The hearing of smokers: a review

ABSTRACT

Amidst the factors that may cause hearing impairment, one can name smoking, since studies have shown that use of tobacco might have an ototoxic effect. The aim of this revision was to analyse scientific productions regarding smoking effects on the auditory system. Methodology was composed by database research, in which national and international scientific articles, in English or Portuguese, published from 2009 to 2016, were included. After being selected and examined, the articles were classified according to their type, and characterised into five categories: database, article title, author, year and country of publication. Afterwards, the criteria used by each author in their production were evaluated, considering population sample, age span and gender. Finally, analysis of auditory tests used in smokers and exclusion criteria of each study was performed. Thus, through the published studies, it was concluded that the use of tobacco influences the onset of hearing loss, damaging mostly high frequencies hearing thresholds and neural transmission of audio information.

Keywords:
Tobacco; Hearing; Smoking

RESUMO

Dentre os fatores que influenciam o aparecimento de alterações auditivas pode-se citar o tabagismo, já que estudos revelam que o uso do tabaco pode causar um efeito ototóxico na audição. O objetivo do presente estudo foi analisar as produções científicas sobre o efeito do cigarro no sistema auditivo. A metodologia constou de levantamento dos periódicos indexados nas bases de dados, e foram incluídos na revisão de literatura os artigos científicos nacionais e internacionais, publicados em língua portuguesa ou inglesa, entre os anos de 2009 a 2016. Posteriormente a seleção e análise dos artigos na íntegra, foram classificados de acordo com a sua natureza, caracterizando-os em cinco categorias: base de dados, título do artigo científico, autor, ano e país da publicação. Em seguida, foram analisados os critérios utilizados pelos autores dos respectivos artigos, levando em consideração a amostra populacional, a faixa etária e o sexo. Por fim, foram feitas as análises dos exames auditivos utilizados em fumantes e os critérios de exclusão de cada estudo. Assim, por meio dos estudos publicados conclui-se que o uso do tabaco influencia no aparecimento de perda auditiva, prejudicando principalmente os limiares auditivos das altas frequências e inclusive a transmissão neural da informação auditiva.

Descritores:
Tabaco; Audição; Hábito de Fumar

Introduction

The life expectancy of a smoker is 25 percent lower than a non-smoker. The most harmful substances present in tobacco and absorbed by the body are: thiocyanate (present in saliva), carboxyhemoglobin (found in blood), and carbon monoxide (in exhaled air). When inhaling cigarette smoke, approximately 2,500 harmful substances enter the body¹.

Hearing is one of the most important functions of the human communication system, especially in the oral language aspect, since the development of oral language is dependent upon the hearing system working perfectly. Otherwise, the individual may develop difficulties with communication, like delayed speech development, learning disabilities, and social and emotional disorders ².

There are several factors that cause hearing loss, such as noise exposure, meningitis, encephalitis, head trauma, otosclerosis, ototoxicity, diabetes, and others ³.

Authors⁴ show use of the cigarette can affect hearing due to the creation of oxygenation deficiency in blood vascular obstructions and changes in blood viscosity. However, there is still controversy about the effect of smoking on the auditory system because few studies exist concerning the subject.

Several studies have linked tobacco use with the presence of hearing loss, ^4-6 however, these studies suggest the need to expand research on this subject. More details are needed about the types of changes that tobacco can cause and locale of lesions.

Ototoxicity is caused by carbon monoxide (CO) present in components of the cigarette. This reduces oxygen levels in the cochlea, resulting in vasoconstriction, increased blood flow, reduced oxygen transport, and difficulty in oxyhemoglobin dissociation ⁷. All these changes can affect the blood supply to the cochlea, causing damage to the hair cells of the organ of Corti, and creating hearing problems ⁸.

The objective of this study was to analyze the scientific resources available in the literature published in the period from 2009 to 2016 in English, Portuguese, and Spanish, that concerned the effect of cigarette smoking in the auditory system.

Methods

This is a literature integrative article review with the purpose to gather and synthesize research results, in a systematic and orderly manner; to contribute to the deepening of knowledge of the subject investigated ⁹.

For the preparation of this integrative review, the following steps were conducted ¹⁰: definition of the investigated problem in the review and research objectives; selection of the sample establishing the inclusion and exclusion criteria of the publications; strategies for searching the literature; critical analysis of studies; data collection; presentation; and discussion of results.

The problem defined for the research was: What was produced in the literature about the hearing of smokers?

