Hypothyroidism is one of the common endocrine disorders. This refers to inadequate synthesis of thyroid hormones - triiodothyronine (T3) and thyroxine (T4) by the thyroid gland or inadequate stimulation of the thyroid gland by the pituitary or hypothalamus (1). The inadequate synthesis of thyroid hormones by the thyroid gland is termed as primary hypothyroidism, which accounts for 99 % of all hypothyroid cases, while the failure of stimulation of the thyroid gland by the hypothalamus or pituitary is called central hypothyroidism, which is about one percent (2).  Hypothyroidism is common in any age group, but it is more common in adulthood and middle age. The prevalence is about 11% in India, while it is five percent in western countries. The prevalence shows gender specificity, as females are more affected than males in the six-to-one ratio, and middle-aged and elderly women are much more affected (3,4). The major causes of primary hypothyroidism are iodine deficiency in the diet, Hashimoto's thyroiditis (chronic lymphocytic thyroiditis) due to the production of autoantibodies against thyroperoxidase (anti-TPO) and thyroglobulin (anti-Tg) (5).  The other causes include postpartum thyroiditis, surgical removal of the thyroid gland, radioiodine thyroid ablation, and medication like amiodarone and lithium (6). Thyroid is the major endocrine gland which exerts different metabolic functions through its biologically active form T3. For example, thyroid hormones regulate the basal metabolism, thermogenesis, growth and development as well as many cellular processes. In hypothyroidism, these functions are severely affected and can cause complications in various organs of the body, which in turn affect overall health. The clinical presentations are due to sluggish metabolism, which leads to weight gain, fatigue, constipation, dry skin, cognitive impairment, slowed heart rate, intolerance to cold, and depression (7). As far as depression is concerned, it is significant among hypothyroid women as they show substantial deterioration of their mental health with depression, anxiety, and diminished self-confidence (8).

Trace elements like iodine, iron, selenium, and zinc are essential for normal thyroid hormone metabolism (9). Iodine plays a major role in thyroid hormone synthesis by the process of iodination of tyrosyl residues on thyroglobulin and this process is called organification (10). Iron is a component of thyroperoxidase (TPO) which plays a key role in catalyzing the oxidation of iodide (I-) to iodine (I+), incorporation of iodine on to tyrosyl residue of thyroglobulin to monoiodo tyrosine (MIT), diiodotyrosine (DIT) and subsequent coupling of MIT and DIT forming T3 and T4 (11). Selenium in the selenoproteins of glutathione peroxidase and thioredoxin reductase maintains the redox state for thyroid hormone synthesis and protects the thyroid gland from oxidative stress by hydrogen peroxide. It is also a component of iodothyronine deiodinases. These enzymes are responsible for the conversion of biologically less active T4 to biologically active T3 by deiodination (12). Zinc is essential for the synthesis of thyroid hormones, the binding of T3 to its nuclear receptor and hence its actions on target tissues. It plays a key role in regulating the activity of iodothyronine deiodinases, synthesis of thyroid releasing hormone and thyroid stimulating hormone (13).  The present study assessed the levels of ferritin for the status of iron in hypothyroidism. Ferritin is an intracellular iron-binding protein. It exists in the extracellular compartment as well. Iron-free form refers to an apoprotein that is composed of two subunits, namely H and L (14). Free iron is toxic to cells as it generates free radicals. Therefore, it is complexed with apoprotein and stored as ferritin. Iron in ferritin can be released when there is a need, and its level corresponds to iron stores. Hence, serum ferritin is the most convenient laboratory test for iron status (15, 16). Serum ferritin concentrations are the most employed for determining iron deficiency, as serum ferritin levels usually decline a lot before iron levels decline in iron deficiency. In other words, low serum ferritin concentrations reflect a state of iron depletion (17).  Several scientific studies reported that serum ferritin levels were altered and demonstrated a negative correlation with hypothyroidism, indicating that serum ferritin levels are associated with thyroid function. However, its clinical utility is not fully explored in hypothyroidism.  Therefore, the aim of the present study was to assess serum ferritin levels and their clinical utility in hypothyroidism.

The present study was a hospital-based case-control study. It was carried out in the Departments of Biochemistry and Medicine, Saveetha Institute of Medical College and Hospital, Chennai, India from April 2022 to August 2022. The study was approved by the Institutional Review Board and informed consent was obtained from each study subject.

Study Subjects

A total of 55 hypothyroid subjects (cases; n=55) who attended the outpatient (OP) clinics of the Department of Medicine were recruited for the present study after satisfying the inclusion and exclusion criteria. Among the cases, there were five males (9.10 %) and 50 females (90.90 %).   An additional 55 healthy, age-matched volunteers were also recruited as controls (controls; n=55) that included 11 (20 %) males and 44 (80 %) females. Inclusion criteria: Subjects having hypothyroidism confirmed with serum TSH levels greater than 10.0 μIU/mL. Subjects of both genders in the age group of 20 to 65 years. Exclusion criteria: Subjects with a history of acute illness, diabetes mellitus, obesity, cardiac, liver, and renal diseases, hypertension, thyroid hormone replacement therapy, recent blood transfusion, severe anemia (hemoglobin levels less than 7 gm/dl), iron therapy and medication that interfered with thyroid functions (lithium, antiepileptic drug) or alters serum ferritin level (steroid, oral contraceptive pills) were excluded. Pregnant women were also excluded from the present study.

