Exposure to tobacco smoke while in the womb can lead to diminished hearing by adolescence, doctors have found in the first study ever to link tobacco use and hearing impairment.
The new research suggests that compounds contained in tobacco smoke cross the placenta and exert harmful effects on the auditory system.
The analysis, conducted by Drs. Michael Weitzman and Anil Lalwani of NYU Langone School of Medicine in Manhattan, focused on both maternal smoking and tobacco use by other household members.
"This is the first time [science] has produced evidence that the ability to hear can be affected by smoke," Weitzman said Thursday.
"I think some people would say this adds to the litany of horrible consequences of an epidemic involving a man-made product that began causing serious health effects 110 years ago with the massive sale of tobacco products," he said.
In the past, doctors have linked low birth weight, asthma, sudden infant death syndrome and recurrent ear infections to both maternal smoking and exposure of the mother to secondhand smoke while pregnant.
Weitzman noted that even though his research was not designed to pinpoint a mechanism by which tobacco smoke damages the ability to hear, it is possible, he said, that tobacco's byproducts can injure the developing ear in numerous ways.
The research focused on hearing loss due to nerve damage.
"It is possible that [hearing loss] might occur because of decreased blood flow and decreased oxygenation, or higher carbon monoxide levels," he said.
Weitzman, a professor of pediatrics and environmental medicine, studied the medical records of 964 adolescents between the ages of 12 and 15 who had participated in the federal government's National Health and Nutrition Examination Survey during 2005-06.
Parents were asked about prenatal smoke exposure. Weitzman said the parents -- especially mothers -- usually lie about cigarette usage during pregnancy because of the stigma attached to the habit and its injurious effects on the fetus. Sixteen percent of parents admitted to smoking.
Reporting in the journal Otolaryngology -- Head and Neck Surgery, the team found that smokers' children were more likely to suffer a loss of hearing audible sounds, such as those that occur during normal speech.
There was also a threefold increase in the odds of low-frequency hearing loss in one ear, according to the research.
Lalwani studied the losses in tone. The aim of their research, Weitzman said, was to determine two factors: exposure to prenatal tobacco smoke and what doctors call sensorineural hearing loss, or impairment associated with nerve damage.
This kind of hearing loss is subtle but debilitating, Weitzman and his colleagues say.
"If you have subtle hearing loss, it can change how you perceive the world, you may miss every other word that people are saying," Weitzman explained.
"With severe hearing loss, people easily recognize that. Someone makes sure you get a hearing aid or a cochlear implant; people seat you in the front of the room -- you get a lot of help.
"But when it's subtle," he continued, "the assistance you need really isn't there."
He said kids with subtle hearing loss perform poorly in school and tend to have behavioral problems because of their inability to adequately hear.