European Journal of Cardiovascular Medicine

Type  2  diabetes  mellitus  (T2DM)  or  non-insulin  dependent  diabetes  (NIDD)  is  the  most prevalent  form  of  diabetes  caused  due  to  either  impaired  secretion  of  insulin  or  insulin resistance or both.[1]  As of 2015, an estimated 415 million people had diabetes worldwide,[2] with  type  2  DM  making  up  about  90%  of  the  cases.[3,4]  This  represents  8.3%  of  the  adult population, with equal rates in both women and men. Diabetes is fast gaining the status of a potential epidemic in India with more than 62 million diabetic individuals currently diagnosed with the disease.[5] In 2000, India (31.7 million) topped the world with the highest number of people  with  diabetes  mellitus  followed  by  China  (20.8  million)  with  the  United  States  (17.7 million)  in  second  and  third  place  respectively.  It  is  predicted  that  by  2030  diabetes  mellitus may  affect  up  to  79.4  million  individuals  in  India,  while  China  (42.3  million)  and  the  United States (30.3 million) will also see significant increases in those affected by the disease.[6,7]

Macroangiopaties due to accelerated atherosclerosis in the minor blood vessels due to thickening  of  the  basement  membrane  is  the  major  cause  of  all  long  term  and  widespread diabetic complications. Micro and macro-vascular complications leading to nephropathy, retinopathy, neuropathy, hearing impairment, myocardial infarction and stroke are the major cause of morbidity and mortality due to long term diabetes mellitus.[8] .As far as the auditory complications  are  concerned,  angiopathy 

May interfere with blood supply to the cochlea by directly reducing transport through the thickened walls of capillaries, and indirectly by the reduction of flow in vascular pathways, because of secondary degeneration of 8th cranial nerve due   to   diabetic   neuropathy.    In    addition    to    it,   there    is    also    a    progressive    degenerative involvement   of   the   Nervous   system   in   the   form   of   peripheral   neuropathies   and   other   organ based neuronal   impairment.   Data    suggest    that    almost all patients    worldwide    have    a  prevalence of auditory impairment in type 2 DM.

However, there are different opinions about  the  clinical    and  biochemical  consequences  of pathological affections caused in the auditory system by type 2 DM.(2)The characteristic finding in  Diabetes  Mellitus  is  a  bilateral  symmetrical  sensorineural  hearing  loss  particularly  at   the higher  frequencies  of  sound.  Although most workers  suggested  that  hearing  impairment seemed  to  be  dependent  upon  the  severity  and  duration  of  diabetes  others  did  not  find any association between hearing loss and diabetes. Hence, we considered that there are inconclusive evidences regarding development of sensorineural hearing loss in type 2 DM in our population also as few studies are available till now in this field. Keeping these facts and lacunae in the present state of knowledge it was hypothesized that severity  of  hearing  loss  is  associated  with  the  degree  of  insulin  resistance  in  type  2  diabetes mellitus.

2.1 Study Area

This hospital based, case-control, observational cross-sectional study was conducted in the Department of ENT with the collaboration of Department of Biochemistry of Calcutta National Medical College &Hospital, Kolkata West Bengal, India.

2.2 Ethics Statement

The study was approved and permitted by the institutional ethics committee for care and use of laboratory and started after obtaining the written consent from the concerned ethics committee.

2.3 Study population

The present study was conducted between March 2021 and August 2022. Sample size was calculated at 95% confidence interval, with a power of 80% [9] using the formula N = 2{(Zα + Zβ)²σ²}/d²

150 patients (cases) aging between 18 and 45 years old and of both sexes with sensorineural hearing disorder diagnosed by pure tone audiometry were included in the study. In addition, 200 healthy persons with any type of hearing loss of the same ages and sexes were included in this study as a control group from same region. Both the cases and controls were selected by a simple random method. Every patient was informed about the details of the study through individual interviews and all the provided written informed consent. Information regarding age, gender, Body mass index (BMI), type and duration of intake of hypoglycaemic agents, self-reported dietary and drug compliance were gathered.  All the study population was strictly followed the Diabetic diet [10] and none of them were affected by any infection nor taken any medication that affects the glycemic status of the subject atleast 6 months. Patients with cancer, history of pre-existing musculoskeletal disease, chronic disease of liver, kidney, and heart are not included in this study. Pregnant and lactating women, persons on immunosuppressive drugs for another disease were excluded from the study.

