March 14 (UPI) -- Smokers had a 60 percent increased risk of hearing loss compared to people who have never smoked, according to an eight-year study in Japan.
While quitting can lessen the increased risk for hearing loss, researchers said smoking has a clear effect on the risk for hearing loss in their study of current, former and never smokers, which was published Wednesday in the journal Nicotine & Tobacco Research.
More than 5 percent of the world's population has disabling hearing loss, according to the World Health Organization.
"To the best of our knowledge, our study is the largest to date investigating the association between smoking and incident hearing loss," researchers wrote in the study. "Quitting smoking virtually eliminates the excess risk of hearing loss, even among quitters with short duration of cessation."
A total of 50,195 workers aged 20 to 64 years old and free of hearing loss were examined at the beginning of the eight-year study period. Researchers analyzed annual health checkups, including audio testing performed by a technician and a health-related lifestyle questionnaire.
During the followup period, 3,532 individuals developed high-frequency hearing loss and 1,575 developed low-frequency hearing loss.
The researchers found a 60 percent increase in risk for current smokers to lose high-frequency hearing and 20 percent increased risk to lose low-frequency hearing. For former smokers, the risk declined over time as they still had a 20 percent increased risk for losing high-frequency hearing, but no increased risk for losing low-frequency hearing.
In the analysis, they found a decline in risk of hearing loss after quitting smoking, even among those who had stopped for less than five years. The risk of high- and low-frequency hearing loss was also affected by the number of cigarettes smoked per day.
"With a large sample size, long follow-up period, and objective assessment of hearing loss, our study provides strong evidence that smoking is an independent risk factor of hearing loss," Dr. Huanhuan Hu, a researcher at Japan's National Center for Global Health and Medicine, said in a press release. "These results provide strong evidence to support that smoking is a causal factor for hearing loss and emphasize the need for tobacco control to prevent or delay the development of hearing loss."