The findings of a recently-published study by researchers in Seoul, South Korea, support previous evidence that smoking is an independent cause for hearing loss, even in young adults. Both the size and design of the study brace its conclusions.
Published in the April issue of the journal, Scientific Reports, the paper, Self-reported and cotinine-verified smoking and increased risk of incident hearing loss describes a large cohort study performed in 293,991 Korean adults free of hearing loss who underwent a comprehensive screening examination and were followed for up to 8.8 years.
The study used self-reporting smoking status as one check, but also, significantly, measured urine for levels of cotinine, a major metabolite of nicotine and a reliable and objective biomarker that reflects smoking status. The latter can reduce misclassification bias in self-reporting methods, dependence on which in many earlier studies weakens their evidence, claim the researchers.
Smoking status thus verified were independently associated in the study with an increased incidence of bilateral hearing loss. The researchers’ findings indicate smoking is an independent risk factor for hearing loss.
The authors point to previous studies that suggest smoking can cause negative alterations in the cochlea, leading to different effects on the base and apex of the cochlea via microvascular compromise and induced hypoxemia. No previous study, however, has shown the effects of both subjective and objective smoking measures on the development of hearing loss.
The significance of the associations confirmed held up even after adjusting for various confounders, including occupational noise exposure, although the associations were not found to statistically differ by sex, and the number of women smokers in the cohort was low.
The study has several limitations, which included: the association between smoking and hearing could be investigated with only low-frequency data; leisure exposure, the main cause of noise-induced hearing loss, was not measured at a comprehensive examination; information on ototoxic drugs (i.e. cisplatin and aminoglycoside antibiotics) was not available; detailed analyses on second hand smoking were not possible in the study, even though second hand smoking has been reported to be associated with hearing loss and can affect urine cotinine levels.