Iron-Deficiency Anemia & Hearing Loss

Can Iron Deficiency Indicate Future Hearing Problems?

Researchers have recently discovered a possible link between iron-deficiency anemia and hearing loss—particularly those under the age of 45.
Conducted in Taiwan, the new research found that the rate of prior iron-deficiency anemia was 45% higher among those who experienced sudden sensorineural hearing loss than among controls (4.3% vs. 3.0%).  The correlation was more pronounced in those 44 years or younger. For those 60 years and older, there was no significant increase in the association between prior iron-deficiency anemia and sudden sensorineural hearing loss.
After analyzing the study’s data, Dr. Shih-Han Hung from Taipei Medical University Hospital said, “…I think having patients with hearing loss, whether sudden or not, checked for their iron status might be a reasonable recommendation.”
According to Dr. Hung, it is still unclear if complete correction of iron-deficiency anemia status would help directly avoid the development of hearing difficulties. However, early detection and management of both health issues will significantly benefit one’s quality of life.
Independent studies show that early acceptance of hearing difficulties and utilization of hearing devices can positively affect nearly every aspect of a person’s life as well as lessen their risk of developing other health concerns linked with untreated hearing loss, especially in children.

The association between iron deficiency anemia and hearing loss is explored in a recent study, published in JAMA Otolaryngology - Head & Neck Surgery. Could such a common blood condition impact our ability to hear?

Hearing loss and anemia appear to be linked, according to recent studies.

An estimated 15 percent of adults in the United States are affected by some degree of hearing loss.
Up to two thirds of adults over 65, and 80 percent of those over 85, have reduced hearing.
In the U.S. population, hearing loss is linked to poorer health, high blood pressure, smoking, diabetes, and hospitalization.
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.
Learn how anemia might raise the risk of death for stroke patients.

Written by Tim Newman

Iron deficiency anemia is a frequently occurring clinical disorder. Despite the suggested association with hearing loss in the literature, cochlear sequelae of iron deficiency have yielded conflicting results in experimental studies. Auditory function was tested in iron-deficient and normal male Wistar albino rats using distortion product otoacoustic emissions and auditory brainstem response audiometry for the clarification of the opposing results in the literature. Hemoglobin, hematocrit, serum iron and albumin levels were monitored to verify iron deficiency. Although dramatic differences in weight gain and blood test parameters were noted, no significant change in auditory function due to iron deficiency was detected.

IMPORTANCE Vascular events play a big part in the development of sudden sensorineural hearing loss (SSNHL), but only those associated with sickle-cell anemia have been previously associated with SSNHL. This study demonstrates an association between SSNHL and prior iron-deficiency anemia (IDA).OBJECTIVE To evaluate the association between IDA and SSNHL using a nationwide population-based database.DESIGN, SETTING, AND PARTICIPANTS In this case-control study in Taiwan, participants with SSNHL (n = 4004) were identified, and controls (n = 12 012) were randomly selected.MAIN OUTCOMES AND MEASURES Conditional logistic regression was used to calculate the ORs (95%CIs) for IDA in participants with SSNHL vs controls.RESULTS Of the 16 016 sampled participants, 533 (3.3%) had previously been diagnosed with IDA, including 172 (4.3%) participants with SSNHL and 361 (3.0%) controls. The χ2 test revealed a significant difference (P < .001) in the prevalence of prior IDA between participants with SSNHL and controls. By conditional logistic regression, we found that the OR for previous IDA among the participants with SSNHL was 1.34 (95%CI, 1.11-1.61) (P < .01)after adjusting for monthly income, geographic region, urbanization level, and comorbidities(ie, hypertension, diabetes, hyperlipidemia, renal disease, and coronary heart disease). The significant relationship between SSNHL and prior IDA was most pronounced among those 44 years or younger (adjusted OR, 1.91; 95%CI, 1.35-2.72) (P < .001) for the participants with SSNHL compared with controls, and the strength of this relationship decreased with age.CONCLUSIONS AND RELEVANCE There is an association between SSNHL and prior IDA.Patients with IDA, especially those younger than 60 years, should be more aggressively surveyed and managed to reduce hearing-related morbidities.

