Type 2 diabetes mellitus (T2DM) is a major global public health concern, with India currently ranking among the countries with the highest burden ^[1]. Chronic hyperglycemia in T2DM leads to metabolic derangements affecting multiple organs and endocrine axes ^[2]. Thyroid dysfunction (TD) is the most common endocrine disorder coexisting with diabetes, and both conditions influence each other through several hormonal and metabolic pathways ^[3].

The thyroid gland regulates metabolic rate, lipid metabolism, glucose homeostasis, and thermogenesis. Even mild alterations in thyroid function—termed subclinical thyroid dysfunction—can affect insulin sensitivity, lipid metabolism, and cardiovascular function ^[4]. Subclinical hypothyroidism, characterized by elevated TSH with normal free T4, is particularly common in T2DM and is associated with dyslipidemia, endothelial dysfunction, and increased cardiovascular risk ^[5].

Studies across the world have reported varying prevalence of thyroid dysfunction among T2DM patients, ranging from 10% to 46% ^[6–10]. Radaideh et al. (2004) reported 12.5% prevalence of subclinical hypothyroidism in T2DM patients ^[7], while Wang et al. (2017) identified thyroid disease as significantly more common in diabetes compared to the general population ^[8]. Indian data also demonstrate high prevalence, with Gupta et al. reporting 14.6% and Singh et al. reporting 22% thyroid dysfunction in T2DM cohorts ^[9,10].

Mechanisms linking thyroid dysfunction and T2DM include insulin resistance, autoimmune predisposition, alterations in deiodinase activity, and dysregulation of the hypothalamic–pituitary–thyroid (HPT) axis ^[11]. Anti-TPO antibody-mediated autoimmunity further contributes to subclinical hypothyroidism in diabetics ^[12].

Given regional variations and limited data from northeastern India, this study was undertaken to determine the prevalence and pattern of subclinical thyroid dysfunction in T2DM patients attending a tertiary care hospital.

Objectives:

1. To determine the prevalence of subclinical thyroid dysfunction among patients with T2DM.
2. To assess the pattern and distribution of thyroid abnormalities in T2DM.
3. To evaluate the association between thyroid dysfunction and demographic, clinical, and biochemical parameters.

Materials and Methods:

(With continuous reference numbers)

Study Design and Setting

This was a hospital-based cross-sectional observational study conducted at the Department of Medicine, MJN Medical College & Hospital, Coochbehar (West Bengal), a tertiary care center with a large diabetic population [13].

Study Period: April 2024 to January 2025.

Sample Size Calculation

The minimum sample size was calculated using the formula for prevalence studies:
N = Z²pq / d² [14]
Assuming p = 12.4% (previous Indian prevalence) [9], d = 5%, the sample size obtained was 167. A total of 172 patients were included.

Inclusion Criteria

• Adults aged ≥18 years
• Established T2DM as per ADA criteria
• Willing to participate

Exclusion Criteria

• Known thyroid disease or ongoing thyroid therapy
• Pregnancy or gestational diabetes
• Use of drugs influencing thyroid profile (amiodarone, lithium)
• Critically ill patients

Data Collection

A structured proforma recorded:

• Demographics (age, sex)
• Duration of diabetes
• Symptoms
• BMI, waist–hip ratio
• Complications (neuropathy, nephropathy, retinopathy)

Laboratory Investigations

• Thyroid profile: TSH, FT3, FT4 (chemiluminescence)
• Anti-TPO antibodies
• Glycemic profile: FBS, PPBS, HbA1c
• Lipid profile
• Renal parameters: urea, creatinine, ACR

Thyroid dysfunction was classified per ATA Guidelines (2012)

• Subclinical hypothyroidism: ↑TSH, normal FT4
• Subclinical hyperthyroidism: ↓TSH, normal FT3/FT4
• Overt hypo-/hyperthyroidism: abnormal TSH + abnormal FT3/FT4

Statistical Analysis

Data analysis was performed using SPSS version 26. Continuous variables were expressed as mean ± standard deviation (SD), while categorical variables were presented as frequencies and percentages. Associations between categorical variables were assessed using the Chi-square test, and a p-value < 0.05 was considered statistically significant.

Results & Analysis:

Table 1. Baseline Demographic Characteristics of Study Participants (n = 172)

Most participants belonged to the 56–70-year age group (64%), followed by 40–55 years (25%), and only 11% were above 70 years. Females constituted nearly two-thirds of the study population (64.5%), and a substantial proportion of participants were either primary educated (34.3%) or illiterate (32%).

Table 2. Clinical Profile Related to Diabetes (n = 172)

Around 38.4% of the participants had diabetes for more than 10 years, and more than half (55.8%) were on oral hypoglycaemic agents alone, while 24.4% required both insulin and OHA. Overall, glycaemic control was poor in the cohort, with 67.4% having uncontrolled HbA1c ≥7%.

