Association of cigarette smoking with hearing loss: Cross sectional study among sample population of Kolar

 

Ashwini K Shetty^1*, Karthiyanee Kutty², Vinutha Shankar M S³

 

 

Abstract               Background: The link between cigarette smoking as a risk factor for hearing loss was established over 40 years ago. This study was an attempt to observe the association between smoking and changes in hearing thresholds in a sample population of Kolar. Aims and Objectives: To record the auditory thresholds for various frequencies of smokers and age matched non-smokers and to study association of pack years of smoking with changes in auditory thresholds for both AC and BC at different frequencies Methodology: The study included 50 male cigarette smokers of age group between 20-40 years and 50 age matched male non smokers, who were selected based on inclusion and exclusion criteria. An assessment of auditory thresholds was done for different frequencies by using pure tone audiometer (ELKON-GIGA3) for both study and control groups in a sound proof room. The data collected was entered in master chart and statistically analyzed. Conclusion: The present study revealed that, smoking causes increase in both air conduction and bone conduction thresholds at all frequencies and if a subject has smoked regularly for a period of 2 or more years it induces changes in both auditory air and bone conduction thresholds.

Key Words: Smoking, hearing loss, auditory thresholds.

 

INTRODUCTION

Smoking is the leading cause of preventable death in the world. The effects of smoking represent a global pandemic of enormous proportions.¹ By recent counts, there are about 94 million smokers in India, Almost 5%of women and a third of all men aged between 30 and 69 smoke and smoking of cigarettes causes death 10 years sooner.² The dangerous component of a cigarette is “smoke”. Smoke contains harmful gases like carbon monoxide and nitrogen oxide. Over a century ago, the association between excessive smoking and deafness was noted by de La Charrière in 1875.³ Information on the effects of smoking at the cochlear and auditory pathway has become available only recently. A few population based studies have shown relation between smoking and hearing loss.^4,5 Various studies have shown cigarette smoking has got deleterious effects on peripheral and central auditory nervous system^{6,7,8,9,10,11} The present study aims at observing the association between smoking and changes in hearing thresholds in a sample population of Kolar.

 

MATERIALS AND METHODS

The study group consisted of 50 cigarette smokers and 50 age matched non smokers.The subjects were recruited based on various inclusion and exclusion criteria from teaching and non teaching staff of Sri Devraj Urs Academy of Higher Education and Research and also attenders of patients coming to R.L. Jalappa Hospital, Kolar after taking informed consent. Ethical clearance was also obtained from Institutional Ethical Clearance Committee for the study.

Inclusion Criteria:

Study Group: Male smokers of age group between 20-40years who are not exposed to occupational noise.

Control Group: Non smoking males of age group between 20-40 years without occupational noise exposure.

Exclusion Criteria:

Study group: Subjects with history of use of ototoxic drugs like streptomycin, cisplatin, neomycin, gentamycin,with history of head injury and history of ENT infections in past 3 months, with chronic medical illness like diabetes, hypertension etc.

Control Group: Same as above subjects being non smokers.

Methodology: Based on above predetermined inclusion and exclusion criteria, subjects were divided into study (smokers, n=50) and control (non smokers, n=50) groups. Study subjects thus selected were given a questionnaire to collect information regarding their smoking history expressed in pack years. A detailed general physical and clinical examination ear, nose and throat was carried out to rule out any unidentified pathology. An assessment of auditory thresholds was done for different frequencies by using pure tone audiometer (ELKON-GIGA3) for both study and control groups in a sound proof room. The parameters studied in pure tone audiogram are air conduction (AC) and bone conduction (BC) hearing thresholds of both the ears at various frequencies of sound. They are recorded on audiogram chart which depicts the auditory thresholds of the particular ear The data collected was entered in master chart and statistically analyzed using appropriate statistical test like student t test, ANOVA, Post Hoc test.Significance was assessed at 5% level of significance.

 RESULTS

The study subjects were age matched with p=0.376. Study showed that there significant difference in AC and BC thresholds between smoker and non smoker groups at all frequencies in right and left ear (Table 1and2). For further analysis of data the smokers group were divided based on number of pack years(PY) as <2 PY, 2-5 PY, >5 PY and for nonsmokers, the number of pack years was set to zero(0 PY).¹² Comparison of AC and BC thresholds were done between 0 pack years <2 pack years, 2-5 pack years and >5 pack years groups by using ANOVA and it depicts that there is significant difference in AC and BC thresholds between the groups at all frequencies in the right ear and left ear(Table 3and 4). A Post-hoc Tukey test was carried out for table 3 and 4 to determine which groups differ from each other depicted that there is no significant difference between AC and BC thresholds 0 pack years and < 2 pack years of smoking at all frequencies in right and left ear but significant differences of AC and BC thresholds were found between 0 pack years and smokers with 2-5 pack years, >5 pack years at all frequencies (Table 5and6).