The pursuit of scientific publications was in national and international journals indexed in databases recognized internationally in the area of health sciences. Specifically, search was conducted using: Latin American and Caribbean Health Sciences Literature (LILACS), Science Electronic Online (SciELO), Medical Literature Analysis and Retrieval System Online (MEDLINE), and the Virtual Health Library (VHS). The following keywords were used: audição, fumantes / hearing; smoking" "emissões otoacústicas, fumantes / otoacoustics emissions; smoking", "perda auditiva, fumantes / hearing loss, smoking", "fumantes; PEATE / smoking, ABR" "fumantes; audiometria / smoking; audiometry" and "fumantes, processamento auditivo / smoking; Auditoryprocessing ".

Initially, access to publications was performed by reading and analyzing summaries through the Brazilian-based Regional Library of Medicine (BIREME) virtual library (www.bireme.br) to determine the literature that could meet the interests for this study.

In this process, criteria for inclusion were established. Such criteria were based on the following: national and international scientific articles published in the last seven years (2009 to 2016) in the languages of Portuguese, English, or Spanish. The studies needed to address tobacco as the subject and with a relation to the effects on the auditory peripheral and / or central auditory system.

During the search, a total of 484 articles, were found using the keywords and their combinations. No results were found when using the keywords"smokers; auditory processing.”

All articles where tobacco was presented with associated factors (noise, drugs, and chemical substances) were excluded, as were articles that reported the presence of middle ear alteration (18 studies), articles with unavailable texts (60 studies), in languages outside of the inclusion criteria (6 articles), and others concerning health problems due to cigarette use (304 studies). This resulted in a total of 474 discarded articles. The exclusion criteria took into consideration the articles, that after identification through titles and abstracts, did not fit the central objective of the research.

For analysis, only 10 articles were selected. Of the 10 selected articles, three were found exclusively in the LILACS database; five in MEDLINE; and two found both in the LILACS and MEDLINE databases. Regarding the language of the articles selected, five were in English and five were in Brazilian Portuguese.

After the selection and analysis of the full articles, the articles were then classified according to their type (national / international publication), and were characterized into five categories: database, title of scientific article, author, year, and country of publication.

Next, the criteria used by the authors of the respective articles were analyzed, with consideration of the following variables: population sample, age group, and gender.

Finally, for each individual study, the analysis of hearing tests for smokers and the exclusion criteria were performed.

Table 1 shows the studies classified according to their type (national / international) in the database, the scientific article title, author, year, and country of publication.

Table 1:
Articles on the relationship between the practice of smoking and the auditory system, classified according to their type (national / international publication): database, authors, year, and country of publication

• Legend: T = total articles

Table 2 presents the criteria used by the authors in the surveys, taking into account the following variables: population sample, age group, and gender.

Table 2:
Criteria used by the authors of the articles analyzed considering the variables: population sample, age group and gender

• Legend: T = total of articles; G = group; N = numbers

According to the present review, several tests were conducted to evaluate the auditory system of the sample subjects. Table 3 presents the analyzes of the auditory tests used to investigate the functioning of the peripheral and / or central auditory system in smokers: conventional audiometry (10; 100%), high frequency audiometry (4; 40%), logoaudiometry (2; 20%), suppressive effect of otoacoustic emissions (2; 20%), spontaneous otoacoustic emissions (1; 10%), transient evoked otoacoustic emissions (1; 10%), brainstem auditory evoked potentials (1; 10%). In addition, Table 3 also shows the exclusion criteria for each study. The studies that reported exclusion criteria eliminated all individuals who presented any symptoms or complaints of changes that could influence the audiological findings of the tests. This removed doubts about the effect of tobacco on the auditory system.

Table 3:
Auditory examinations and exclusion criteria used by the authors of the articles studied

• Caption: EOAT and EOATE = otoacoustic emissions evoked by transient stimulus; PEEP = brainstem auditory evoked potential; EOADP = otoacoustic emissions evoked by distortion product; EOAE = spontaneous otoacoustic emissions

Table 4 shows all the results of the exams in smokers presented by each study.

Table 4:
Results of hearing exams presented in studied articles

• Caption: EOAT and EOATE = otoacoustic emissions evoked by transient stimulus; EOADP = otoacoustic emissions evoked by distortion product; EOAE = spontaneous otoacoustic emissions

Literature Review

This article analyzes the scientific production concerning the effect of tobacco use in the peripheral auditory system and / or central nervous system; as various studies have hypothesized that cigarette smoking can cause hearing loss^{1,4-8,11)- (20}.

