While other studies previously have found the same link, many of them looked only at older adults or at specific regions or ethnicities, and results have been mixed, the researchers pointed out.
In the new study, as hearing declined, the percentage of depressed adults increased -- from about 5 percent in those who had no hearing problems to more than 11 percent in those who did.
"We found a significant association between hearing impairment and moderate to severe depression," said study author Dr. Chuan-Ming Li, a researcher at the U.S. National Institute on Deafness and Other Communication Disorders. "The cause-and-effect relationship is unknown," Li said, citing a need for further studies.
The study was published online March 6 in JAMA Otolaryngology--Head & Neck Surgery.
The new findings make sense, according to two experts in the field who reviewed the study conclusions.
"It is not surprising to me that they would be more likely to be depressed," said James Firman, president and CEO of the National Council on Aging. "People with hearing loss, especially those who don't use hearing aids, find it more difficult to communicate with other people, whether in family situations, social gatherings or at work."
Experts who care for those with hearing loss have long noticed the link, said Robert Frisina, director of the Global Center for Hearing & Speech Research at the University of South Florida, in Tampa. "When they come in [to see about their hearing], they mention this," he said.
Even so, Frisina noted, the study is valuable because it adds solid data to the anecdotal information.
For the new study, the researchers looked at data from the U.S. National Health and Nutrition Examination Survey, including more than 18,000 adults aged 18 and older. The younger people self-reported on their hearing status, while hearing tests were given to those 70 and older. All participants filled out a questionnaire designed to reveal depression.
As hearing loss became worse, the depression did, too, except among those who were deaf. These adults, Frisina said, may be accustomed to coping with the loss.
Hearing loss was linked with an increased risk of depression in adults of all ages, but was most pronounced in the respondents aged 18 to 69, the investigators found. Women had higher rates of depression than men did.
Among those 70 and older, no link was found between self-reported hearing loss and depression. However, a link was found for women in this age group if the hearing test found a hearing loss.
That could be because women start to lose hearing in higher frequencies after age 65, and those frequencies are crucial to understand speech in noisy environments, the study authors noted.
While it is difficult to sort out cause and effect, Frisina said, the researchers did take into account other conditions that could affect hearing, including trouble seeing, and the link held. "It's probably a pretty strong link," he added.
Those who think they are having trouble hearing should seek help, he suggested. Often, family and friends notice the loss first. "If you have hearing loss, you need to go to an audiologist and otolaryngologist and have it diagnosed properly, and then you can look at treatment options," Frisina said.
To learn more about hearing loss, visit the U.S. National Institutes of Health.