The Role of Red Blood Cells in Anemia

Red blood cells carry hemoglobin, an iron-rich protein that attaches to oxygen in the lungs and carries it to tissues throughout the body. Anemia occurs when you do not have enough red blood cells or when your red blood cells do not function properly. It is diagnosed when a blood test shows a hemoglobin value of less than 13.5 gm/dl in a man or less than 12.0 gm/dl in a woman. Normal values for children vary with age.
When you have anemia, your body lacks oxygen, so you may experience one or more of the following symptoms:

• Weakness
• Shortness of breath
• Dizziness
• Fast or irregular heartbeat
• Pounding or "whooshing" in your ears
• Headache
• Cold hands or feet
• Pale or yellow skin
• Chest pain

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Am I at Risk?

Many people are at risk for anemia because of poor diet, intestinal disorders, chronic diseases, infections, and other conditions. Women who are menstruating or pregnant and people with chronic medical conditions are most at risk for this disease. The risk of anemia increases as people grow older. People who engage in vigorous athletic activities, such as jogging or basketball, may develop anemia as a result of red blood cells breaking down in the bloodstream.
If you have any of the following chronic conditions, you might be at greater risk for developing anemia:

• Rheumatoid arthritis or other autoimmune disease
• Kidney disease
• Cancer
• Liver disease
• Thyroid disease
• Inflammatory bowel disease (Crohn disease or ulcerative colitis)

The signs and symptoms of anemia can easily be overlooked. In fact, many people do not even realize that they have anemia until it is identified in a blood test.
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Common Types of Anemia

Iron-deficiency anemia is the most common type of anemia. It happens when you do not have enough iron in your body. Iron deficiency is usually due to blood loss but may occasionally be due to poor absorption of iron. Pregnancy and childbirth consume a great deal of iron and thus can result in pregnancy-related anemia. People who have had gastric bypass surgery for weight loss or other reasons may also be iron deficient due to poor absorption.
Vitamin-deficiency anemia may result from low levels of vitamin B12 or folate (folic acid), usually due to poor dietary intake. Pernicious anemia is a condition in which vitamin B12 cannot be absorbed in the gastrointestinal tract.
Anemia and Pregnancy - Learn about the risk factors and symptoms of anemia during pregnancy.
Aplastic anemia   is a rare form of anemia that occurs when the body stops making enough red blood cells. Common causes include viral infections, exposure to toxic chemicals, drugs, and autoimmune diseases. Idiopathic aplastic anemia is the term used when the reason for low red blood cell production is not known.
Hemolytic anemia   occurs when red blood cells are broken up in the bloodstream or in the spleen. Hemolytic anemia may be due to mechanical causes (leaky heart valves or aneurysms), infections, autoimmune disorders, or congenital abnormalities in the red blood cell. Inherited abnormalities may affect the hemoglobin or the red blood cell structure or function. Examples of inherited hemolytic anemias include some types of thalassemia and low levels of enzymes such as glucose-6 phosphate dehydrogenase deficiency. The treatment will depend on the cause.
Sickle cell anemia is an inherited hemolytic anemia in which the hemoglobin protein is abnormal, causing the red blood cells to be rigid and clog the circulation because they are unable to flow through small blood vessels.
Anemia caused by other diseases   - Some diseases can affect the body's ability to make red blood cells. For example, some patients with kidney disease develop anemia because the kidneys are not making enough of the hormone erythropoietin to signal the bone marrow to make new or more red blood cells. Chemotherapy used to treat various cancers often impairs the body's ability to make new red blood cells, and anemia often results from this treatment.
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How is Anemia Treated?

