to investigate the relationship between AMA and hearing loss in more detail. AMA is a condition in which there is talk of a lack of iron. Because red blood cells carry oxygen around the body, anemia reduces the amount of oxygen available to the tissues. Because anemia is easy enough to treat, any link between the two conditions could be important.
The research team produced data from the electronic medical records of the Penn State Milton S. Hershey Medical Center in Hershey, Pennsylvania. In total, data from 305,339 adults aged 21 to 90 years were examined, with 43% of the male cohort and a mean age of 50 years. Observing the levels of ferritin and hemoglobin, the presence of AMA was retrospectively diagnosed. The team also collected information regarding the patient’s hearing. Public opinion – a cause of problems with the inner ear bones, or SNHL – damage to the cochlea or nerve pathways that passed from the inner ear to the brain, deafness and unspecified hearing loss. Once the data were analyzed, the team found a relationship: SNHL and combined hearing loss (SNHL and conductive hearing loss in the same individual) were both negative associated with AMA. The authors conclude: “There is an association between adults and hearing loss, because anemia could be linked to hearing loss is not yet fully understood, but there are some mechanisms hypothesized. of blood to the inner ear through the labyrinthine artery is very sensitive to ischemic injury, which could certainly play a role.
The cochlea is highly susceptible to ischemic damage because only the labyrinthine artery supplies blood to this area. It has been shown that IDA is a potential risk factor for ischemic stroke due to lower levels of hemoglobin leading to reduced oxygen carrying capacity. Individuals with vascular disease have been shown to have a higher risk of developing sudden SNHL. Another potential vascular mechanism linking IDA and hearing loss is the increased risk of patients with IDA for reactive thrombocytosis. Iron is a regulator of thrombopoiesis and previous associations between blood loss and thrombocytosis have been established. This hypothesis is further confirmed by a clinical case that showed that acute SNHL in a patient with marked thrombocytosis was reversed after plasmapheresis. Furthermore, individuals with vascular disease are known to be more susceptible to sudden SNHL. Therefore, blood supply is clearly an important factor in hearing loss. Another potential mechanism involves myelin, which is important for the efficient conduction of signals along nerve fibers. The reduction of iron in the body interferes with the saturase and desaturase enzymes of fatty acids, both important for the production of cellular energy and, consequently, of myelin. If the lining of the myelin of the auditory nerve is damaged, the hearing could be reduced.
The next step for researchers will be to understand whether food or direct iron supplementation could positively influence hearing loss. If it can improve damaged hearing or reduce hearing loss, it could be an economical way to minimize this highly prevalent and disabling medical condition.
- edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
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