At 100, Ann Stenzel is feisty and sharp, in part because her hearing aids, which she has used for a decade, keep her in touch with the world around her.
She likes to spend her mornings reading the newspaper in the sunny lobby of her Granite Bay, Calif., seniors' residence center, where she strikes up conversations with fellow residents.
"I don't want to miss anything," said Stenzel. "But half the people here can't hear. ... They'll say it makes them feel old to get hearing aids. But wearing them makes me feel young."
The incidence of hearing loss, one of the hidden impairments of old age, has doubled in the past three decades. It affects 26.7 million Americans 50 and older, including four out of five people above age 80.
Despite its prevalence among older adults, hearing loss remains largely untreated: Only 14 percent of seniors who need hearing devices have them.
As a result, many older adults are unnecessarily missing out on the life that's swirling around them, unheard and unacknowledged.
Researchers say it's possible they're putting their health at risk, too. A recent Johns Hopkins University study suggests that hearing loss can upset fragile seniors' sense of balance, tripling their chances of a fall.
And diminished hearing affects quality of life. It can lead to early retirement and less independence for people in their 50s and 60s -- and for older seniors, inability to hear and communicate can launch them into a downward spiral of isolation and self-neglect.
"If hearing loss is mild, people are still able to be involved in the environment around them and take part in social activities," said Kaiser Permanente audiologist Robert Spacagna. "If it's greater, they can't sit in a restaurant and hear separate conversations. They can't communicate. It's frustrating because it's so much work for them.
"Over time, they become isolated and give up their normal activities. They stay in their own little world and forget the other world."
Some research suggests that severe hearing loss goes hand in hand with a risk of dementia.
"As someone becomes increasingly hearing impaired, it can be difficult separating out the confusion caused by their isolation and inability to hear, on the one hand, and the confusion caused by a brain disorder," said Elizabeth Edgerly, chief program officer of the Alzheimer's Association of Northern California.
Medications, including some antibiotics and diuretics, also have been found to cause temporary or permanent hearing loss. So have Viagra and Cialis, according to the U.S. Food and Drug Administration.
But in most cases, age-related hearing loss is easily correctable through the use of properly fitted hearing aids, which these days are tiny digital devices that can be fine-tuned to accommodate different sound environments.
So why do such a small number of hearing-impaired older adults -- only one of every seven -- use hearing aids?
For one thing, the technology can overwhelm older people, who tend to be a few decades removed from the Bluetooth-wearing, ear bud-loving generations for whom a hearing aid might be just another high-tech device to put in the ear.
Some seniors are too proud to admit they need assistance with their hearing, experts say -- and others are too vain to wear hearing aids.
The third major reason is the price tag. Medicare doesn't routinely cover the cost of hearing aids, which can run from $1,000 to $4,000 per ear, nor do most private medical plans.
"It's an investment," said Jane Rupp, a registered nurse whose father wears hearing aids. "But from the perspective of spouses and families, it makes communicating with your loved ones easier."