The treatment for anemia depends on what causes it.
Iron-deficiency anemia is almost always due to blood loss. If you have iron-deficiency anemia, your doctor may order tests to determine if you are losing blood from your stomach or bowels. Other nutritional anemias, such as folate or B-12 deficiency, may result from poor diet or from an inability to absorb vitamins in the gastrointestinal tract. Treatment varies from changing your diet to taking dietary supplements.
If your anemia is due to a chronic disease, treatment of the underlying disease will often improve the anemia. Under some circumstances, such as chronic kidney disease, your doctor may prescribe medication such as erythropoietin injections to stimulate your bone marrow to produce more red blood cells.
Aplastic anemia occurs if your bone marrow stops producing red blood cells. Aplastic anemia may be due to primary bone marrow failure, myelodysplasia (a condition in which the bone marrow produces abnormal red blood cells that do not mature properly), or occasionally as a side effect of some medications. If you appear to have a form of aplastic anemia, your doctor may refer you to a hematologist for a bone marrow biopsy to determien the cause of the anemia. Meedications and blood transfusions may be used to treat aplastic anemia.
Hemolytic anemia occurs when red blood cells are destroyed in the blood stream. This may be due to mechanical factors (a leaky heart valve or aneurysm), infection, or an autoimmune disease. The cause can often be identified by special blood tests and by looking at the red blood cells under a microscope. The treatment will depend upon the cause and may include referral to a heart or vascular specialist, antibiotics, or drugs that suppress the immune system.
Talk with your doctor if you believe you may be at risk for anemia. Your doctor will determine your best course of treatment and, depending on your condition, may refer you to a hematologist, a doctor who specializes in blood disorders.
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Is Anemia Preventable?

While many types of anemia cannot be prevented, eating healthy foods can help you avoid both iron-and vitamin-deficiency anemia. Foods to include in your diet include those with high levels of iron (beef, dark green leafy vegetables, dried fruits, andnuts),vitamin B-12 (meat and dairy), and folic acid (citrus juices, dark green leafy vegetables, legumes, and fortified cereals). A daily multivitamin will also help prevent nutritional anemias; however, older adults should not take iron supplementsfor iron-deficiencyanemia unless instructed by their physicians.

 Iron deficiency anemia (IDA) is a blood condition in which the body fails to make enough healthy red blood cells. IDA is caused by a deficiency in iron, a mineral that acts as an important building block for red blood cell construction. It's the most common nutritional disorder in the world, affecting mostly women and children.
Who Is at Risk?
In the United States, 9 percent to 12 percent of non-Hispanic white women and close to 20 percent of black and Mexican-American women have iron deficiency anemia.
The two main causes of IDA are blood loss and low iron. Blood loss can occur from menstruation, recent major surgery or trauma or peptic ulcer disease, among other causes. Low iron may result from gastrointestinal diseases such as celiac sprue, Crohn's disease or ulcerative colitis; a diet low in iron; and history of a bariatric procedure like gastric bypass.
Pregnancy and breastfeeding increase iron requirements, so both are risk factors for IDA.
Children who drink more than 16 to 24 ounces of cow's milk a day are at an increased risk for IDA. Cow's milk can lead to blood loss by irritating the lining of the intestines and can interfere with iron absorption.
What Are the Symptoms?

Symptoms of Iron Deficiency Anemia
Fatigue	Shortness of breath
Weakness	Blue color to whites of the eyes
Irritability	Increased heart rate
Headache	Sore tongue
Pale skin	Pounding or "whooshing" sound in ears
Trouble concentrating	Lightheadedness upon standing
Brittle nails	Craving for ice or clay, called picophagia

How Is It Treated?
Treatment for IDA depends on its cause and severity and individual factors, including your age, health and medical history. Your health care professional may advise:

• taking supplemental iron, either in the form of pills or intravenous (IV) iron.
• eating more iron-rich foods, such as meats, poultry, seafood, dark leafy greens, egg yolks, legumes, oatmeal, peanut butter, raisins, prunes, apricots, soybeans, whole-wheat breads and iron-enriched bread, cereal, pasta and rice.
• in severe cases, your doctor may recommend getting a blood transfusion.

How Is It Prevented?
To prevent IDA, the best thing you can do is make sure you get sufficient iron in your diet. At times when your body requires extra iron, such as during pregnancy or breastfeeding, boost your iron intake even more with food and talk to your health care professional about iron supplements.