Table 1: Comparison of AC thresholds in decibels between smokers and nonsmokers in right and left ear

Table 2: Comparison of BC thresholds in decibels between smokers and nonsmokers in right and left ear

 

Table 3: Comparison of AC and BC thresholds of right ear between groups with different pack years

 

Table 4: Comparison of AC and BC thresholds of left ear between groups with different pack years

Study group	AC
	0.25 kHz	0.5 kHz	1 kHz	2 kHz	4 kHz	6 kHz	8 kHz
0PY	13.5±4.82	13.9±4.76	12.1`±4.05	11.4±5.05	12.7±5.62	12.5±5.36	12.8±5.90
<2 PY	16.67±4.82	16.67±6.37	16.04±6.75	15.21±6.51	18.33±9.52	17.92±8.71	15.21±8.01
2-5 PY	22.31±4.84	23.46±4.27	20.38±5.19	23.08±6.93	26.15±9.82	26.54±9.87	19.23±8.62
>5 PY	22.31±7.53	23.08±6.30	26.15±13.56	25.77±12.39	29.23±12.05	35.00±11.18	26.15±12.61
p value	<0.001**	<0.001**	<0.001**	<0.001**	<0.001**	<0.001**	0.001**
	BC
	0.25 kHz	0.5 kHz	1 kHz	2 kHz	4 kHz	6 kHz	8 kHz
0PY	5.9±3.30	6.5±3.07	6.0±3.19	5.1±3.70	5.6±3.86	-	-
<2 PY	9.79±5.00	9.79±4.77	8.96±6.59	8.13±5.86	10.21±8.91	-	-
2-5 PY	11.92±6.30	10.38±5.94	10.77±5.34	11.92±7.23	14.62±6.60	-	-
>5 PY	11.15±6.18	12.69±6.65	17.69±6.96	17.31±11.48	19.23±8.13	-	-
p value	<0.001**	<0.001**	<0.001**	<0.001**	<0.001**	-	-

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 5: Comparison of auditory threshold in AC and BC for Right ear in study subjects-Post hoc analysis

 

 

Table 6: Comparison of auditory threshold in AC and BC for left ear in study subjects-Post –hoc analysis

DISCUSSION

Cigarette smoking is an important risk factor for chronic lung diseases and cardiovascular diseases. Relatively little data exists on the exposure of cigarette smoking as a risk factor for hearing loss, although link was established over 40 years ago. This study was an attempt to observe the association between duration of smoking and changes in hearing thresholds in a sample population of Kolar. Pure tone audiometry was used to record auditory thresholds in our study, which is a simple, inexpensive, qualitative and quantitative procedure. Study included age matched samples between 20-40 years, as hearing loss is an inevitable consequence of aging. With increasing age there is physiological alteration in hearing acuity called “presbyacusis” Present study showed that the smoker group had higher threshold of hearing at all frequencies as compared to age matched non smokers indicating smoking affects both air and bone conduction auditory thresholds. Similar results were shown in a study which compared the auditory thresholds, within a group of male smokers and non-smokers aged between 18 and 40 years.¹³Studies have also shown that the percentage of hearing loss was greater for smokers at all measured frequencies.¹⁴ The possible explanation for conductive hearing loss among smokers may be a higher prevalence of rhino sinusitis or eustachian tube dysfunction.^15,16,17,18 Sensorineural hearing loss might be due to an oxidative damage caused by toxic substances inhaled with the cigarette smoke.¹⁹ Three putative mechanism have explained the relationship between smoking and hearing loss The first mechanism may be related to hypoxia; both nicotine and carbon monoxide in cigarette smoke have been shown to reduce the oxygen supply to fetal tissueand also elderly individuvals.^20,21,22,6 The second putative mechanism may pertain to the interaction between nicotine and nicotinic acetylcholine receptors (nAChRs) which are critical components of the auditory pathway, from the cochlea to the temporal lobe, and the descending auditory pathway.^7,8,9,23The neurophysiological mechanism that may potentially explain the association between adolescent smoking and neurocognitive deficits is that the auditory thalamocortical and cortigofugal pathways, continue to grow into late adolescence ^8,9,10and these pathways are particularly susceptible to damage, if environmental toxins like nicotine are introduced during their developmental emergence.^7,11 On further analysis of our study showed that there was no significant difference between hearing thresholds at 0 PY and < 2 PY of smoking at all frequencies in both right and left ear but significant differences of hearing thresholds were found between 0PY and 2-5 PY, 0PYand>5PY,<2PYand2-5PY,<2PYand>5PY indicating that if a subject has smoked regularly for a period of 2 or more years it induces changes in both auditory air and bone conduction thresholds. Although earlier studies have shown changes to set in at as early as one year.¹² Because of the smaller sample size and unequal distribution of samples between the groups these results need to be confirmed by population based studies. Present study included only male subjects; consequently generalization cannot be made across genders. Pure tone audiometry is a subjective test and hence results need to be confirmed by objective tests like BERA, OAE’s.

 

CONCLUSIONS

The present study revealed that smoking causes increase in both air conduction and bone conduction thresholds at all frequencies and if a subject has smoked regularly for a period of 2 or more years it induces changes in both auditory air and bone conduction thresholds.

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