Meanwhile, the new findings on cognitive losses linked to subclinical hearing loss, gleaned from among 6,451 people age 50 or older, suggest that any degree of hearing loss can take a toll.
Currently, the sound level of 25 decibels — the ability to hear a whisper — is used to define the border between normal hearing and mild hearing loss in adults.
But this threshold is really arbitrary. The lead author of the study, Dr. Justin S. Golub, otolaryngologist and researcher at Columbia University Irving Medical Center, and his colleagues found that hearing loss is on a continuum that starts with “perfect” hearing at zero decibels (the sound level of a pin drop), with measurable cognitive deficits occurring with every additional loss above zero.
In fact, the researchers demonstrated that the biggest drop in cognitive ability occurs at the slightest level of hearing loss — a decline from zero to the “normal” level of 25 decibels, with smaller cognitive losses occurring when hearing deficits rise from 25 to 50 decibels.
“This doesn’t mean we should be fitting people with hearing aids when the softest sound they can hear is 25 decibels,” Dr. Golub said in an interview. After all, getting people with far more advanced hearing loss to use hearing aids is already an enormous challenge. As Dr. Golub noted, “Currently only 25 percent of people over 80 wear hearing aids, yet 80 percent of them have significant hearing loss” that might be greatly improved with aids.
The new findings linking cognitive decline to even minimal hearing loss suggest that we could do a lot to protect our brains if we protect our hearing. The fact that measurable cognitive losses occur at hearing levels below 25 decibels, and that cognition gradually worsens as hearing declines, suggests that protecting against hearing loss should start in childhood.
“In people with very good hearing, we need to be aware of how early changes in hearing affect the brain,” said Dr. Frank Lin, director of the Cochlear Center for Hearing and Public Health at the Johns Hopkins Bloomberg School of Public Health. “Without a doubt, the most important measure to preserve hearing is protection against noise.”