Sample Collection and Analysis

About five ml of venous blood was collected by venipuncture from an antecubital vein in a vacutainer containing clot activator. The blood samples were allowed to clot, and the serum was separated by centrifuging at 3000 rpm for 15 min and used for thyroid hormone and ferritin assays. Serum free T3 and free T4 levels were analyzed using competitive chemiluminescent immunoassay (CLIA) in Vitros Eci-5600. The values for free T 3 are expressed as pg/ml while for free T4 as ng/dl.  Serum TSH and ferritin levels were analyzed using sandwich CLIA in Vitros Eci-5600. The values for TSH are expressed as µIU/ml while for ferritin as ng/ml.

STATISTICAL ANALYSIS

Analysis of statistical data was performed using SPSS software (Statistical Package for the Social Sciences, version 23, SPSS Inc, Chicago, III, USA). Data were analyzed using an independent student’s t - test for their level of significance. Results were expressed as mean ± SD. The results were considered statistically significant if the p-values were 0.05 or less.

Table 1 shows the outcome of the present study. It shows the mean concentrations of free T3, freeT4, TSH and ferritin among cases (n=55) and controls (n=55). The mean concentration of free T3 was significantly reduced among cases when compared with controls (p < 0.001). The mean concentration of free T4 was significantly reduced among cases when compared to controls (p < 0.001). The mean levels of TSH were significantly higher among cases as compared to controls (p < 0.001). The mean concentration of ferritin was significantly lower among cases as compared to controls (p < 0.001).  

Table 1. Mean concentrations of serum free T3, freeT4, TSH and ferritin in study subjects

           Cases (n=55); Controls (n=55)

Hypothyroidism is an endocrine disorder with multiple etiologies and clinical features; therefore, diagnosis and treatment are influenced by coexisting medical conditions (18). Trace elements like iodine, iron, selenium and zinc are required for proper thyroid functions (9) and the coexisting deficiencies of these elements can impair the functions of the thyroid gland (19). The present study revealed that the mean serum ferritin levels were significantly lower in subjects with hypothyroidism as compared to euthyroid subjects. The results indicate a significant association of serum ferritin with hypothyroidism. This is in total agreement with many earlier studies. In the recent past, a study reported a significant correlation of T4 and TSH with serum ferritin levels (20). Many studies demonstrated that the subjects with hypothyroidism had significantly lower serum ferritin concentration than the euthyroid subjects (21,22,29). Krishnamurthy et al. found that thyroid hormones such as T4, TSH, and rT3 were significantly associated with varying levels of serum ferritin (23). Saini et al. observed that subjects with hypothyroidism had higher levels of TSH, and lower levels of serum ferritin compared to the control group (24). Ferritin is a central protein that plays a pivotal role in iron metabolism. It is regulated post-transcriptionally by cellular iron status via iron-responsive elements in its messenger RNA (17).  It is an acute phase protein, and its serum levels are increased in inflammatory conditions or infections. However, under normal conditions, serum ferritin levels can be used as an indicator of tissue iron status (25). Serum ferritin has a protective antioxidant role by sequestering the iron (21). Iron is sequestered in the mineral core of ferritin in a ferric state (F3+). This safe keeping of iron in this unreactive form within ferritin reduces the concentration of reactive intracellular iron in a ferrous state (F2+) and lowers the potential for generation of oxidant species (26). Low serum ferritin levels accompany the release of free iron, which may contribute to increasing oxidative stress and damaging thyroid follicular cells, causing a reduction of thyroid hormone synthesis (22).

The metabolism of iron is intricate and closely connected with thyroid hormone metabolism as iron is one of the essential nutrients required for proper thyroid functions. Low serum ferritin levels can affect the thyroid gland and iron deficiency, as reflected in low serum ferritin levels, can cause an adverse effect on the thyroid gland which results in the genesis of thyroid dysfunction (27). Iron deficiency is the most prevalent nutritional deficiency in the world. Iron deficiency with or without anemia disrupts the metabolism of thyroid hormones. Iron deficiency impairs the activity of iron-dependent intracellular enzymes and thus thyroid hormone synthesis. For instance, it impairs thyroid hormone synthesis by reducing the activity of heme-dependent thyroperoxidase (19). It is crucial for the synthesis of thyroid hormones. It catalyzes the initial steps of thyroid hormone synthesis – iodine incorporation and coupling of MIT and DIT (11). Iron deficiency is one of the factors that initiates the inflammatory process in the thyroid gland, leading to the production of anti-thyroid antibodies like anti - TPO and anti-Tg. In iron-deficiency anemia, iodine supplementation is blunted. However, iron supplementation improves the efficacy of iodine supplementation (19). Iron deficiency can affect the peripheral conversion of the inactive thyroid hormone T4 to the active thyroid hormone T3 by affecting 5´ - deiodinase (23, 27). This conversion is important as the thyroid gland predominantly produces the prohormone T4 along with a small amount of the biologically active hormone T3. Most T3 is formed by enzymatic outer ring deiodination of T4 in the liver. Iron deficiency also causes slower turnover of T3 and impairment of binding of T3 to its nuclear receptor, thereby lowering utilization of thyroid hormones (19). The prevalence of subclinical hypothyroidism and overt hypothyroidism are more common among individuals with iron deficiency compared to individuals with mild or no iron deficiency (28).  Low serum ferritin levels and iron deficiency significantly correlate with subclinical hypothyroidism and overt hypothyroidism (29, 30), suggesting the potential clinical application of serum ferritin in hypothyroidism.

