MONDAY, Feb. 14, 2011 (HealthDay News) -- Adults who experience hearing loss may face a higher risk of dementia and perhaps Alzheimer's disease than those who don't suffer hearing loss, new research suggests.
And the greater the loss, the greater the risk, the study suggested.
"This work suggests that there is a strong predictive association between hearing loss as an adult and the likelihood of developing cognitive decline with aging," said study lead author Dr. Luigi Ferrucci, chief of the U.S. National Institute on Aging's Longitudinal Studies Section, as well as director of the Baltimore Longitudinal Study of Aging.
Ferrucci and his colleagues report their findings in the February issue of the journal Archives of Neurology.
The authors noted that by the middle of the century, about 100 million men and women worldwide (about one in 85) will be affected by dementia.
The researchers' investigation into the potential association between hearing loss and dementia focused on 639 men and women between the ages of 36 and 90, none of whom had dementia at the start of the study in 1990.
Cognitive and hearing tests were conducted over a four-year period, followed by patient tracking through 2008 (for an average of about 12 years) to monitor for signs of dementia and/or Alzheimer's.
The researchers noted that 125 study participants were diagnosed with "mild" hearing loss, while another 53 had "moderate" loss, and six had "severe" loss.
Ultimately, 58 patients were diagnosed with dementia, of whom 37 had Alzheimer's disease.
By cross-referencing their data, the researchers found that mild hearing loss was linked to a slight increase in dementia risk, but the risk increased noticeably among those with moderate and severe hearing loss.
For participants 60 and older, more than 36 percent of dementia risk was linked to hearing loss, the study said.
The worse the hearing loss, the worse the risk for Alzheimer's as well. For every additional loss of 10 decibels of hearing capacity, Alzheimer's risk appeared to go up by 20 percent, the researchers said.
The authors suggested that if further studies confirm the findings, this could lead to the development of new strategies to try to reduce dementia risk. For example, the finding theoretically suggests that efforts to correct hearing loss by means of hearing aids and surgery could potentially cut back on dementia risk.
"But as a scientist I cannot yet say that curing hearing loss will prevent dementia," Ferrucci said. "We have now opened a window on this association. But there is still a lot of work to be done before we can be sure there is actually a causal relationship."
Dr. Richard B. Lipton, vice chair of neurology at Albert Einstein College of Medicine in New York City, called the new study an "interesting" exploration that is predicated on "the widespread notion that chronological age may not be the best measure of biological age."
"Some people have suggested that the most powerful risk factor that we know of for Alzheimer's is age itself," he noted. "The older you are the more likely you are to develop the disease. And we know that risk doubles every five years after the age of 65," Lipton added.
"But some 90-year-olds are in nursing homes, while others are on the golf course. So here we have the notion that hearing loss may be a kind of biological, rather than chronological, measure of aging. In other words, an indication that someone is not actually aging all that well," he said.
"Another idea is that hearing loss might result from damage to nerve cells," Lipton added. "That means damage to the hearing organ and inner ear structure called the cochlea, and the hair cells that pick up the pattern of vibration that the sound produces in the ear. And if there's damage to the neurons that mediate hearing, that may be a kind of marker for similar damage to nerve cells involved in memory and higher cognition," he explained.
"And then a third possibility is that there's a lot of evidence that hearing loss is very socially isolating, just as there's a lot of evidence that cognitive engagement protects against dementia. And that would mean that the loss of cognitive stimulation could itself contribute to the risk for Alzheimer's," Lipton said.
For more on risk factors for Alzheimer's disease, visit the Alzheimer's Association.