Hearing loss is twice as common in people with diabetes compared to those who do not have the disease, a new study has found.
The findings of the study, conducted by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), suggest that people with diabetes should consider having their hearing tested.
"Hearing loss may be an under-recognized complication of diabetes. As diabetes becomes more common, the disease may become a more significant contributor to hearing loss," said senior author Catherine Cowie, Ph.D., of NIDDK.
"Our study found a strong and consistent link between hearing impairment and diabetes using a number of different outcomes," she added.
For the study, researchers analysed the results of hearing tests given to a nationally representative sample of adults in the United States.
Half of the 11,405 survey participants aged 20 to 69 were randomly assigned to have their hearing tested, and nearly 90 percent of them completed the hearing exam and the diabetes questionnaire.
The hearing test, called pure tone audiometry, measures hearing sensitivity across a range of sound frequencies.
The test measured participants' ability to hear low, middle, and high frequency sounds in both ears.
"Using the data from the hearing tests, we measured hearing impairment in eight different ways. Also, participants responded to questions about hearing loss in the questionnaire, which asked whether they had a little trouble hearing, a lot of trouble hearing, or were deaf without a hearing aid," Cowie said.
In addition, 2,259 of the participants who received hearing tests were randomly assigned to have their blood glucose tested after an overnight fast.
The link between diabetes and hearing loss was evident across all frequencies, with a stronger association in the high frequency range.
Mild or greater hearing impairment of low- or mid-frequency sounds in the worse ear was about 21 percent in 399 adults with diabetes as compared to about 9 percent in 4,741 adults without diabetes.
For high frequency sounds, mild or greater hearing impairment in the worse ear was 54 percent in those with diabetes as compared to 32 percent in those who did not have the disease.
Researchers also found that adults with pre-diabetes, whose blood glucose was higher than normal but not high enough for a diabetes diagnosis, had a 30 percent higher rate of hearing loss as compared to those with normal blood sugar tested after an overnight fast.
Co-author Howard Hoffman, an epidemiologist at NIDCD said: "This is the first study of a nationally representative sample of working age adults, 20 to 69 years old, and we found an association between diabetes and hearing impairment evident as early as ages 30 to 40."
The researchers suggest that diabetes may lead to hearing loss by damaging the nerves and blood vessels of the inner ear. Autopsy studies of diabetes patients have shown evidence of such damage.
The study is published online June 17, 2008, in the Annals of Internal Medicine.