After reviewing national and international literature, there are few observable studies that investigate the auditory system of smokers, especially when using smoking as an individual factor. There are several relevant studies that relate smoking to other agents, such as noise and chemicals, but these were not included in this review because of the exclusion criteria already presented. We believe that it will be increasingly difficult to compose samples with exclusivity to smokers, due to the association that exists with several factors. For example, cigarette smokers are commonly exposed to ethyl. However, the general population is also exposed to harmful physical agents, such as noise and pesticides. Also, drug users, and individuals with psychiatric and emotional disorders, can experience damage to the central nervous system, as well as those with metabolic and hormonal disorders.

It is worth mentioning that half of the studies analyzed were performed in Brazil. The other studies were from only three other countries worldwide, including one in the United States, shown in Table 1. Considering this, audiology appears to be well-researched in Brazil, as it represents half of the analyzed articles that met the inclusion criteria. In addition, we believe that the tobacco industry might play a role in the lack of articles from countries outside Brazil, as research may affect the future decisions of current smokers. It is also worth considering that four of the surveys not performed in Brazil were done in a country with a lower income per capita (India), or in places with restricted access to information, such as Korea.

The literature review showed that all the publications found correspond to health and were published in magazines related to speech therapy ^5,12,18 otolaryngology ^4,13-15 diagnostics, ¹⁶ biomedicine, and medicine ^17,19. All articles had audiological diagnostics of smokers as a principal theme. Only one article featured research that included different factors within the same study, but the results did not interfere with the information concerning smokers⁵.

The audiometry tonal threshold is considered the gold standard for obtaining thresholds and audiometric configuration in adults. Therefore, this has been used in all the articles found; some used this for comparison of hearing thresholds of smokers and nonsmokers ^4,5,13-17,19, and others only for application of the exclusion criteria, since individuals could not have thresholds above 25dBHL ^12,18. Only three studies used exclusively conventional tonal audiometry for hearing research^5,15,19, and the others added other forms of evaluation. It was observed that the latest studies are those that used additional laboratory tests as a method of evaluation (as well as audiometry), probably due to the availability of high-value equipment. In other examples, without these additional methods of evaluation, the research protocol may not have been complete. In Europe and North America, complementary and otoneurogical exams are routine.

Regarding the results of the tests, conventional audiometry was found, and in the majority of articles, tonal thresholds were within normal standards ^{4,12-14,16,18}. Among these studies, some auditory thresholds in smokers were worse when compared to the thresholds of non-smokers, with a statistically significant difference ^4,13,16. There was only one study that presented no significant differences regarding the auditory thresholds between groups ¹⁴. The others did not compare hearing thresholds between groups ^12,18. Four study groups, among those selected, found altered auditory thresholds ^5,15,17,19 and one of them found hearing loss only in the frequency of 8000 Hz ¹⁷. When compiling and analyzing all the results, it was observable that researchers found hearing threshold damage among smokers when compared to nonsmokers, even though there was no statistically significant difference, demonstrating that smoking is harmful to the auditory organ.

Among the studies that contained hearing thresholds within normal limits, the maximum age for featured subjects in the sample was 59 years old ¹² and studies that had altered the hearing thresholds of the sample population included subjects up to 60 years old ^15,17 and two with a maximum of up to 90 years old ^5,19. One such study only evaluated the hearing of the elderly, and featured individuals with more than 60 years of age with exposure to cigarette smoke and other factors⁵, and the results showed no normal hearing thresholds in all subjects over the age of 70. However, the worse in that specific study was the group of smokers. One may assume that people over the age of 60, who were studied between the years of 2009 and 2016, grew up in an era where the act of smoking represented status. Advertising of the cigarette industry was much more pronounced when compared to recent years, and such advertising came without the indications of possible complications. Today, in Brazil and many other countries, it is mandatory to include in cigarette advertising some undesirable imagery concerning smoking and information about the negative effects, even on the pack of cigarettes bought at a store. It is also possible to observe the concern of the elderly today to maintain a healthy life, avoiding habits harmful to health such as smoking.

In high - frequency audiometry, results were similar to those of conventional audiometry, with thresholds within the normal range and worsening of thresholds in smokers, with a statistically significant difference between the groups of smokers and non-smokers in all studies that performed this test ^4,13,16,17.

