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 While previous research suggests that adult smokers are at greater
risk of hearing loss than nonsmokers, less is known about how much
smoke exposure during infancy or pregnancy might impact hearing.
For the current study, researchers examined data on 50,734 children
born between 2004 and 2010 in Kobe City, Japan. Overall, about 4
percent of these kids were exposed to smoking during pregnancy or
infancy, and roughly 1 percent had tobacco exposure during both
periods.
Hearing tests done when kids were 3 years old found that 4.6 percent
of the children had hearing loss.
They were 68 percent more likely to have hearing loss if they were
exposed to tobacco during pregnancy, and 30 percent more likely if
they inhaled second-hand smoke during infancy, the study found.
When kids had smoke exposure during both periods, they were 2.4
times more likely than unexposed kids to have hearing loss.
"Patients with the greatest risk of hearing impairment are those who
are directly exposed to maternal smoking in the womb," said Dr.
Matteo Pezzoli, a hearing specialist at San Lazzaro Hospital in
Alba, Italy.
"Interestingly, the exposure to tobacco in early life seems to
further strengthen the prenatal toxic effect," Pezzoli, who wasn't
involved in the study, said by email.
When pregnant women smoke, it may harm fetal brain development and
lead to auditory cognitive dysfunction, Pezzoli added. Tobacco smoke
may also damage sensory receptors in the ear that relay messages to
the brain based on sound vibration.
Globally, about 68 million people have a hearing impairment that is
thought to have originated in childhood, Koji Kawakami of Kyoto
University in Japan and colleagues note in Paediatric and Perinatal
Epidemiology. Kawakami didn't respond to requests for comment.
Researchers assessed children's hearing using what's known as a
whisper test. For these tests, mothers stood behind their kids to
prevent lip reading, then whispered a word while kids' had one ear
covered.
While this test is simple and considered an accurate way to assess
hearing in adults and older children, there's some concern about how
reliable the results may be in young kids.
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It's considered more reliable when it's done by trained clinicians
and specialists and less reliable when it's done by primary care
providers, researchers note. It's unclear how accurate study results
based on tests administered by the children's parents would be,
researchers acknowledge.
The study also wasn't a controlled experiment designed to prove
whether or how tobacco exposure during pregnancy or infancy might
directly cause hearing loss in kids.
"There was no standardized medical evaluation of hearing or
examination of the ears by ear specialists," said Dr. Michael
Weitzman, a pediatrician and hearing researcher at New York
University who wasn't involved in the study.
"Moreover, the severity of hearing loss could not be ascertained in
this study, and it did not follow up the children throughout their
childhood so we do not know if what they found attenuated or got
worse over time," Weitzman said by email.
Still, the results add to the evidence linking tobacco exposure to
hearing problems in kids, Weitzman said.
To protect children against hearing problems caused by cigarette
smoke, it's important for women to quit before they become pregnant
or as soon as they discover they're pregnant, said Huanhuan Hu, a
researcher at the National Center for Global Health and Medicine in
Japan who wasn't involved in the study.
"To minimize the chance that their baby will be exposed to tobacco
smoke in the womb, other family members should also quit, or at
least not smoke at home or nearby the pregnant women," Hu said by
email.
SOURCE: https://bit.ly/2IAPU2W Paediatric and Perinatal
Epidemiology, online June 5, 2018.
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