About 85 percent of those with hearing loss are untreated, Dr. Lin said. For older adults alone, this increased health care costs by 46 percent over a period of 10 years, compared with costs incurred by those without hearing loss, the authors reported in November in JAMA Otolaryngology Head and Neck Surgery.

One of the authors, Jennifer A. Deal, an epidemiologist and gerontologist at the Johns Hopkins Bloomberg School of Public Health, said that while “hearing loss itself is not very expensive, the effect of hearing loss on everything else is expensive.”

Unfortunately, people tend to wait much too long to get their hearing tested and treated with hearing aids, and the longer they wait, the harder it is to treat hearing loss, Dr. Lin told me.

Age-related hearing loss comes on really slowly, making it harder for people to know when to take it seriously, he said. He cited two good clues to when to get your hearing tested: Family members or close friends say you should, or you notice that you often mishear or don’t know what others are saying.

But even when people are tested and spend thousands of dollars to purchase needed hearing aids, the devices often sit in a drawer. People may complain that the sound quality is poor, too static-y or otherwise annoying, and that the aids merely amplify all sound, making it still hard to hear in a noisy environment. All aids are not created equal, Dr. Lin said, and even expensive, properly fitted aids can require multiple adjustments. Some people give up too readily to get the best results.

“Unrealistic expectations are a big part of this problem,” Dr. Lin said. “It’s not like putting on a pair of glasses that immediately enables you to see clearly,” he said. “Hearing loss is not fixed as easily as eyesight. The brain needs time — a good month or two — to adjust to hearing aids. And the earlier hearing loss is treated, the easier it is for the brain to adapt.”

The new studies give ample cause for taking hearing loss seriously. Consider, for example, the link to dementia. People who can’t hear well often become socially isolated and deprived of stimuli that keep the brain cognitively engaged. As input lessens, so does brain function.