The study does not prove cause and effect. But it's a good idea for diabetes patients to be screened routinely for hearing loss, just as they are for eye and kidney problems, says researcher Hirohito Sone, MD, PHD, of Tsukuba University Hospital Mito Medical Center in Ibaraki, Japan.
Smaller studies have linked diabetes to hearing loss, "but no one knew just how much higher their risk is, compared with people without diabetes," he tells WebMD.
So Japanese researchers pooled the results of 13 studies involving nearly 8,800 people with hearing impairment, of whom more than 1,000 had diabetes, and 23,839 people without hearing impairment, of whom nearly 2,500 had diabetes. The large numbers allowed them to observe trends that aren't apparent in smaller studies.
The findings were presented here at the annual meeting of the American Diabetes Association.
Blood Vessel Damage
It’s unknown why hearing loss is more common among people with diabetes, but most researchers believe that damage to the blood vessels is the main culprit, according to Pamela D. Parker, MD, of the A.T. Still University School of Osteopathic Medicine in Mesa, Ariz. She has studied the link between hearing loss and diabetes for years but was not involved with the new study.
Researchers believe that over time, the high blood sugar levels that characterize diabetes may damage the small blood vessels of the inner ear, making it harder to hear. Autopsy studies of diabetes patients have shown evidence of such damage.
Nearly 26 million Americans have diabetes and about 34.5 million Americans have some type of hearing loss, according to the American Diabetes Association.
A 2008 study showed that 54% of people with diabetes had at least mild hearing loss in their ability to hear high-frequency tones, compared with 32% of those with no history of diabetes. And 21% of participants with diabetes had at least mild hearing loss in their ability to hear low-to-mid frequency tones, compared with 9% of those without diabetes.
The new study suggests that people with diabetes are 2.3 times more likely to have mild hearing loss, defined as having trouble hearing words spoken in a normal voice from more than 3 feet away.
These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.