Then cases were grouped into two groups depending upon severity of sensorineural deafness-

Group I (n = 75) with mild sensorineural deafness.

Group II (n =75) with severe sensorineural deafness

2.4Collection of Samples

Peripheral venous blood was drawn from all participants after 12 hours fasting and the samples were divided into three aliquots. The first one was collected in oxalate and fluoride vial for obtaining plasma for fasting glucose estimation as well as in the postprandial state two hours after lunch) on the same day, second one in EDTA containing vial for HbA1C assays and third one in clotted vial for lipid profile.

2.5 Estimation of Plasma Glucose Level 

It was estimated by glucose oxidase-peroxidase enzymatic method using span diagnostic kit as per the manufacturer’s instructions [11] by completely automated clinical chemistry analyzers – ERBA XL-600 after usual daily calibration and ensuring quality performance before starting analysis and the samples were analyzed along with the other routine samples. Intraassay CV% was 1.2% and interassay CV% was 2.1%. Qualitative detection of glucose in urine was accomplished by Benedict’s test. Acceptable control level of blood glucose were defined as FBS value equal or less than 110 mg/dl and PPBS value equal or less than 126 mg/dl.

2.6 Estimation of plasma HbA1C

Using commercially available Hemoglobin A1C kit supplied by Siemens Company did Hemoglobin A1C test. It implies the principle of turbidimetric inhibition immunoassay (TINIA). [12,13] This company also supplied total Hb kit for estimation total Hb by alkaline hematin method. 

2.7 Anthropometric Measurements

Weight and height measurements were obtained, usingstandardized technique.[14] BMI was calculated as the weight in kilograms divided by the square of height in meters.

2.8 Serum insulin assay

Serum insulin was assayed by ELISA kit AccuBind from Monobind Inc. USA. Both the inter- and intra-assay CVs were below 3%.[15,16] No cross reactivity with C-peptide was detected.

2.9 Insulin sensitivity measurement

Homoeostatic model assessments (HOMA) of steady state β cell function (% β), insulin sensitivity (% S) and insulin resistance (HOMA IR) is computed with the formula that is fasting plasma glucose (mmol/l) times fasting serum insulin (mIU/l) divided by 22.5.[17]

2.10 Lipid profile assay

Among the lipid profile serum total cholesterol, triglyceride (TG) and high density lipoprotein (HDL) were assayed by Cholesterol Oxidase–peroxidase (CHOD–PAP), glycerol-3-phosphate oxidase (GPO), polyanion precipitation methods respectively using semi-auto analyser. Serum very low-density lipoprotein (VLDL) was calculated by dividing the value of TG by 5 and serum LDL was obtained by Friedwald equation.[18]

2.11Pure-Tone Audiometry

In the cases pure-tone audiometry was used to evaluate hearing deficits by spot-checking certain frequencies, or to evaluate deficits more completely.

Testing should begin at 1,000 Hz, because this frequency is easily heard by most patients and has the greatest test-retest reliability. A common frequency sequence for pure-tone threshold search testing is to test at 1,000, 2,000, 3,000, 4,000, 8,000, 1,000 (repeat), 500, and 250 Hz. Sound frequency (ranging from low to high pitch) is recorded on the audiogram's horizontal axis. Sound intensity is recorded on the vertical axis. Right ear thresholds are manually recorded as a red circle on the audiogram. Left ear thresholds are manually recorded as a blue X.

