|Year : 2013 | Volume
| Issue : 1 | Page : 1-4
A study of effect of shift work, sex, and smoking on development of ONIHL in plastic weavers
Jayesh D Solanki, Hemant B Mehta, Chinmay J Shah, Pradyna A Gokhale
Department of Physiology, Government Medical College, Bhavnagar, Gujarat, India
|Date of Web Publication||6-Mar-2013|
Jayesh D Solanki
Department of Physiology, 4th Floor, Behind S. T. Bus Stand, Jail Road, Bhavnagar, Gujarat
Source of Support: None, Conflict of Interest: None
Background: Exposure to Occupational noise is the major avoidable cause of permanent hearing loss that is preventable by protective measures. Present study evaluated hearing profile and effects of shift, sex, and smoking on hearing loss in plastic weavers working in textile industry exposed to impact type of noise. Materials and Methods: A cross-sectional study of hearing threshold of various shift workers of plastic weaving industries (18 males, 32 females) at various frequencies was done and effect of various factors was tested at low and high frequencies and compared at 4 kHz, 6 kHz, and 8 kHz statistically. Results: Hearing thresholds were significantly higher at high frequencies than speech frequencies, in day shift workers than night shift workers and within day shift workers more with continuous type of shift work than interrupted type. Females showed better hearing than males and for non-smokers than smokers, but the difference observed in both instances proved statistically insignificant. Conclusion: It can be concluded that the use of alternate day and night shift, interrupted day shift may be used to prevent hearing loss and for further confirmation few more studies are warranted. Being female and non smoking also proved an advantage. Comparatively, mild to moderate degree of hearing loss further reinforces the scope of prevention by hearing protective devices and interrupted shift design of work.
Keywords: Hearing loss, Hearing thresholds, Occupational noise, Shift workers, Smoking
|How to cite this article:|
Solanki JD, Mehta HB, Shah CJ, Gokhale PA. A study of effect of shift work, sex, and smoking on development of ONIHL in plastic weavers. Indian J Otol 2013;19:1-4
|How to cite this URL:|
Solanki JD, Mehta HB, Shah CJ, Gokhale PA. A study of effect of shift work, sex, and smoking on development of ONIHL in plastic weavers. Indian J Otol [serial online] 2013 [cited 2020 Feb 26];19:1-4. Available from: http://www.indianjotol.org/text.asp?2013/19/1/1/108148
| Introduction|| |
Noise is most insidious and frequent of all occupational hazards.  In the recent past decades, occupational diseases have been recognized as a growing problem around the world. Noise-induced Hearing Loss (NIHL) is the second most common form of acquired hearing loss after age-induced hearing loss (presbycusis) and studies have showed that people exposed to noise level higher than 85 db suffered from NIHL.  In India, occupational permissible limit of exposure for 8 hours of time-weighted average is 90 db.  According to studies carried out by the National Institute of Occupational Health, India, sound pressure levels were found to be very high in various industries of India and average noise level in textile industries was 102-114 db. 
Till date, no definitive treatment of ONIHL is possible once it develops. However, it is entirely preventable.  This can be achieved by using better engineering control measures and by providing protection to the exposed in the form of PPD (Personal Protective Devices) and by administrative control measures like periodic shift rotation and by limiting noise exposure when noise level exceeds 85 db. ,
Even few animal studies have shown that noise exposure of moderate intensity with intermittent quiet periods are less damaging than equal intensity continuous type of noise. , Present day shift working regimes can be tested on human without ethical concerns. Many articles have been published on noise and its effect on hearing but very few touching the area of preventive measures and role of shift working as a potential one. Present study tried to look into this hypothesis by comparing hearing of weavers of textile industries quantitatively by dividing textile weavers into groups based on shift pattern of their working. It also tried to look into the factors like gender, shift pattern, and smoking as a contributory one for hearing loss, the knowledge of which can help to design better preventive measures by work regimes in future.
| Materials and Methods|| |
Present cross-sectional study was carried out in plastic textile weavers after prior approval from Institutional Review Board and taking informed consent from workers. 50 plastic workers (18 females and 32 males) were randomly selected from five different plastic weaving factories who were not exposed to any other occupational hazards like organic solvents and who had no break in job. Sample size was calculated by using software Raosoft keeping confidence interval 95%. Of 64 workers, 14 were excluded during screening due to presence of some other cause of hearing loss apart from noise. Depending upon shift work, they were divided into 3 groups: (1) D I − Interrupted day shift workers working 8 hours with a break of two hours in between 6 days a week, (2) D C - Continuous day shift workers working for 8 hours without any interruption 6 days a week, (3) N − Night shift workers working for 12 hours night shift uninterrupted 5 days a week with two days rest at weekend.
Subjective hearing was assessed by personal questionnaires related to presence/absence and type of hearing loss. Pure tone audiometry was done by investigator himself after getting training for the procedure in ENT department of the institution. Hearing thresholds at various frequencies for air conduction were measured using ALPS manual audiometer. This field study was carried out in a silent room away from the workplace at weekends to avoid temporary threshold shift by allowing at least 16 hours of break from the last exposure. Pure tone average hearing thresholds were compared at low frequencies and high frequencies. Three criteria were used for assessing hearing thresholds: (1) LFH (Low frequency hearing, (500Hz + 1000Hz + 2000Hz)/3), (2) HFH (High frequency hearing, (3000Hz + 4000Hz + 6000Hz)/3), and (3) comparison between 4000 Hz, 6000Hz, and 8000 Hz.
