Hearing loss may be linked to iron deficiency anemia -- a combination of low levels of iron and red blood cells, new research suggests.
The study found that people with iron deficiency anemia have more than twice the rate of hearing loss as people without the blood disorder.
The association between hearing loss and iron deficiency anemia was particularly strong for two types of hearing loss -- one called sensorineural and combined sensorineural and conductive hearing loss.
Sensorineural hearing loss occurs when the inner ear or the nerve pathway from the inner ear to the brain is damaged, according to the American Speech-Language-Hearing Association (ASHA).
Conductive hearing loss is when sounds aren't efficiently conducted from the outer ear to the eardrum or middle ear. Combined hearing loss is a mixture of the two, according to ASHA.
Sensorineural hearing loss is generally considered permanent, ASHA reports. And, that's where this study comes in. If iron deficiency anemia plays a role in hearing loss, it's possible that correcting the condition might lead to improvements in hearing.
But, for now, researchers say it's too soon to tell if that would happen, and they aren't recommending that people with hearing loss get blood tests for anemia.
"There is currently no evidence to confirm that treating iron deficiency anemia will improve hearing health," said study author Kathleen Schieffer. She's a graduate student at the Pennsylvania State University College of Medicine in Hershey, Pa.
The findings only show a possible connection between iron deficiency anemia and hearing loss, she said. They don't prove that one causes the other.
Still, Schieffer said, the study authors want to understand whether treating the blood condition will help improve or prevent hearing loss, particularly since iron deficiency anemia is a common and treatable condition in the United States.
The study authors pointed out that the inner ear is very sensitive to changes in blood supply, so it's possible that the lack of oxygen in the blood of people with iron deficiency anemia might affect the inner ear.
"The part of the inner ear affected by sensorineural hearing loss is supplied by only one artery, which makes it susceptible to damage if low oxygen is present," Schieffer said.
For the new study, the researchers checked diagnoses of hearing loss in more than 300,000 U.S. adults from 2011 to 2015. They were between the ages of 21 and 90, with an average age of 50. Most were women.
"Overall, 1.6 percent of the general population had hearing loss, while 3.4 percent of individuals with iron deficiency anemia had hearing loss," Schieffer said.
When the researchers looked at the type of hearing loss, the overall risk for sensorineural hearing loss in someone with iron deficiency anemia was 82 percent higher than for someone without a blood condition. People with anemia had a 2.4 times greater risk of combined hearing loss than folks without anemia.
Dr. David Haynes, a professor of otolaryngology, neurosurgery, and hearing and speech sciences at Vanderbilt University Medical Center, said "these and other studies should put iron deficiency on the radar as one of the factors that may be contributing to hearing loss. Other studies will be needed to confirm the findings, as in all medical research."
As for why iron deficiency anemia might be connected to hearing loss, ear-nose-and-throat specialist Peter Steyger of Oregon Health & Science University's Oregon Hearing Research Center said several factors could be at play.
"Iron is clearly required for normal functioning of the auditory system, as for many other organs, and too little can result in anemia, the loss of hemoglobin in red blood cells to carry oxygen to the tissues in the body," he said.
Too little iron can also disrupt the workings of cells and even kill them, he said, leading to hearing loss if that happens to hair cells in the inner ear. "Unlike other organs," he said, "once the sensory hair cells in the inner ear are damaged and die, they cannot be restored to restore auditory function."
"A healthy well-balanced diet that meets the daily recommended intake of vitamins and other nutrients is crucial for everyone's general physical well-being, as well as for optimal hearing health," he said.
The study was published Dec. 29 in the journal JAMA Otolaryngology-Head & Neck Surgery.