The researchers drew on data from the 2005-2006 National Health and Nutrition Examination Survey (NHANES), a cross-sectional survey of Americans conducted under the auspices of the CDC. Designed to assess the health and nutritional status of children and adults, NHANES is unique in that it combines in-home interviews and physical examinations. The examinations include collection of blood and urine samples and standard audiometry testing for 12- to 19-year-olds.
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October 2013Additionally, self-recognition of hearing impairment is assessed by asking people to describe their hearing (sans hearing aid) as excellent, good, having a little trouble, moderate trouble, a lot of trouble or deaf.
The NHANES blood analysis included the measurement of cotinine, a nicotine metabolite that was used as a biomarker for active smoking and exposure to SHS. Adolescents with serum cotinine levels of .05 µg/L to 15 µg/L were defined as exposed to SHS if they denied smoking themselves over the previous five days; those whose serum cotinine exceeded 15 µg/L or reported smoking within the previous five days were considered active smokers, and participants who reported no smoking within the previous five days and had no detectable serum cotinine levels were considered nonsmokers and unexposed to SHS.
Of the 1,533 participants, those considered SHS-exposed had higher rates of bilateral and unilateral SNHL at all frequencies tested, with the differences reaching statistical significance for unilateral low-frequency hearing loss. Overall, SHS exposure was associated with nearly a two-fold increase in the risk of hearing loss in this population. Even worse, lead author Anil K. Lalwani, MD, of the departments of otolaryngology, physiology and neuroscience and pediatrics at New York University Langone Medical Center, and colleagues suggested that the hearing loss might be at an early stage and might progress over time. They also observed higher rates of hearing loss in participants with higher serum cotinine levels, suggesting a possible dose-response effect.
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These findings prompted the authors to wonder if the negative effects of SHS might begin even before birth: Would a mother’s smoking during pregnancy affect her child’s hearing later on? Once again, they turned to data from NHANES 2005–2006. This time, they included only children between 12 and 15 years of age, because information on maternal smoking behavior was available only for children aged 15 years or younger, while audiometric data were available only for children aged 12 years or more. After exclusion for factors such as incomplete information on maternal smoking or hearing test results, the study sample included 964 adolescents. Of those, 155 (16.1 percent) were born to mothers who had smoked at some time during pregnancy, including 96 (61.9 percent) during the first trimester only. Because of the small sample size, the authors did not determine whether a dose-response relationship existed between maternal smoking and the child’s subsequent hearing loss (JAMA Otolaryngol Head Neck Surg. 2013;139:669-677).