Diabetes has already been tied to an increased risk of kidney and cardiovascular troubles, nerve damage and vision loss, and now a new study finds diabetics to be more than twice as likely as those without the disease to have hearing impairment.

In a review of past research on the question, scientists in Japan also found that younger diabetics were at even higher risk than older adults - though they cannot explain why, and experts caution that this kind of study does not prove that diabetes is directly responsible for the greater hearing loss rates.

“It doesn’t definitively answer the question, but it continues to raise an important point that patients might ask about,” said Dr. Steven Smith, diabetes specialist at the Mayo Clinic in Rochester, Minnesota.

It’s also not the first time researchers have found a link between diabetes and hearing loss.

In 2008, researchers from the U.S. National Institutes of Health (NIH) saw similar patterns in a sample of more than 11,000 people. In that study, people with diabetes were twice as likely to have hearing loss as those without the condition.

Generally, hearing loss is defined as having trouble understanding what people are saying in a hushed voice, and missing some words at a regular volume.

The American Diabetes Association estimates there are currently about 16 million people living in the U.S. with diabetes, and NIH says about 36 million Americans report some level of hearing loss.

It’s thought that high blood sugar levels brought on by diabetes may lead to hearing loss by damaging blood vessels in the ears, according to Chika Horikawa, the study’s lead author from Niigata University Faculty of Medicine in Japan, and colleagues.

They collected information from 13 previous studies examining the link between diabetes and hearing loss and published between 1977 and 2011. Together, the data covered 7,377 diabetics and 12,817 people without the condition.

Overall, Horikawa’s team found that diabetics were 2.15 times as likely as people without the disease to have hearing loss. But when the results were broken down by age, people under age 60 had 2.61 times the risk while people over 60 had 1.58 times higher risk.

The researchers, whose findings appear in the Journal of Clinical Endocrinology and Metabolism, note that future studies that take more factors into account, such as age and noisy environments, are needed to clarify the link between diabetes and hearing loss.

Still, Horikawa told Reuters Health in an email, people should recognize that diabetics may be at risk for hearing loss based on their results.

“Furthermore, these results propose that diabetic patients are screened for hearing impairment from (an) earlier age compared with non-diabetics,” said Horikawa, adding that hearing loss has also been linked to an increased risk of depression and dementia.

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SOURCE: Journal of Clinical Endocrinology and Metabolism, online November 12, 2012.

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