Anaemia and Tinnitus

Anaemia is a blood condition in which a person has a low level of haemoglobin in their blood or fewer red blood cells than normal. The most common type of anaemia is caused by iron deficiency, which results in fewer red blood cells. A low level of vitamin B12 can also cause Anaemia. Symptoms vary depending on the type of anemia you have and what causes it. The body uses iron to produce blood cells. These red blood cells store and carry oxygen around the body. If you have fewer red blood cells your body’s organs and tissues will receive less oxygen. One of the more common symptoms of anaemia is tinnitus and medical research shows a direct link between pulsatile tinnitus and iron deficient anaemia.
Diet can affect tinnitus in individuals in different ways. There is no definitive link to particular types of foods making tinnitus worse or better however there is a clear association between tinnitus and anaemia.

Pulsatile Tinnitus

Severe Anaemia caused by iron deficiency; vitamin b12 deficiency, cancer or kidney failure can cause pulsatile tinnitus. Pulsatile tinnitus resembles the sound of a heartbeat in the ear. Anaemia causes low blood viscosity, which increases blood flow. Anything that increases blood flow can cause pulsatile tinnitus. Pulsatile tinnitus can be caused by a number of other medical conditions including hyperthyroidism and sounds that are conducted into the middle ear from the carotid artery and jugular vein. This is because they run so close to the inner ear.  If tinnitus is attributed to Anaemia the severity of symptoms can reflect the level of iron deficiency. Once the cause of Anaemia is found and treatment is successful the tinnitus symptoms usually subside.

Common Anaemia Symptoms

• Fatigue
• Weakness
• Rapid Heartbeat
• Breathlessness
• Dizziness or light headedness
• Headache
• Pale Skin
• Feeling faint
• Tinnitus
• Irritability
• Low energy levels
• Weight loss
• Heart palpitations
• Loss of sex drive
• Mental confusion
• Pica
• Restless legs

Anaemia Causes

Iron Deficiency

• Poor diet
• Unbalanced vegetarian diet
• Demands of pregnancy and breastfeeding
• Menstruation
• Blood donation
• Bowel conditions – Crohn’s disease
• Non-steroidal anti-inflammatory drugs
• Endurance sports

Blood Loss

• Gastrointestinal conditions. Haemorrhoids, Gastritis, Stomach Ulcers and Gastrointestinal cancer
• Chronic Kidney Disease
• Menstruation
• Pregnancy
• Accidents and Trauma
• Angiodysplasia
• Inflammatory bowel disease
• Haematuria (blood in your urine)
• Nose bleeds
• Oesophagitis
• Non-steroidal anti-inflammatory drugs

Decreased red blood cell production

• Thalassaemia
• Vitamin B12 Deficiency
• Stem cell and bone marrow problems
• Sickle cell anaemia

Treatment for Anaemia

The main treatment for anaemia is iron supplements in tablet form or eating foods that are rich in iron.

Iron Supplement Side Effects

• Nausea
• Diarrhea
• Upset stomach
• Constipation

Iron Supplements for Meat Eaters

• Beef
• Chicken
• Clams
• Molluscs
• Mussels
• Oysters
• Sardines
• Turkey

Iron Supplements for Vegans and Vegetarians

• Legumes: Soybeans, Lentils, Lima beans, Tofu
• Grains: Brown rice, Oatmeal, Quinoa
• Nuts: Pine, Pistachio, Cashews
• Seeds: Pumpkin, Squash, Sesame
• Dried fruit: Apricots
• Whole grains, Brown rice
• Fortified breakfast cereals
• Green vegetables: Kale, watercress

When taking iron supplements

• The less you eat the better it is absorbed
• Combine non-heme iron foods with Vitamin C to increase absorption
• Take with meals and orange juice
• Keep taking for several months after you are better
• Regular iron check ups
• Drink plenty of fluids

 Question  Is iron deficiency anemia associated with hearing loss in the adult population?
Findings  In this retrospective cohort study of 305 339 young to elderly adults, iron deficiency anemia was positively associated with sensorineural hearing loss and the presence of combined hearing loss.
Meaning  Additional studies to examine how iron supplementation influences hearing status are warranted.

