Exposure to tobacco smoke is linked to hearing impairment in children, according to a new Kyoto University study published in the peer-reviewed journal, Paediatric and Perinatal Epidemiology.

The study, titled, “Exposure to tobacco smoke prenatally and during infancy and risk of hearing impairment among children in Japan,” was authored by Calistus Wilunda, Shiro Tanaka, Satomi Yoshida. Takeshi Kimura, Yuji Kanazawa, and Koji Kawakami.

The study included 50,734 children born between 2004 and 2010 in Kobe City, Japan. Smoking before, during, and after pregnancy was measured using parent-reported questionnaires.

Hearing was assessed using the Whispered Voice test, according to the BMJ, which is commonly used for screening for hearing impairment in adults and children. During the Whispered Voice test, the examiner would stand behind the seated patient (to prevent lip reading), whisper a combination of letters and numbers, and ask the study participant to repeat the sequence.

If a child responded correctly, the examiner would consider their hearing normal. If a child responded incorrectly, the examiner would repeat the test, using a different letter-number combination. The child would pass the test by repeating at least three out of a possible six letters or numbers correctly. Each ear was tested individually.

Of the included children, 3.9 percent were exposed to second-hand smoke at four months of age. At four months of age, and during pregnancy, 0.9 percent were exposed to tobacco smoke. Of the included children, 15.2 percent were only exposed to maternal past smoking, and 3.8 percent of children were exposed to smoking only during pregnancy.

The prevalence of hearing impairment at age 3 was 4.6 percent, results show. Children exposed to only maternal past smoking during pregnancy had a 26 percent increased relative risk of hearing impairment. Children exposed to only second hand smoke had a 30 percent increased relative risk. Children exposed to smoking only during pregnancy had a 68 percent increased relative risk.

In a press release supplied to Wiley Online Library, Kyoto University researchers concluded the following.

“This study clearly shows that preventing exposure to tobacco smoke during pregnancy and postnatally may reduce the risk of hearing problems in children. The findings remind us of the need to continue strengthening interventions to prevent smoking before and during pregnancy and exposure to second-hand smoke in children.”

The results, researchers wrote, indicate that exposure to tobacco smoke, prenatally and postnatally, is linked to hearing impairment. In other words, preventing exposure to tobacco smoke before, during, and after pregnancy may reduce the risk of hearing problems in children.

Kyoto University’s study is the first to explore and establish the link between parental smoking, exposure to tobacco smoke, and hearing impairment. The risks of child exposure to tobacco smoke are well-known. For instance, a longitudinal, multi-generational study published in the Official Journal of the American Academy of Pediatrics in 2013 has shown that children of current and former smokers, apart from facing health risks as children, also face an elevated risk of smoking.