Results were expressed as Mean ± Standard Deviation (95% confidence interval (CI)). Data analysis was accomplished using software GraphPadInStat 3 (demo version). Comparisons between the various groups were done by using unpaired t-test. A P value of less than 0.05 was considered significant.
| Results|| |
In all three groups (D I , D C, N), hearing thresholds at higher frequencies were more than that at lower frequencies, each being statistically significant [Table 1]. Females showed better hearing than age-matched males at 4 kHz and less significantly at 6 kHz, but it proved statistically insignificant [Table 2]. Smokers had higher hearing threshold than non-smokers at 4 and 6 kHz. However, none of these differences proved statistically significant [Table 3]. Within day shift workers, interrupted shift work showed statistically significant better hearing than uninterrupted work. This difference was most significant at 4 kHz, less at 6 kHz, and least at 8 kHz [Table 4]. Amongst continuous shift workers, day shift workers have higher hearing thresholds than night shift workers for which maximum significance was found at 8 kHz followed by 4 kHz and 6 kHz [Table 5].
|Table 1: Effect of type of shift on hearing thresholds (in db) at high and low frequencies|
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|Table 2: Effect of gender on hearing thresholds (in db) at 4 kHz and 6 kHz amongst age-matched workers|
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|Table 4: Hearing thresholds (in db) at 4 kHz, 6 kHz, and 8 kHz amongst interrupted and uninterrupted day shift workers|
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|Table 5: Hearing thresholds (in db) of continuous day shift workers and male night shift workers at 4 kHz, 6 kHz and 8 kHz|
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| Discussion|| |
ONIHL is widespread, irreversible work-related problem in adults, raising felt need for effective hearing conservation program particularly in developing countries like India.  Our study found that various shift workers of plastic weaving industries exposed to industrial noise have in general raised hearing thresholds at higher frequencies than lower (speech) frequencies. This observation is supported by previous such studies  and explains why initially the disease remains symptomless and why day-to-day activity is not affected much.
It was observed that 8-hour day shift workers working 6 days/week had poor hearing than 12-hour night shift workers working for 5 day/week with two days off at weekend. Within day shift workers, an interruption of 2 hours in 8-hour shift led to better hearing in interrupted shift workers than those who worked continuously. Since two groups working consecutive days and with uninterrupted exposure showed more hearing loss, we can infer that the risk of hearing loss is less with intermittent exposure than continuous noise.
A similar observation was found by Chou, et al.  that working with 12 hours shift for two continuous days followed by two days off had significantly lower permanent hearing loss than those working in 9-hour shift for 5 days with weekend off.  Another study proved that noise-exposed three-shift workers had lower average permanent hearing loss than single-shift workers. However, a third study showed no apparent benefit of 12-hour working shift than 8-hour shift.  But this can be due to inadequate audiometry testing procedure. This beneficial effect of shift working can be well understood by animal models. 
Animal studies have shown that ONIHL may be caused by direct mechanical damage or indirect metabolic processes.  Impulse noise after a critical point causes direct mechanical damage to cochlea.  However, the damage is not proportional to total noise energy because intermittent noise causes less damage to cochlea than continuous noise of the same intensity.  Shorter intermittent noise exposure (Like interrupted day shift workers of present study) induces less permanent threshold shift than equal energy noise exposure with longer period and shorter rest in between (Like continuous day shift workers in present study). 
Continuous noise exposure produces free radical insult such that the death of hair cells is accelerated with time after noise exposure for a period of 14 days. Due to its effect on reduction of continuous exposure to noise, it can be hypothesized that noise-induced free radical formation resulted in a significant factor in decreased cochlear blood flow and free radicals formation to alleviate the progressive degree of hearing loss. , Hearing profiles of various shift workers indicate that interrupted day shift workers and to some extent night shift workers have interrupted noise exposure which may lead to smaller Temporary Threshold Shift (TTS) and Permanent Threshold Shift (PTS), comparatively less cochlear damage and better hearing. Even a brief interruption like the one in interrupted day shift workers for 2 hours in 8-hour shift clearly resulted in significantly smaller PTS that can be attributed to less hair cell damage than continuous noise exposure as shown in animal studies. 
In present study, all workers of group D I were females who went to home for 2 hours in lunch break. Female gender has shown better hearing than males like other previous studies.  This can be due to the advantage of 2-hour interruption. Women usually work in spinning section and men in weaving section. As shown by a previous study carried out at Lagos Metropolis, spinning section produces less intense noise than weaving section and workers in the later section have comparatively more hearing loss.  However, in present study, the weaving and spinning section are within the same premises in all plastic weaving factories. So, the difference cannot be attributable to the type of noise but to the interruption in noise exposure.
As in line with previous studies done worldwide, there seems to be a positive correlation between smoking and NIHL. , However, in our study, the disadvantage due to smoking factor is statistically insignificant. Still, smoking should be given up to avoid other health hazards.
Various engineering noise controlling means, , pharmacological studies,  and genetic studies  are future trends for the prevention of ONIHL. However, change in shift pattern of work and introducing a concept of interrupted exposure may be more practical means if properly studied and implemented. It is well established by animal studies that exposure to intermittent noise characteristically produces less damage than equal energy continuous noise. Direct human studies about effect of various types of shift work regimes on NIHL represent a prophylactic potential that warrants further research activity. Studies like the present one might pave the direct use of intermittent noise exposure regimes in future design of noise exposure workday/week making future hearing conservative program even more effective. But, to support this hypothesis, further vivid study with larger sample size is required.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]