European Journal of Cardiovascular Medicine

Diabetes mellitus is a chronic metabolic disorder characterized by high blood glucose levels, primarily resulting from insulin resistance and a relative insulin deficiency. Approximately 5% of the Indian population suffers from this condition. Long-term complications include macrovascular and microvascular issues. Microvascular complications and diabetic neuropathy contribute to hearing impairment in affected individuals. Due to its high metabolic demands, the auditory pathway is particularly vulnerable to the effects of hyperglycemia and diabetes. Existing literature suggests that diabetes-related hearing loss is typically moderate in severity, progressive in nature, and affects both ears. Proposed underlying mechanisms include microangiopathy of the inner ear, neuropathy of the cochlear nerve, and disturbances in endolymphatic potential. 

Several studies have recognized diabetes mellitus as an independent factor causing sensorineural hearing loss. Pure tone audiometry (PTA) is a crucial hearing test that determines hearing thresholds for standardized stimuli via air and bone conduction. This subjective test helps identify the degree, type, and pattern of hearing loss. Earlier studies have documented the prevalence of hearing loss among individuals with diabetes to range between 64% and 72.5%. 

This observational study was conducted over five months, from March to July 2025. 

The participants, aged 35 to 50 years, included 50 individuals with diagnosed type 2 diabetes mellitus attending the outpatient ENT department at the Government ENT Hospital, Visakhapatnam. Fifty non-diabetic, healthy participants were included in the control group. Exclusion criteria included type 1 diabetes, previous ear surgeries, prolonged noise exposure, hypertension, head or ear trauma, ototoxic drug use, family history of deafness, and participant refusal. Informed consent was obtained from all participants after explaining the study in their native language. The study received approval from the Institutional Ethical Committee, Andhra Medical College, Visakhapatnam. 

The study population was divided into two groups: one consisting of 50 subjects diagnosed with type 2 diabetes (Group A), and the other comprising 50 healthy individuals (Group B) matched for age and gender to serve as controls. Glycemic control in the diabetic group was assessed using HbA1c testing. All subjects underwent pure tone audiometry, with air conduction thresholds measured at 250, 500, 1000, 2000, 4000, and 8000 Hz, and bone conduction thresholds recorded at 250, 500, 1000, 2000, and 4000 Hz. Each participant’s hearing threshold was assessed, and any measurement above 25 dB was interpreted as evidence of auditory impairment. The degree of hearing loss was classified according to WHO guidelines (1980): normal (0–25 dB), mild (26–40 dB), moderate (41–55 dB), moderately severe (56–70 dB), severe (71–90 dB), and profound (>90 dB). 

Data analysis: 

Data was tabulated in Microsoft Excel and analyzed using SPSS version 25.0. The data were analyzed by calculating mean values and standard deviations. Student’s t-test was used to compare the hearing threshold between the diabetic group and healthy controls. A p-value of < 0.05 was considered statistically significant. Chi-square test was used to verify the association between the variables.  

In the present study, among 50 subjects in each group, 35 (70%) were males and 15 (30%) were females. 14 subjects were in the age group of 35–45 years and 36 subjects were in the age group of 46–55 years. Overall, the study sample is male predominant (Table 1).   14 subjects (28%) presented with diabetes less than 5 years duration, 16 subjects (32%) presented with 5-10 years duration of diabetes and 20 subjects (40%) presented with more than 10 years duration of diabetes (Table 2).

Among 50 diabetics, 33 (66%) subjects had sensorineural hearing loss and 17 (34%) subjects had normal hearing. Among 50 non-diabetic, healthy subjects, only 2 (4%) subjects had sensorineural hearing loss. A prevalence of 66% of sensorineural hearing loss was found among diabetics compared to 4 % among the non-diabetic control group (Table 3).  

Among 33 diabetics with SNHL, 21.2 % were in 35-45 years age group, 78.7% were in 45-55 years age group (Table 4). 

And 20 diabetic subjects had mild hearing loss, 10 had moderate hearing loss and 3 had moderately severe hearing loss (Table 5).  

Out of 50 diabetics, 32 subjects had HbA1c value <6.5 and 18 subjects had HbA1c value > 6.5. The prevalence of SNHL in diabetics with HbA1c <6.5 was 60.6% while in diabetics with HbA1c > 6.5, it was 39.3%. And on Chi-square test, the association between HbA1c and prevalence of hearing loss among diabetics is not statistically significant (p > 0.05) (Table 6). 