Abstract

Importance  Hearing loss in the US adult population is linked to hospitalization, poorer self-reported health, hypertension, diabetes, and tobacco use. Because iron deficiency anemia (IDA) is a common and easily correctable condition, further understanding of the association between IDA and all types of hearing loss in a population of US adults may help to open new possibilities for early identification and appropriate treatment.
Objective  To evaluate the association between sensorineural hearing loss (SNHL) and conductive hearing loss and IDA in adults aged 21 to 90 years in the United States.
Design, Setting, and Participants  The prevalence of IDA and hearing loss (International Classification of Diseases, Ninth Revision codes 389.1 [SNHL], 389.0 [conductive hearing loss], and 389 [combined hearing loss]) was identified in this retrospective cohort study at the Penn State Milton S. Hershey Medical Center, Hershey, Pennsylvania. Iron deficiency anemia was determined by low hemoglobin and ferritin levels for age and sex in 305 339 adults aged 21 to 90 years. Associations between hearing loss and IDA were evaluated using χ² testing, and logistic regression was used to model the risk of hearing loss among those with IDA. The study was conducted from January 1, 2011, to October 1, 2015.
Main Outcomes and Measures  Hearing loss.
Results  Of 305 339 patients in the study population, 132 551 were men (43.4%); mean (SD) age was 50.1 (18.5) years. There was a 1.6% (n = 4807) prevalence of combined hearing loss and 0.7% (n = 2274) prevalence of IDA. Both SNHL (present in 26 of 2274 individuals [1.1%] with IDA; P = .005) and combined hearing loss (present in 77 [3.4%]; P  < .001) were significantly associated with IDA. Logistic regression analysis confirmed increased odds of SNHL (adjusted odds ratio [OR], 1.82; 95% CI, 1.18-2.66) and combined hearing loss (adjusted OR, 2.41; 95% CI, 1.90-3.01) among adults with IDA, after adjusting for sex.
Conclusions and Relevance  Iron deficiency anemia was associated with SNHL and combined hearing loss in a population of adult patients. Further research is needed to better understand the potential links between IDA and hearing loss and whether screening and treatment of IDA in adults could have clinical implications in patients with hearing loss.

Introduction

In 2014, approximately 15% of adults reported difficulty with hearing, with the highest prevalence among white men.¹ Hearing loss increases with each decade of life, affecting 40% to 66% of adults older than 65 years and 80% of those older than 85 years.^2,3 Risk factors for earlier onset of adult hearing loss include hypertension, diabetes, and tobacco use.^3,4 Sudden sensorineural hearing loss (SNHL) is characterized by a rapid deterioration in hearing function that occurs in less than a 72-hour period. The mechanism is unknown, but a recent study by Chung et al⁵ found a significant association between iron deficiency anemia (IDA) and sudden SNHL (odds ratio [OR], 1.34; 95% CI, 1.11-1.61; P <  .01), which was most prominent in patients younger than 60 years. Iron deficiency anemia is a subset of anemia in which patients exhibit low hemoglobin, serum ferritin, and serum iron levels and increased soluble transferrin receptor levels. In US adults, IDA is usually a result of blood loss and often responds well to reversal of the source of blood loss and oral iron supplementation.⁶

Although the role of iron in the inner ear has not been clearly established, blood supply to this area is highly sensitive to ischemic damage. Sudden SNHL may have a vascular cause potentially exacerbated by IDA as described in a rat model of iron deficiency and sudden SNHL. This study identified defects in the cochlea, including strial atrophy⁷ and reduced spiral ganglion cells, with effects on the stereocilia of the inner and outer hair cells.^7,8 The role of iron in the vasculature and nervous system raises the possibility of its association with other common types of adult hearing loss beyond sudden SNHL. Because IDA is a common and reversible condition, further understanding of the association between IDA and all types of hearing loss in a population of US adults may open new possibilities for treatment. Thus, the objective of this study was to examine the association between IDA and SNHL, conductive hearing loss (CHL), and combined hearing loss among a cohort of adult patients aged 21 to 90 years. Based on previous reports⁵ of sudden SNHL and the mechanical component involved in CHL, the hypothesis was that IDA would demonstrate a stronger association with SNHL compared with CHL.

