In our study, about 8.4% of the noise-exposed group showed BVFL findings on laryngoscopy. Among them, laryngitis accounted for the largest proportion, with a prevalence of about 5.3%. It was confirmed that BVFLs were about 1.5 times more likely to occur in the noise-exposed group than in the unexposed group after adjustment for confounding variables. Our results suggest that noise exposure in the workplace could be a risk factor for BFVLs. More than 100 years ago, French otolaryngologist Etienne Lombard reported the Lombard effect, by which speech amplitude involuntarily increases when background noise increases. [11] Also, apart from that effect, if noise in the surrounding environment interferes with communication, excessive voice effort might intentionally be made to compensate for it. [12] Our study is the first population-based study to confirm through laryngoscopy that BVFLs could be caused by working in a noisy environment.
The vocal fold is anatomically divided into 5 layers. The surface of the vocal fold has a stratified squamous epithelium that can withstand the stress of vocal fold vibration. Deep below it is the lamina propria, which is further divided into three layers. [13] The superficial layer of the lamina propria is Reinke's space, which is filled with extracellular matrix composed of collagen, elastin, and hyaluronic acid and plays an important role in voice production through vocal fold vibration. [14, 15] The regular vibrations of Reinke's space periodically close the vocal folds and produce the voice. [16] Vibrations that are too strong or for that continue for a long period of time cause vascular congestion and swelling in the middle of the vibrating part of the vocal fold. [3] If such voice abuse continues chronically, lesions such as laryngitis, nodules, polyps, cysts, and granulomas occur in the submucosal edema. Also, it is assumed that glottic sulcus forms after any cyst is naturally emptied, which causes the vocal fold to become less flexible and the physical volume to decrease, and that process increases the effort required to operate the vocal fold. [16]
Analyzing and managing risk factors for BVFLs is essential for treating and preventing them. Vibratory trauma is the most common risk factor for voice disorders, and the frequency of occurrence in the occupational group requiring a lot of voice use was reported to be high. In Poland, it was reported that occupational voice disorders account for about 20% of all occupational diseases. [17] In addition, lifestyle habits such as smoking, alcohol consumption, and caffeine intake and chronic medical conditions such as gastroesophageal reflux disease and obesity have also been reported to be associated with BVFLs or voice disorders. [18–22] In population-based data provided by the National Health Insurance Service of South Korea, the middle-aged group showed the highest prevalence of BVFLs, which is similar to our results in this study. However, in the 2014 data of that study, the peak age of prevalence shifted from the 50s to the 60s compared with previous data. [1] That was judged to reflect an increase in healthy life expectancy. Although middle-aged people are still active in social activities, their neuroendocrine function might be deteriorating, and various diseases could develop as a result of abnormal cortisol secretion in response to stress. [23] The high incidence of BVFLs in middle-aged people is thought to be related to that process, but it has not been clearly established.
The study of Rontal et al., in which 283 workers in a noisy environment were subjected to laryngoscopy, reported that 21 patients (8%) showed laryngitis, vocal nodule, or vocal polyp findings. [24] Most of the participants in that study were smokers, and although voice abuse in the workplace was considered to be the main cause, excessive dust and fumes in the workplace were considered to be a secondary cause. They recommended that aspects related to mental health, such as stress caused by noise, should also be considered in future studies. We found no significant differences in the mental health items (moderate to severe stress perception, depression for more than 2 weeks within the past year, and suicidal ideation within the past year) reported by the two groups (with and without occupational noise exposure), so we did not consider them. Rontal et al. found that workers in noisy environments showed a 30% recurrence rate after laryngeal surgery and argued that a high possibility of treatment failure due to continuous voice abuse could be a risk if the work environment is not considered. That result supports the importance of reducing noise levels in workplace environments.
Several previous studies have reported hearing loss, cardiovascular disease, premature birth, and other medical conditions as diseases that can be caused by occupational noise exposure. [25] Based on that clinical evidence, institutional arrangements and environmental standards for working environments have been made. However, awareness of vocal fold diseases caused by noise exposure is still lacking, even though it was first pointed out in the 1970s. [24] Voice problems tend to be overlooked clinically because they do not affect livelihoods or cause fatal discomfort. Many patients with voice problems are unaware of treatment options or expect their symptoms to improve on their own, with only a small number of patients receiving professional treatment for their voice problems. [26] If vocal fold disease is left unattended, a vicious cycle of increasing vocal effort can occur. That cycle can be prevented by managing vocal hygiene, so it is important to know that BVFLs can be an occupational disease not only in occupations that require a lot of voice use but also among general workers in noisy environments. We found prevalence and OR associations between occupational noise exposure and BVFLs. Although prevalence and ORs do not indicate a causal relationship, it is necessary to pay attention to these results because the relationship between occupational noise exposure and BVFLs has been overlooked clinically. In the 5th KNHANES data that we used, 19,937 people with and without laryngoscopy data indicated whether they were exposed to noise, and 10.6% of them responded that they had been exposed to work noise for more than 3 months. Because the frequency of occupational noise exposure in the general population is high, it is important to recognize the risk of vocal fold diseases among workers exposed to noisy environments. Precautions when talking in a work environment, voice hygiene education, quick self-awareness of voice problems, and regular screening should be recommended. [27] If vocal cord–related symptoms appear, medical staff should advise the worker to undergo laryngoscopy during a rapid specialist examination.
Our study has several limitations. First, as a cross-sectional study, it cannot clearly explain the causal relationship between occupational noise exposure and BVFLs. Second, a major limitation is that we did not have access to information about noise intensity or accumulated exposure time. Third, it is an exposure history survey that relied on self-reports by the participants. Given our results, we suggest that a large-scale prospective study is needed to determine the prevalence of BVFL in objectively evaluated noise exposure environments and workers.