2.11 Statistical Analysis

Data obtained were analyzed for normal distribution using Kolmogrov Smirnoff Statistical test. Then the data for biochemical analysis was subjected to standard statistical analysis using the Statistical Package for Social Science

(SPSS) 27 software for windows. biochemical analysis was subjected to standard statistical analysis using the Statistical Package for Social Science 

3.1 The characteristics and their comparison among different groups of study population – Chi-square test

Baseline personal profile and clinical details of the study population are not statistically significant as shown in Table 1. It indicates that controls are age, sex and demographically matched with cases. It is also shown that cases have followed the ATP criteria but there is no renal insufficiency as well as liver complication among cases.

  Table 1: Personal profile and clinical details and their comparison among different groups of study population

   Data are expressed as numbers (group percentages in parentheses) for categorical variables and mean values ± SD for continuous variables

3.2Comparison of HOMA IR and plasma level of FBS and PPBS between cases and control group – Unpaired t test Fasting blood glucose in Group 1 (mild sensorineural deafness group) shows mean 123.68 mg/dl with standard deviation 11.35 and in group 2 (severe SN Deafness) shows mean 171.17 mg/dl with standard deviation 49.22 than control which shows mean 100.30.mg/dl with standard deviation 24.63.

About the HOMA IR, mean value in Group 1 is 1.85 with standard deviation 0.64 and mean of in Group 2 is 7.52 with

standard deviation 2.29 than mean in Control is 2.13 with standard deviation 0.87.

Table 2: The differences in the HOMA IR and plasma levels of FBS, PPBS in sensorineural deafness patients and control group

Data are expressed as mean values ± SD

3.3Comparison of HOMA IR and plasma level of FBS, PPBS between the groups within the cases group - Independent Samples Test (t test)

The mean of HOMA IR and plasma level of FBS, PPBS are significantly increased statistically with disease severity [Table 4].

Table 4: Differences in the HOMA IR and plasma levels of FBS, PPBS in cases according to the severity of disease

Initially we tested the difference between FBG & HOMA IR in mild and severe sensorineural deafness groups, result showed that both are significantly higher in severe group as indicated by p value.

Box plots showing distribution of FBG level among the mild and severe sensorineural deafness group. FBG among group I (mild cases) shows normal distribution, whereas FBG in group II (severe cases) is not distributed normally as per box plot.(Figure 1)

Figure 1: Box plots showing distribution of FBG level among the mild and severe sensorineural deafness group.

Then Box plot showing the distribution of HOMA IR among the mild and severe SN Deafness groups.

Figure 2: Box plot showing the distribution of HOMA IR among the mild and severe SN Deafness groups

To further analyze the difference between individual cases Post Hoc Anova was done with Bon Ferroni correction. (Table 5)

Diabetes mellitus is a genetically determined metabolic disorder associated with absolute or relative impairment of insulin and in complete clinical manifestation is characterized by metabolic affections, vascular and neuropathic complications. The main objective of treating patients with diabetes is the prevention of chronic complications because the disease is not curable but only controllable. Incidence of chronic complications of diabetes is quite high. It is estimated that there are five million subjects with diabetes and half of them are not aware of the diagnosis. A large number of subjects, especially children and adolescents, have diagnosis of diabetes made in face of complications, especially infections .One of the morphological aspects more constant in diabetes mellitus is diffuse thickness of basal membrane, which may also happen with vascular endothelium, and it is named diabetic microangiopathy. It is more evident in skin capillaries, skeletal muscles, retina, renal glomeruli, and renal medulla. Its pathogenesis is still obscure, but it is clearly associated with hyperglycemia. Other morphological affections refer to impairment of both motor and sensorial nerves of lower limbs, characterized as Schwann cell lesions, degeneration of myelin and axon damage.

