July 18, 2011 -- Adolescents who are exposed to secondhand tobacco smoke have nearly double the risk of hearing loss than those who are not exposed, according to a new study.
The researchers say the study is the first to show a connection between hearing loss in adolescents and exposure to tobacco smoke. It involved more than 1,500 people ages 12 to 19 nationwide.
The young people were first evaluated in their homes and then given extensive hearing tests and evaluation of blood samples to determine levels of the nicotine chemical cotinine in their blood.
The findings are published in the July issue of Archives of Otolaryngology -- Head and Neck Surgery.
Reducing Exposure to Secondhand Smoke
Researchers say the teens exposed to secondhand smoke, as measured by cotinine, were more likely to have sensorineural hearing loss, a condition most often caused by problems with the cochlea, a snail-shaped hearing organ in the inner ear.
"It's the type of hearing loss that usually tends to occur as one gets older or among children born with congenital deafness," study researcher Michael Weitzman, MD, of the New York University School of Medicine, says in a news release.
Another study researcher Anil Lalwani, MD, also a professor at the New York University School of Medicine, says the results strongly suggest that more needs to be done to reduce childhood exposure to tobacco, both in their homes and at public places.
Also, children may need to be screened more regularly for hearing problems because few realized they have hearing difficulties. "More than half of all children in the U.S. are exposed to secondhand smoke, so our finding that it can lead to hearing loss in teenagers has huge public health implications," Lalwani says.
The study shows that teens exposed to smoke performed worse across every sound frequency tested, especially mid-to-high frequencies that are important for understanding speech.
Also, teenagers with higher cotinine levels, indicating more exposure to tobacco smoke, were more likely to have one-sided or unilateral low-frequency hearing loss.
The researchers conclude that overall, their findings indicate that tobacco smoke is "independently associated with an almost two-fold increase in the risk of hearing loss among adolescents."
Unaware of Hearing Loss
More than 80% of the affected teens in the study were not aware they had any hearing problem, and Lalwani says milder hearing loss is not always noticeable. Therefore, he says, just asking a person whether they think they have hearing loss is may not be a sufficient way to determine if they do.
Weitzman says the mild hearing loss may have several causes, including a detrimental effect on the blood supply to the inner ear. All infants born in the U.S. are required to be screened for hearing loss, but Lalwani says there are no guidelines for testing a child's hearing past the early school years. Children exposed to secondhand smoke, he says, "need to be regularly screened."
The study says more than 50% of children in the U.S. are exposed to secondhand smoke.
The researchers say the rate of hearing loss appeared to be cumulative, increasing with the level of cotinine detected in the blood.
The researchers say their finding "may have profound implications in light of the high exposure rates among adolescents" in the U.S. Future research, they say, needs to be done because of the adverse effects caused by hearing loss in children, including poorer academic performance and social development.