Exposed adolescents were 1.83 times more likely to experience low-frequency hearing loss than those who had no exposure, according to Dr. Anil K. Lalwani and colleagues from New York University in New York City.
And the greatest risk for hearing loss -- a 2.72-fold increase -- was in those with the highest levels of exposure as determined by serum cotinine levels, Lalwani's group reported in the July Archives of Otolaryngology-Head & Neck Surgery.
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The list of potentially harmful outcomes associated with exposure to secondhand smoke continues to grow, from low birth weight to behavioral and cognitive problems and respiratory tract infections -- and more than half of U.S. children are exposed.
In the first study to examine secondhand smoke exposure and sensorineural hearing loss in young people, the investigators analyzed cross-sectional data from the 2005-2006 National Health and Nutrition Examination Survey (NHANES).
They identified 1,533 nonsmokers ages 12 to 19 who had undergone audiometric testing and whose serum cotinine levels had been measured.
Low-frequency sensorineural hearing loss was defined as a pure-tone level above 15 dB for 0.5, 1, and 2 kHz, while high-frequency loss was a level above 15 dB for 3, 4, 6, and 8 kHz.
Overall rates of hearing loss ranged from 3.68 percent for bilateral high-frequency hearing loss to 9.55 percent for unilateral low-frequency hearing loss.
Yet only 18.43 percent of the teens with these forms of hearing loss were aware of the problem.
Other factors associated with hearing loss included a history of eczema, black race, and having been cared for in a neonatal intensive care unit.
When participants were divided into quartiles by level of serum cotinine, the prevalence increased from 7.53 percent in nonexposed adolescents to 17.05 percent of those with the highest level of this marker of tobacco exposure.
The researchers noted that the link of secondhand smoke exposure with elevated thresholds ranging from 0.5 kHz to 8 kHz suggests "that the injury to the inner ear is global."
In addition, the unilateral hearing loss is probably an early phase of ocular damage that is likely to progress in severity, they cautioned.
The elevated thresholds at 2, 3, and 4 kHz were particularly important, according to Lalwani and colleagues.
"These mid-to-high frequencies are critical for hearing in humans and are responsible for the clarity of hearing that allows us to discriminate between similar sounding words," they observed.
Possible mechanisms by which secondhand smoke could result in auditory damage include effects on the vasculature of the inner ear and injury from nicotine or other components of the smoke.
Hearing loss in young children has been shown to interfere with not only speech and language development, but also cognitive function, academic progress, and social interaction.
But newborns and young children are routinely screened for hearing difficulties, while adolescents are not.
The findings of this study suggest that teens who are exposed to secondhand smoke should have their hearing tested, and parents and caretakers should be made aware of the auditory hazards of their smoking.
Limitations of the study include its use of cross-sectional data which doesn't allow assignment of causation, lack of information on duration and sources of secondhand smoke exposure -- including prenatal exposure -- and absence of data on other factors such as exposure to loud noises.
The researchers also were unable to rule out the possibility that some of the participants had conductive, rather than sensorineural, hearing loss.
They concluded, "Future studies need to investigate the adverse consequences of this early hearing loss on social development, academic performance, behavioral and cognitive function, and public health costs."