Table 3. Thyroid Status of Study Participants (n = 172)

Subclinical hypothyroidism was the most common thyroid abnormality, affecting 32.6% of participants, followed by overt hypothyroidism (14.5%). Only 44.2% of the population were euthyroid, indicating a high burden of thyroid dysfunction among T2DM patients.

Table 4. Association Between Age and Thyroid Dysfunction (n = 172)

χ² = 3.7, p = 0.43 (NS)

Although thyroid dysfunction appeared slightly more frequent in ≥60-year individuals, with 32.2% having subclinical hypothyroidism, the association between age group and thyroid status was statistically insignificant (p = 0.43).

Table 5. Gender-wise Distribution of Thyroid Dysfunction (n = 172)

χ² = 5.67, p = 0.0173 (Significant)

Thyroid dysfunction differed significantly between genders (p = 0.0173). Females predominantly exhibited subclinical hypothyroidism (33.3%), whereas males showed higher rates of subclinical hyperthyroidism (13.1%).

Table 6. Association Between Duration of Diabetes and Thyroid Dysfunction (n = 172)

χ² = 10.75, p = 0.0046 (Significant)

A strong association was observed between increasing duration of diabetes and thyroid dysfunction (p = 0.0046). Participants with diabetes ≥10 years had the highest proportion of subclinical hypothyroidism (51.5%), whereas those with <5 years duration showed minimal thyroid abnormalities.

Table 7. Glycaemic Control vs Thyroid Status (n = 172)

χ² = 41.81, p < 0.000001 (Highly Significant)

Poor glycaemic control (HbA1c ≥7%) was markedly more common among participants with hypothyroid states, particularly overt (100%) and subclinical hypothyroidism (89.3%), demonstrating a highly significant association between glycaemic status and thyroid dysfunction (p < 0.000001).

Table 8. Microvascular Complications vs Thyroid Status (n = 172)

χ² = 28.59, p < 0.00001 (Significant)

Microvascular complications were more prevalent among hypothyroid patients, affecting 92% of overt and 89.3% of subclinical hypothyroid individuals, compared with 53.9% of euthyroid participants. This association was statistically significant (p < 0.00001).

Table 9. Macrovascular Complications vs Thyroid Status (n = 172)

χ² = 28.22, p = 0.00001 (Significant)

Macrovascular complications were also significantly higher in hypothyroid states, particularly overt hypothyroidism (84%) and subclinical hypothyroidism (55.4%). All participants with subclinical hyperthyroidism exhibited macrovascular involvement, indicating a strong association (p = 0.00001).

Table 10. Lipid Abnormalities (Dyslipidemia) in Relation to Thyroid Status (n = 172)

χ² = 22.71, p < 0.0001 (Highly Significant)

Dyslipidemia prevalence was strikingly higher among those with thyroid dysfunction, affecting 89.3% of subclinical hypothyroid and 100% of overt hypothyroid participants, while only 40.8% of euthyroid individuals had lipid abnormalities, showing a highly significant association (p < 0.0001).

Discussion:

In the present study, thyroid dysfunction was observed in 55.8% of patients with type 2 diabetes mellitus, with subclinical hypothyroidism being the most common subtype (32.6%). This prevalence is higher than that reported by Han et al. (2015) ^[13], who found a pooled prevalence of 10.2% among T2DM patients, and also higher than the findings of Kahaly & Frommer (2018) ^[14], who reported thyroid dysfunction in 28–35% of diabetics. However, our prevalence closely resembles that of Yaseri et al. (2025) [15], who reported thyroid dysfunction in 61.9% of diabetic individuals.

A significant association was observed between female gender and thyroid dysfunction in our study, consistent with Jali et al. (2017) ^[16], who found a significantly higher prevalence of hypothyroidism and subclinical hypothyroidism in diabetic women. We also found that thyroid dysfunction increased with longer duration of diabetes, which aligns with Khandelwal & Tandon (2012) ^[17], who suggested that chronic metabolic stress and insulin resistance may predispose diabetic patients to thyroid abnormalities.

Poor glycaemic control (HbA1c ≥7%) was more prominent among those with hypothyroid states, mirroring the findings of Mohamed et al. (2017) ^[18], who reported worse metabolic control in diabetic patients with thyroid dysfunction. Similarly, the strong association between dyslipidemia and hypothyroid states in our study agrees with Elhussein et al. (2025) ^[19], who demonstrated that subclinical hypothyroidism significantly worsens lipid profile and increases cardiovascular risk in diabetics.

Regarding complications, microvascular and macrovascular complications were more common among patients with hypothyroidism, which is consistent with the meta-analysis by Han et al. (2015) ^[13], who reported increased risks of nephropathy, retinopathy, and neuropathy in SCH patients. Conversely, some authors such as Chaker et al. (2014) ^[20] did not find significant differences in complication rates between euthyroid and SCH diabetics, indicating heterogeneity across populations.

