Hearing Loss in Children Linked to Secondhand Smoke Exposure, New Study Finds

A smoker stubbs out a cigarette outside a shopping mall in Hong Kong on June 27, 2009. Laurent Fievet/AFP/Getting Images

Sometimes the effects of secondhand smoke aren't overtly noticeable, but still have a significant effect on a child's life. New research from Japan has revealed that exposure to smoking, both in utero and in the first few months of a child's life, is associated with higher prevalence of hearing impairment.

The study, published online in Paediatric and Perinatal Epidemiology, studied data on 50,734 children who were born between 2004 and 2010. The researchers were most interested in the children's hearing health at age three. Of the children, 3.8 percent were exposed to smoke only during their mothers' pregnancies, 15.2 percent were exposed only by their mother's past smoking habits, 3.9 percent were exposed only to secondhand smoke at four months old, and 0.9 percent were exposed to tobacco smoke both during pregnancy and at four months. The children's hearing was tested in a whispered hearing test and parents smoking was measured by a questionnaire.

By age three, 4.6 percent of children had a type of hearing impairment. Results revealed a correlation between exposure to cigarette smoke and hearing impairment in the three year olds. Children exposed to only their mothers' past smoking had a 26 percent increased risk of hearing impairment. Those exposed to only secondhand smoke at four months had a 30 percent increased risk. However, those whose mothers smoked during their pregnancy had a 68 percent increased risk of hearing impairment.

Although the study cannot prove that cigarette smoke exposure was the direct cause of the children's hearing impairment, the researchers did note that preventing this exposure was a clear way to reduce the children's risk.

"This study clearly shows that preventing exposure to tobacco smoke during pregnancy and postnatally may reduce the risk of hearing problems in children," senior author Dr. Koji Kawakami, of Kyoto University in Japan, said in a statement. "The findings remind us of the need to continue strengthening interventions to prevent smoking before and during pregnancy and exposure to secondhand smoke in children."

Related: Third-Hand Smoke: Scientists Warn Of Exposure To Cigarette Chemicals Where No One Has Smoked In Decades

Dr. Karen Wilson, the Debra and Leon Black Division Chief of General Pediatrics, and the Vice-Chair for Clinical and Translational Research for the Department of Pediatrics at the Icahn School of Medicine at Mount Sinai in New York, told Newsweek that she was not surprised by the results, although this is the first time she had seen such an association.

Secondhand smoke can increase the risk of ear infections in children, Wilson explained. Children who have had more ear infections are at a higher risk of hearing problems. Hearing is important for language development and learning, and if these impairments are not caught and reversed early on, they could interfere with a child's ability to learn, Wilson noted.