Cause of declines difficult to pinpoint

By Laura Sanders

Web edition: January 21, 2013
Print edition: February 23, 2013; Vol.183 #4 (p. 13)

Older people with hearing loss may suffer faster rates of mental decline. People who have hearing trouble suffered meaningful impairments in memory, attention and learning about three years earlier than people with normal hearing, a study published online January 21 in JAMA Internal Medicine reveals. 

The finding bolsters the idea that hearing loss can have serious consequences for the brain, says Patricia Tun of Brandeis University in Waltham, Mass., who studies aging. “I’m hoping it will be a real wake-up call in terms of realizing the importance of hearing.”

Compared with other senses, hearing is often overlooked, Tun says. “We are made to interact with language and to listen to each other, and it can have damaging effects if we don’t.”

Frank Lin of Johns Hopkins School of Medicine and colleagues tested the hearing of 1,984 older adults. Most of the participants, who averaged 77 years old, showed some hearing loss — 1,162 volunteers had trouble hearing noises of less than 25 decibels, comparable to a whisper or rustling leaves. The volunteers’ deficits reflect the hearing loss in the general population: Over half of people older than 70 have trouble hearing.

Over the next six years, these participants underwent mental evaluations that measured factors such as short-term memory, attention and the ability to quickly match numbers to symbols. Everybody got worse at the tasks as time wore on, but people with hearing loss had an especially sharp decline, the team found. On average, a substantial drop in performance would come about three years earlier to people with hearing loss.

Lin cautions that the study has found an association between hearing loss and mental abilities; the researchers can’t conclude that hearing loss directly causes the decline. Yet more and more studies are turning up ways that diminished hearing could damage the brain. A person who can’t hear well might avoid social situations, and isolation is known to be bad for the brain. “You gradually become more socially withdrawn,” Lin says. “Social isolation is a major, major factor for dementia and cognitive decline.”

Other studies suggest that when people struggle to interpret and decode words, their brains divert energy away from other tasks, such as memory. Audiologist and psychologist Kathy Pichora-Fuller says that this brain drain happens to everyone, even people without hearing loss. Studies have shown that people are worse at remembering things when they’re in a noisy room, for instance. People with hearing loss may be constantly diverting a large swath of their brainpower, leaving less for other mental tasks, says Pichora-Fuller, of the University of Toronto Mississauga.

More studies are needed to explore exactly how hearing loss is related to mental decline. Lin and his colleagues hope to study whether improvements in hearing brought about by hearing aids or other treatments translate to improvements in mental functioning. “The ultimate question is, can we do anything about it?” he says. “And we honestly just don’t know at this point.”