Conclusion

In this study, more than half of the patients with type 2 diabetes mellitus exhibited thyroid dysfunction, with subclinical hypothyroidism being the most prevalent abnormality. Thyroid dysfunction was significantly associated with female gender, longer duration of diabetes, poor glycaemic control, dyslipidemia, and a higher burden of both microvascular and macrovascular complications. These findings highlight the clinical importance of routinely assessing thyroid function in patients with T2DM, particularly those with uncontrolled diabetes or long-standing disease. Early detection and management of thyroid dysfunction may contribute to improved metabolic control and a reduction in diabetes-related complications.

References:

1. Sapra A, Bhandari P. Diabetes. [Updated 2023 Jun 21]. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. 2025.Available from: https://www.ncbi.nlm.nih.gov/books/NBK551501/
2. International Diabetes Federation. Diabetes Atlas, 6th edn. 2013, p. 30,34.
3. American Diabetes Association (ADA): Introduction:Standards of Medical Care in Diabetes—2021. Diabetes Care 1 January 2021; 44 (Supplement_1): S1–S2. Available from: https://doi.org/10.2337/dc21-Sint
4. Saeedi P, Petersohn I, Salpea P, Malanda B, Karuranga S, Unwin N, Colagiuri S, Guariguata L, Motala AA, Ogurtsova K, Shaw JE. Global and regional diabetes prevalence estimates for 2019 and projections for 2030 and 2045: Results from the International Diabetes Federation Diabetes Atlas,9^th Diabetes research and clinical practice. 2019 Nov 1; 157:107843.
5. Harding JL, Pavkov ME, Magliano DJ, Shaw JE, Gregg EW. Global trends in diabetes complications: a review of current evidence. Diabetologia. 2019 Jan;62(1):3-16.
6. DeFronzo RA, Ferrannini E, Groop L, Henry RR, Herman WH, Holst JJ, Hu FB, Kahn CR, Raz I, Shulman GI, Simonson DC. Type 2 diabetes mellitus. Nature reviews Disease primers. 2015 Jul 23;1(1):1-22.
7. Duntas LH, Brenta G. A renewed focus on the association between thyroid hormones and lipid metabolism. Frontiers in endocrinology. 2018 Sep 3; 9:511.
8. Papazafiropoulou A, Sotiropoulos A, Kokolaki A, Kardara M, Stamataki P, Pappas S. Prevalence of thyroid dysfunction among greek type 2 diabetic patients attending an outpatient clinic. Journal of clinical medicine research. 2010 Mar 25;2(2):75.
9. Biondi B, Kahaly GJ, Robertson RP. Thyroid dysfunction and diabetes mellitus: two closely associated disorders. Endocrine reviews. 2019 Jun;40(3):789-824.
10. Shabnam S, Mallikarjuna CR, Pinjar PM. Study of subclinical hypothyroidism among patients with type 2 diabetes mellitus. Journal of Clinical and Scientific Research. 2015 Jul 1;4(3):195-8.
11. Taylor PN, Albrecht D, Scholz A, Gutierrez-Buey G, Lazarus JH, Dayan CM, Okosieme OE. Global epidemiology of hyperthyroidism and hypothyroidism. Nature Reviews Endocrinology. 2018 May;14(5):301-16.
12. Javeedh S, Vidya TA. Study of subclinical thyroid disorders in type 2 diabetes mellitus. J Evid Based Med Healthc 2021;8(02):103-107.
13. Han C, He X, Xia X, Li Y, Shi X, Shan Z, et al. Subclinical hypothyroidism and type 2 diabetes: A systematic review and meta-analysis. PLoS One. 2015;10(8):e0135233.
14. Kahaly GJ, Frommer L. Polyglandular autoimmune syndromes in diabetes. Lancet Diabetes Endocrinol. 2018;6(11):874–85.
15. Yaseri M, Farrokhi S, Hosseini MS, Shafiee A, Abdollahi A. Prevalence and predictors of thyroid dysfunction among patients with type 2 diabetes mellitus: A large observational study. Diabetes Metab Syndr. 2025;19(1):102–10.
16. Jali MV, Kambar S, Jali SM, Hiremath MB, Nalawade P. Prevalence of thyroid dysfunction among type 2 diabetes mellitus patients in a tertiary care hospital, Vijayapura, Karnataka. J Clin Diagn Res. 2017;11(8):OC36–8.
17. Khandelwal D, Tandon N. Overt and subclinical hypothyroidism: Who to treat and how. Indian J Endocrinol Metab. 2012;16(2):238–46.
18. Mohamed GA, El Saied AR, El-Masry SA. Thyroid dysfunction in type 2 diabetes mellitus and its relation to glycaemic control. Alexandria J Med. 2017;53(3):227–31.
19. Elhussein AB, Abdalla AI, Hassan MA, Elbashir LF, Fadlelmola HA, Musa IR, et al. Impact of hypothyroidism on lipid profile and cardiovascular risk among patients with type 2 diabetes: A cross-sectional study. Sci Rep. 2025;15:4452.
20. Chaker L, Bianco AC, Jonklaas J, Peeters RP. Hypothyroidism. Lancet. 2017;390(10101):1550–62.