Methods

Study Population

We performed a retrospective cohort study using data obtained from deidentified electronic medical records from the Penn State Milton S. Hershey Medical Center in Hershey, Pennsylvania. Data were extracted using the National Institutes of Health–supported Informatics for Integrating Biology and the Bedside electronic medical records query tool.^9,10 Patients were included if they were aged 21 to 90 years with at least 1 outpatient, inpatient, or emergency department visit between January 1, 2011, and October 1, 2015. Patients with sickle cell disease (identified as at least 1 International Classification of Diseases, Ninth Revision [ICD-9] code for 282.6) were excluded owing to previous studies linking sickle cell anemia with hearing loss.^11- 17 The study was determined to be exempt by the Pennsylvania State University College of Medicine Institutional Review Board, which also waived the need for patient informed consent because deidentified data were used.

Individuals with IDA were identified based on the presence of at least 1 low serum ferritin (<12.0 ng/mL) value (to convert to picomoles per liter, multiply by 2.247) and 1 low serum hemoglobin value between January 1, 2011, and October 1, 2015. Low hemoglobin values were defined in a previous National Health and Nutritional Examination Survey (NHANES) III study by an expert panel (men: 21-49 years, <13.7 g/dL; 50-69 years, <13.3 g/dL; and ≥70 years, <12.4 g/dL; women: 21-69 years, <12.0 g/dL; ≥70 years, <11.8 g/dL [to convert to grams per liter, multiply by 10]).¹⁸

Patients were identified as having hearing loss if they had at least 1 encounter associated with 1 of the following spectra of ICD-9 codes: 389.0 (CHL), 389.1 (SNHL), or 389 (combined hearing loss). Patients meeting these criteria for hearing loss were categorized as having CHL, SNHL, or combined hearing loss. Combined hearing loss was defined as any combination of CHL, SNHL, deafness, and unspecified hearing loss. Covariates included age (21-69 and ≥70 years) and sex (male and female). Hearing loss–related ICD-9 codes may have been added by a primary care physician, otolaryngologist, or audiologist following a visit with a hearing–related symptom. Formal audiogram testing would not be required for a clinician to select 1 of these codes.

Statistical Analysis

Prevalence of IDA and hearing loss are reported. Two-sided χ² testing was performed and ORs were determined via 2 × 2 contingency tables. In addition, multivariate conditional logistic regression analysis (adjusted for sex) was performed to obtain adjusted ORs and 95% CIs. All statistical testing was performed using R, version 3.2.3 software (The R Project for Statistical Computing).

Results

Demographics

Overall, a total of 305 339 individuals aged 21 to 90 years were identified in the study population. Of these, 132 551 were men (43.4%); mean (SD) age was 50.1 (18.5) years. This cohort was identified as having at least 1 outpatient, inpatient, or emergency department visit at Penn State Hershey Medical Center from 2011 to 2015. The prevalence of IDA was 0.7% (n = 2274). Consistent with published data,¹⁹ IDA was more prevalent in women compared with men (prevalence, 1.1% vs 0.3%; P  < .001). The prevalence of combined hearing loss was 1.6% (n = 4807), and SNHL (0.7%) was more prevalent than CHL (0.2%). Iron deficiency anemia was positively associated with both SNHL (1.1%; P = .005) and the presence of combined hearing loss (3.4%; P < .001) (Table 1).

Association of IDA and Hearing Loss

After adjustment for sex, IDA remained associated with an increased odds of combined hearing loss (adjusted OR, 2.41; 95% CI, 1.90-3.01). Similarly, IDA was associated with increased odds of SNHL (adjusted OR, 1.82; 95% CI, 1.18-2.66) in the adjusted analysis (Table 2). Serum ferritin and hemoglobin are not usually tested unless the diagnosis warrants it; to account for this potential underrepresentation of individuals with IDA, a sensitivity analysis was performed using an IDA prevalence of 3% for women and 1% for men. Overall, similar results were seen, indicating increased odds of both SNHL and combined hearing loss with IDA (eTable in the Supplement).