The cause of neuropathy is still very controversial, and it may be related with diffuse microangiopathy that would affect nourishment of peripheral nerves .Neuropathy and angiopathy are common affections in diabetes mellitus. Angiopathy has been observed in small arteries and skin capillaries, muscle, kidney, retina and peripheral nerves. The factors that may cause neuropathy are metabolic disorders (glucose metabolism, lipid metabolism defects and vitamins). Some researchers referred to the fact that vascular affections in interfascicular or intrafascicular branches of vasonbervorum contribute to neuropathy. Atherosclerosis, however, very common in diabetes mellitus, can also contribute to neuropathy, owing to interference in rate of nutrient transfer .Angiopathy may occur both in direct way, interfering with supply to the cochlea by reducing transport through the thickened walls of capillaries, and indirectly by the reduction of flow in vascular pathways, or still, because of secondary degeneration of 8th cranial nerve. Thus, an overall   degenerative process   affects   the   microvasculature   of   the   hearing   apparatus,   the   cochlea   and   the   cochlear nerve leading to substantial loss of   cochlear neurons.

Prolonged   exposure   to   hyperglycemia   is   considered   as   the   major   factor   for   the   various complications in the pathogenesis of diabetes due to sustained glucotoxicity. Despite   the   gravity   of   this   hearing   impairment   as   reported   in   most   cases,   which   has   been associated   with   a   severe   socioeconomic   stigmata,   its   management   has   been   traditionally ignored, specially so when it is a part of a generalized metabolic degenerative disorder such as diabetes  amongst  others,  where  the  management  of  the  disorder  itself  takes  preference  over the   management   of   the   hearing   impairment.   It   thus,   compels   the   treating   physician   to recognize   the   cause   and   site   of   hearing   impairment   and   to   treat   patients   by   knowing   their clinical   profile   in   this   part   of   the   country   and   to   rehabilitate them.

Limitation of the Study

Significant alteration of FBG among sensorineural deafness cases from normal control. Then in comparison of FBG and HOMA IR there is significant difference between mild and severe deafness. FBG & HOMA IR is significantly high in cases with severe deafness than with mild deafness. So from this present study it can be hypothesized that FBG and HOMA IR were significantly high in severe SN Deafness in comparison with control group but there is not significant variation in between control and mild SN Deafness. This could be explained by the cumulative effects of advanced glycation end products and their effects on the inner ear. Screening of all patients with diabetes for hearing loss in a multicentric longitudinal study in future may provide a clearer understanding of the relationship between diabetes and hearing loss

Conflicts of interest

The author declares no competing interest.

Financial burden

Cost for further investigations were borne by the authors on equal share basis and no additional expense were incurred by the participants for the tests. In case the patient needs to travel for such testing, the actual cost incurred was borne by the authors on a case – to case basis.

Ranadhir Sarkar¹, Arindam Samaddar², Suparna Datta³, Subinay Datta⁴*, Anindya Dasgupta⁵

Authors' contributions

Dr (Prof) Anindya Dasgupta⁵participated in the conception and design of the experiments, in the acquisition, analysis and interpretation of data, and was involved in drafting the manuscript. Suparna Datta performed the immunoassays. Subinay Datta participated in the analysis and interpretation of data and performed the statistical analysis. Subinay Datta participated in the analysis and interpretation of data. Ranadhir Sarkar participated in the recruitment of patients and the acquisition of data. Arindam Samaddar participated in the interpretation of data, revising the manuscript for intellectual content and giving the final approval of the version to be published. All authors read and approved the final manuscript. 