On Chi-square test, there is a highly significant difference (p < 0.0001) in the prevalence of hearing loss between diabetics (66%) and healthy controls (4%) (Table 7).  

On Chi-square test, the association between age group and prevalence of hearing loss among diabetics is not statistically significant (p > 0.05) (Table 8).  

The proportion of patients with SNHL was more with diabetes duration of >10 years (95%), followed by those with 5–10 years (87.5%), and zero (0%) in patients with < 5 years of duration. And On Chi-square test, the association between duration of diabetes and prevalence of hearing loss is statistically significant. (Table 9). 

Table 1:  Distribution of study population according to age and gender

Table 2: Distribution of the diabetic patients according to duration of diabetes

Table 3: Prevalence of SNHL in Diabetics and Controls

Table 4: Prevalence of SNHL in Diabetics according to age group

Table 5: Distribution of diabetics according to degree of hearing loss

Table 6: HbA1c level and Prevalence of SNHL

Table 7: Statistical analysis of Prevalence of Hearing loss in diabetics vs controls

Table 8: Statistical Analysis of effect of Age on prevalence of hearing loss among diabetics

Table 9: Statistical Analysis of effect of duration of Diabetes on prevalence of hearing loss among diabetics

There is a highly significant correlation between longer duration of diabetes and hearing loss (p < 0.00001).

In the current study, 66% of individuals with type 2 diabetes exhibited sensorineural hearing loss, compared to just 4% among non-diabetic healthy controls. This observation is consistent with the outcomes documented by Aggarwal et al. (64.86%)¹² and Rajendran et al. (73.3%)¹³. In contrast, lower rates were reported by Meena R et al. (58%)¹⁴ and Mozaffari M et al. (45%)¹⁵. These variations in prevalence across studies may be attributed to differences in study design, including sample size, duration of study, and the demographic characteristics of the participants, particularly age distribution. In the present investigation, the majority of individuals with diabetes demonstrated mild, bilateral sensorineural hearing impairment. Among these patients, hearing loss progressively worsened across frequencies ranging from 250 Hz to 8000 Hz. Several pathophysiological mechanisms may underlie the observed association. The greater impact on higher frequencies is possibly due to accelerated atherosclerosis and basement membrane thickening, which impair cochlear blood flow and contribute to cellular degeneration and loss of high-frequency hearing¹⁶. Our study also explored the interplay between age, duration of diabetes, and the prevalence of hearing loss. The findings revealed a clear association between longer duration of diabetes mellitus and sensorineural hearing loss (SNHL), with the highest prevalence observed in patients who had diabetes for over 10 years compared to those with a shorter disease history. Among diabetic individuals, SNHL was significantly more common in the 46–55 age group (78.79%) than in the 35–45 age group (21.21%), indicating that the frequency of SNHL increases with advancing age. But the association between age group and prevalence of hearing loss was not statistically significant (p > 0.247). Within the 35–55 age range, age alone does not show a significant impact on the prevalence of hearing loss among diabetic individuals in this sample.   

Our findings are consistent with those of Mitchell et al¹⁷ and Pemmaiah et al¹⁸ who observed a positive correlation between the duration of diabetes mellitus and the development of hearing impairment. Our study found no significant correlation between HbA1c levels and the incidence of hearing loss. Histopathological studies have shown thickening of the capillary walls in the stria vascularis and degeneration of the spiral ganglion cells in diabetic patients, supporting a biological basis for the hearing deficits observed¹⁹. There are some limitations to our study. To begin with, the study was limited by a small sample size; expanding the sample and including participants from diverse geographic regions could have led to more reliable and comprehensive outcomes. Moreover, pure tone audiometry, the diagnostic tool employed to assess hearing loss, is a subjective test that depends on individual patient responses, potentially affecting the consistency of the results. Subclinical hearing loss could not be evaluated. 

The present study found SNHL in 66% of subjects with type II diabetes and in 4% of healthy, non-diabetic individuals. The majority of patients in the study exhibited mild sensorineural hearing loss (SNHL). While the duration of diabetes showed a positive correlation with hearing impairment, neither age nor HbA1c levels appeared to influence hearing status. The risk of hearing loss increases sharply after 5 years of diabetes and is highest in those with more than 10 years duration. A comprehensive audiological assessment is advised for all individuals at the time of diabetes diagnosis. Pure tone audiometry serves as a reliable, non-invasive method for the early identification of hearing impairment in diabetic patients. Routine audiological monitoring should be considered to help improve the quality of life for individuals 

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