Age-related hearing loss, a common problem among the elderly, might be related to inadequate levels of folic acid, European researchers report.

The researchers found that people who took a folic acid supplement had less decline in hearing low-frequency sounds over time, compared with people who didn't take the supplement.

Results of the study, led by Jane Durga, of the Cognitive Sciences Group, Nutrition & Health Department at the Nestle Research Center in Lausanne, Switzerland, are published in the Jan. 2 issue of the Annals of Internal Medicine.

The researchers randomly assigned 728 older Dutch men and women, who showed signs of age-related hearing loss and low folate levels, to receive either 800 grams of a folic acid supplement or a placebo daily for three years.

Durga's team chose to conduct the study in the Netherlands because, unlike the United States, the Netherlands does not fortify its food with folic acid, a B vitamin also known as folate. Folate levels in study participants were about half those found in Americans. In the United States, many foods contain supplemental folic acid because of its benefits in protecting against birth defects.

At the end of the trial, the researchers found that the ability to hear low-frequency sound did not decrease significantly among those taking folic acid supplements. However, there was no slowing in the decline in hearing high frequencies in either group.

The thresholds of the low frequencies increased by 1.0 decibel in the folic acid group and by 1.7 decibels in the placebo group, the researchers said.

"Folic acid supplementation slowed the decline in hearing of the speech frequencies associated with aging in a population from a country without folic acid fortification of food," the researchers wrote. "The effect requires confirmation, especially in populations from countries with folic acid fortification programs."

But Robert W. Sweetow, director of audiology at the University of California, San Francisco, Medical Center, called the results "clinically insignificant."

"I think that their conclusion that folic acid is actually slowing down the progression of age-related hearing loss is a stretch," Sweetow said. "I would hate to say to patients, 'You take folic acid and the progression of your hearing loss is going to slow down.'"

Another expert questioned the significance of the finding.

"The effect is on low frequency hearing, but most older folks have a problem with high frequency hearing," said Dr. Hinrich Staecker, an associate professor in the department of otolaryngology-head & neck surgery at the University of Kansas Medical Center.

Staecker also noted that the study authors didn't look at the ability of the participants to hear speech clearly. "It's easier to make stuff louder, but it's not easy to make stuff clearer," he said.

Dr. Peter M. Rabinowitz, an associate professor of medicine at the Yale University School of Medicine, said, "The investigators' finding that low-frequency, but not high frequency, hearing loss was reduced in the folate supplementation group is somewhat surprising, since age-related hearing loss usually affects the higher frequencies of hearing first and to a greater degree."

Clearly, much is not known about nutrition and hearing, Rabinowitz said. For example, other studies have suggested that genetic differences in the metabolism of folate may affect how someone responds to supplementation, including the effect of folate on hearing loss, he said.

"While neither this study nor the current state of medical knowledge provide adequate evidence for recommending particular supplements to prevent hearing loss, this study provides additional evidence of the importance of adequate nutrition in older adults, as well as the potential for future discoveries of how to slow the aging process of the hearing system," Rabinowitz said.