Discussion

Our study demonstrates increased odds of hearing loss among adults aged 21 to 90 years with IDA. These findings are consistent with those of another observational study in Taiwan that identified an association between IDA and sudden SNHL most prominently in individuals younger than 60 years.⁵ Previous studies^7,8,20- 26 suggest several potential mechanisms by which IDA may affect hearing health; however, it is unknown whether early diagnosis and treatment of IDA could positively affect the overall health status of adults with hearing loss.

The cochlea is highly susceptible to ischemic damage since only the labyrinthine artery supplies blood to this area.²⁷ Iron deficiency anemia has been demonstrated to be a potential risk factor for ischemic stroke due to lower hemoglobin levels leading to impaired oxygen-carrying capacity.^20,21 Individuals with vascular disease have been shown to have a higher risk for developing sudden SNHL.^5,28- 32 Another potential vascular mechanism linking IDA and hearing loss is the increased risk of IDA in patients with reactive thrombocytosis.^22,23 Iron is a regulator of thrombopoiesis, and previous associations between blood loss and thrombocytosis have been established.^33,34 This hypothesis is further substantiated by a case report that demonstrated acute SNHL in a patient with marked thrombocytosis that was reversed after plasmapheresis.³⁵ Iron deficiency results in the degradation of lipid saturase and desaturase, impairing energy production and, consequently, myelin production.²⁴ Damage to the myelin surrounding the auditory nerve impairs conduction velocity resulting in noise-induced hearing loss,²⁵ possibly due to changes in sodium channel density.²⁶

The present study found an association between IDA and hearing loss. Iron deficiency anemia is easily treated with several months of oral iron supplementation.⁶ A study using the NHANES data from 1999-2002 found that individuals with healthier dietary habits were able to detect higher-frequency noises.³⁶ Treatment of IDA will naturally improve anemia and replenish iron stores. Iron deficiency anemia is associated with a large number of related morbidities (eg, fatigue and reduced work capacity), which are also likely to improve with treatment.^37- 56 Additional studies are needed to determine whether there is a link between iron supplementation and hearing status.

Limitations

There are limitations to this analysis that should be considered. The use of laboratory results (ie, serum ferritin and hemoglobin levels) increased the specificity of the IDA definition in our study but reduced the sensitivity. With the wide availability of laboratories not affiliated with our institution and with Informatics for Integrating Biology and the Bedside unable to include data that are not internal, the prevalence of IDA and hearing loss in this study may be falsely reduced. A sensitivity analysis was performed to address this limitation. Using an IDA prevalence of 1% for men and 3% for women, the same analyses were performed. The data remained significant, indicating that although the sensitivity of the analysis is reduced by the present methods, the positive association between IDA and hearing loss remains (eTable in the Supplement). In addition, identifying whether iron deficiency or anemia alone is associated with hearing loss is unable to be accurately performed with this analysis since hemoglobin and serum ferritin are not often tested in the general population. Therefore, distinguishing between iron deficiency, anemia, and IDA would not be definitive.

The prevalence of combined hearing loss, SNHL, and CHL was also lower than has been reported in the literature.³ An analysis using NHANES data from 2001 to 2008 reported a prevalence of 3.2% (95% CI, 1.4%-5.1%) of bilateral and unilateral hearing loss of more than 25 dB among individuals aged 20 to 29 years, increasing with each decade of life with a prevalence of 89.1% (95% CI, 86.1%-92.0%) for those 80 years or older. In contrast, this present investigation was an observational study of health care–seeking adults, and the results may not be generalizable to the rest of the US population.⁵⁷ Patients with hearing loss in this analysis were defined by ICD-9 codes; thus, there are no diagnostic values for comparison. There were likely instances in which hearing loss was not consistently coded due to human error during data entry, neglect to include the ICD-9 code for hearing loss in the patients’ medical records, or exclusion from the query due to billing before January 2011. Similarly, adjusting for potential risk factors, such as smoking status, is unable to be performed in Informatics for Integrating Biology and the Bedside owing to noninclusion in the database. Adjusting for other potential risk factors, such as diabetes and hypertension, is possible with our model, but the results would then be uninterpretable because of the high collinearity between age and these confounding comorbidities.