Newswise--A new review of existing research says there is little evidence to support mandatory hearing-loss prevention programs at the workplace.

Workers could simply wear earplugs and other devices that protect hearing, but even those are not always effective, the review authors found.

In the big picture, "We still rely too much on hearing protection, which is not sufficient," says review lead author Jos Verbeek, a researcher at the Finnish Institute of Occupational Health in Kuopio, Finland.

An estimated nine million American workers experience exposure to high levels of noise at the workplace. People who work in construction, manufacturing and mining jobs are at especially high risk of losing their hearing.

"It's a very common workplace injury and it's very invisible," says Deanna Meinke, an associate professor of audiology at the University of Northern Colorado. "It takes a while for it to get bad enough for people to pay attention." She has no affiliation with the review.

Verbeek and colleagues searched for studies that examined strategies to prevent hearing loss in the workplace. They found 21 studies that they deemed worthy of inclusion in the review.

The review appears in the latest issue of The Cochrane Library, which is a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.

Only one study looked at workplaces--in this case, U.S. coalmines--that directly reduced exposure to noise because of legislation. It found that the noise level fell, but the review authors reported that the quality of the study is low.

Fourteen studies with 75,672 participants looked at prevention programs, such as noise monitoring, and another six with 169 participants examined specific hearing-protection devices like earplugs.

Studies that examined prevention programs had mixed results. Some studies showed that workers still had a three-fold risk of hearing loss compared to workers not exposed to noise, in spite of a prevention program.

Other studies deemed to be of lower quality showed no difference in risk of hearing loss among those with or without protection devices.

Why don't devices like earplugs and earmuffs work well? "It is difficult to wear hearing protection," Verbeek says. "In addition, if you wear plugs you have to be properly instructed, because if you don't insert them properly there is no protection."

One problem is that some employers "hand out inexpensive, one-size-fits-all earplugs," says Meinke, the Colorado professor. "You wouldn't want me to hand out one pair of work boots for everyone to wear, but some think we can do that with earplugs."

Meinke cautioned, however, that it is difficult to study hearing loss in the workplace. For one thing, the gold standard of research--comparing a group of people who use hearing protection to a group that does not--can be unethical if it means some workers are unprotected, she said.

It is also hard to tell how people's lives outside the workplace affect their hearing, she said. "You could have the best hearing-loss prevention program in the world, but if it doesn't carry on in the outside world, it won't look like it works."

What to do? Although they found little evidence that legislation is effective, the review authors call for more laws to protect workers along with "better implementation and reinforcement."

They also write that the best approach is to reduce exposure to noise, although that can be the most expensive strategy of all. "Companies make very little effort to reduce their noise exposure unless it serves another purpose," says Dr. William Daniell, associate professor at the department of environmental and occupational health sciences at the University of Washington.

Enclosures around noisy machines are one solution. Proper maintenance of the machines can help too, as can simple measures like soundproofing rooms to prevent echoes.

These are better solutions than buying earplugs for employees, he says.

"The problem of doing [hearing loss prevention] at the level of the person is that every person has to do it right all the time for it to work," he says. "With noise control, you solve the problem for everybody, and you don't have to depend on human nature."

For more information: http://www.cochrane.org