Another question related to the hearing of smokers is whether the number of cigarettes consumed would influence the results of hearing tests. Four articles studied this hypothesis ^14-17. In relation to the hearing thresholds, authors of two studies reported that there is worsening of thresholds as the number of cigarettes smoked increased^15,16. However, other authors disagree with this theory^14,17, and one of such articles showed a worsening threshold in relation to the number of cigarettes consumed in only ¹⁷ the frequency of 12 kHz. It is known that, according to the time of exposure to the toxic agent, there is an increase in damages to health in general. Thus, it is expected that with the greater the number of cigarettes consumed and greater time of usage, the effects will only worsen. This likely applies to not only in the auditory system, but also throughout the body.

Among the selected articles, only one described tinnitus as an auditory symptom in the smoking group ⁴.

As seen in Table 3, some studies used otoacoustic emissions as a method ^4,14,16 where the examination purpose is to evaluate the cochlear amplification mechanism (OHC). Regarding the otoacoustic emissions evoked by transient stimulus (ETEOE), two studies found decreased amplitudes in the group of smokers compared to nonsmokers^4,14. And in another study, ¹⁶ no differences were found between groups. The difference in amplitude response between groups also occurred in the otoacoustic emissions, distortion product (DPOAE) ^14,16. Among the items studied, only one evaluated the olivocochlear system through the suppression effect. This presented, as a result, a greater suppression value in the smoking group^4).Increased suppression in smokers is caused by the interference of nicotine in the neural transmission of auditory information, thus affecting the higher neural centers that may result effect in an inhibitory efferent in outer hair cells. This creates an acceleration effect on acetylcholine, which is the efferent neurotransmitter in the auditory system ²⁰.

All the articles selected presented, as an exclusion criterion, the presence of alteration of the middle ear and/or previous otological diseases. In a few discarded hypotheses, studies performed immittanciometry ^{4,12,14,16,18}. Among these, only one study ¹⁸ aimed to compare the imitanciometry findings between groups of smokers and nonsmokers, and due to this, the sampled individuals should present hearing thresholds within the normal standards. The result of this study showed that the peak pressure tympanometry was the only parameter that could differentiate between smokers and nonsmokers. With smokers, the pressure was increasingly shifted to negative ¹⁸.

There are not many recent studies on the Auditory Brainstem Evoked Potential (BAEP) in the smoking population. When searching, only one study used the research of auditory brainstem response in the smoking population ¹². The authors of this study hypothesized that tobacco use can cause high brain stem involvement, as there was an increase in latencies of I and V waves and of III-V inter-latencies in both ears of smokers. Therefore, it is concluded that tobacco may interfere with the neural transmission of auditory information, influencing the latencies and inter-latencies of the BAEP examination waves especially considering that this test has the capacity to evaluate the neurophysiological integrity of the auditory pathways of the brainstem.

With this knowledge, it is important to emphasize the importance of monitoring the hearing of smokers and the performance of diversified exams, mainly through the Evoked Otoacoustic Emissions Tests and the BAEP, as objective examinations that evaluate the functional integrity of the auditory system. Thus, they are able to identify possible alterations caused by cigarette smoking, and be used to provide caution and prevent the early auditory alteration caused by this harmful agent.

Presently, it can be observed that procedures, such as otoacoustic emissions, suppression effect, medium and long latency auditory, evoked performance potentials, favor the enrichment of the literature and diagnosis. We believe, however, that the composition of smoking groups with no association to other harmful agents in the current world population will remain difficult, due to the very characteristics of modern society. It is impossible, at present, to consider the existence of any study where otherwise healthy subjects start smoking for a period of time, exclusively for research. There are clear ethical standards for human studies, in-addition to moral conflicts that would likely arise with the researcher. One solution may be to carry out experimental studies.

Conclusion

All studies evaluated in the present review show data that imply that there is an increased risk of hearing loss in smokers. Several types of hearing evaluations were used in these individuals, allowing to make it possible to conclude that tobacco use influences the appearance of hearing loss, since auditory thresholds are worse with smokers. It is important to highlight that through the analysis of the articles, it is evident that the use of tobacco mainly affects the hair cells of the base of the cochlea, since the high frequencies are the most harmed. This result was also shown by the low level of response of evoked otoacoustic emissions, mainly by distortion product, which evaluates a frequency range higher than that of transient otoacoustic emissions.

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Publication Dates

• Publication in this collection
  June 2017

History

• Received
  28 July 2016
• Accepted
  20 Apr 2017