1. Misra A. Vikram NK. Insulin resistance syndrome (metabolic syndrome) and obesity in Asian Indians: evidence and implications. Nutrition 2004; 20:482-491. PMID: 15105039 DOI: 1016/j.nut.2004.01.020
2. Williams textbook of endocrinology (12th ed.). Philadelphia: Elsevier/Saunders. pp. 1371–1435. ISBN 978-1-4377-0324-5.
3. Shi Y, Hu FB (7 June 2014). "The global implications of diabetes and cancer. 2014 Jun 7;383(9933):1947-8. PMID: 24910221 DOI: 10.1016/S0140-6736(14)60886-2
4. Vos T, Flaxman AD, Naghavi M, Lozano R, Michaud C, Ezzati M, Shibuya K, Salomon JA, Abdalla S, Aboyans V, et al. (Dec 15, 2012). "Years lived with disability (YLDs) for 1160 sequelae of 289 diseases and injuries 1990–2010: a systematic analysis for the Global Burden of Disease Study 2010." 2012 Dec 15;380(9859):2163-96.  doi: 10.1016/S0140-6736(12)61729-2.
5. Kumar A, Goel MK, Jain RB, Khanna P, Chaudhary V. India towards diabetes control: Key issues. Australas Med J. 2013;6(10):524–31. PMCID: PMC3821052  PMID: 24223071 doi: 4066/AMJ.2013.1791
6. Wild S, Roglic G, Green A, Sicree R, King H. Global prevalence of diabetes-estimates for the year 2000 and projections for 2030. Diabetes Care. 2004;27(3):1047–53. PMID: 15111519 DOI: 2337/diacare.27.5.1047
7. Whiting Dr, Guariguata L, Weil C, Shawj. IDF Diabetes atlas: Global estimates of the prevalence of diabetes for 2011 and 2030. Diabetes Res Clin Pract. 2011;94:311–21. PMID: 22079683 DOI: 1016/j.diabres.2011.10.029
8. Brownlee M. Biochemistry and molecular cell biology of diabetic complications. Nature 2001; 414: 813-820.
9. Szarpak L, Ruetzler K, Safejko K, Hampel M, Pruc M, Kanczuga-Koda L Krzysztof Jerzy FilipiakKJ,  Jaguszewski   Lactate dehydrogenase level as a COVID-19 severity marker. Am J Emerg Med 2021;45:638–639. PMID: 33246860 PMCID: PMC7666711 DOI: 10.1016/j.ajem.2020.11.025
10. Viswanathan M, Mohan V. Dietary Management of Indian Vegetarian Diabetics. Bulletin of the nutrition foundation of India, 1991; 12(2):1-2.
11. Sacks DB, Bruns DE, Goldstein DE, Maclaren NK, McDonald JM, Parrott M. Guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus. Clin. Chem. 2002; 48: 436-472.
12. Hoelzel W, Weykamp C, Jeppsson JO, Miedema K, Barr JR, Goodall I, Hoshino T, John WG, Kobold U, Little R, Mosca A, Mauri P, Paroni R, Susanto F, Takei I, Thienpont L, Umemoto M, Wiedmeyer HM. IFCC reference system for measurementof hemoglobin A1c in human blood and the national standardization schemes in the United States, Japan, and Sweden: a method-comparison study. Clin Chem. 2004; 50(1): 166-174.
13. Geistanger A, Arends S, Berding C, Hoshino T, Jeppsson JO, Little R, Siebelder C, Weykamp C. Statistical methods for monitoring the relationship between the IFCC reference measurement procedure for hemoglobin A1c and the designated comparison methods in the United States, Japan, and Sweden. Clin Chem. 2008; 54(8): 1379-1385.
14. Deepa M, Pradeepa R, Rema M, et al. The Chennai Urban Rural Epidemiology Study (CURES): Study design and Methodolgy (Urban component) CURES-1 J Assoc Physicians India, 2003; 51:863-70.
15. Even MS, Sandusky CB, Barnard ND, et al. Development of a novel ELISA for human insulin using monoclonal antibodies produced in serum-free cell culturemedium. Clin Biochem 2007;40:98-103. http://dx.doi.org/10.1016/j.clinbiochem.2006.10.004
16. Morris ER, Dinesen B, Burnett MA, et al. A new ELISA for specific insulin measurements in type II diabetic patients. Biochem Soc Trans 1993;21:25S.
17. Francisco G, Hernandez C, Galard R, et al. Usefulness of homeostasis model assessment for identifying subjects at risk for hypoglycemia failure during the insulin hypoglycemia test. J Clin Endocrinol Metab 2004;89:3408-12. http://dx.doi.org/10.1210/jc.2003-031883
18. McPherson RA, Pincus MR. Henry’s clinical diagnosis and management by laboratory methods. 21. New Delhi: Elsevier; 2007. p. 209.