Limitation

The present study was a hospital-based case-control study design with a small sample size. Prospective studies with a larger sample size that include a complete iron profile and thyroid antibodies will shed more light on the status of serum ferritin with hypothyroidism.

The present study found that the serum ferritin levels were substantially lower in hypothyroid subjects, indicating a significant association of serum ferritin with hypothyroidism. Ferritin might be playing a role in protecting the thyroid gland from oxidative stress and iron plays a crucial role in thyroid hormone metabolism. Ferritin stores iron in tissues and its serum levels reflect tissue iron status. As serum ferritin levels deplete well before iron levels deplete in iron deficiency, estimation of serum ferritin levels could be useful in the evaluation and management of hypothyroidism.

1. Wilson SA, Stem LA, Bruehlman RD. Hypothyroidism: diagnosis and treatment. Am Fam Physician. 2021; 103(10): 605-613.
2. Persani L. Clinical review: central hypothyroidism: pathogenic, diagnostic, and therapeutic challenges. J Clin Endocrinol Metab. 2012; 97: 3068-78.
3. Alam M A, Quamri MA, Sofi G, Ansari S. Update of hypothyroidism and its management in Unani medicine. J Basic Clin Physiol Pharmacol. 2020; 32: 1-10.
4. Brito JP, Ross JS, El Kawkgi OM, Maraka S, Deng Y, Shah, et al. Levothyroxine use in the United States, 2008-2018. JAMA Intern Med. 202; 181(10): 1402-1405.
5. Gierach M, Rudewicz M, Junik R. Iron and ferritin deficiency in women with hypothyroidism and chronic lymphocytic thyroiditis - systematic review. Endokrynol Pol. 2024;75(3): 253-261.
6. Vanderpump M P. The epidemiology of thyroid disease. Br Med Bulletin. 2011; 99(1): 39-51.
7. Mc Aninch EA, Bianco AC. The history and future of treatment of hypothyroidism. Ann Intern Med. 2016; 164(1): 50-56.
8. Watt T, Cramon P, Hegedüs L, Bjorner JB, Bonnema SJ, et al. The thyroid-related quality of life measure ThyPRO has good responsiveness and ability to detect relevant treatment effects. J Clin Endocrinol Metab. 2014; 99(10), 3708-3717.
9. Zhou Q, Xue S, Zhang L, Chen G. Trace elements and the thyroid. Front Endocrinol (Lausanne). 2022; 13: 904889.
10. Leung A, Pearce EN, Braverman LE. Role of iodine in thyroid physiology. Expert Rev Endocrinol Metab. 2010; 5(4): 593-602.
11. Köhrle, J. Selenium, iodine and iron–essential trace elements for thyroid hormone synthesis and metabolism. Int J Mol Sci. 2023; 24: 3393.
12. Wang F, Li C, Li S, Cui L, Zhao J, Liao L. Selenium and thyroid diseases. Front Endocrinol (Lausanne). 2023; 14:1133000.
13. Severo JS, Morais JBS, de Freitas TEC, Andrade ALP, Feitosa MM, et al. The role of Zinc in thyroid hormones metabolism. Int J Vitam Nutr Res. 2019; 89(1-2): 80-88.
14. Wang W, Knovich MA, Coffman LG, Torti FM, Torti SV. Serum ferritin: Paste, present and future. Biochim Biophys Acta. 2010;1800(8): 760-9.
15. Knovich MA, Storey JA, Coffman LG, Torti SV, Torti FM. Ferritin for the clinician. Blood Rev. 2009; 23(3): 95-104.
16. Noemia LM, Carmen VL (2018) Ferritin: Could be a health indicator. J Fam Med Dis Prev. 2018; 4 (2): 1-8.
17. Daru J, Colman K, Stanworth SJ, De La Salle B, Wood EM, et al. Serum ferritin as an indicator of iron status: what do we need to know? Am J Clin Nutr. 2017; 106(6):1634S-1639.
18. Garber JR, Cobin RH, Gharib H, Hennessey JV, Klein I, et al. American Association of Clinical Endocrinologists and American Thyroid Association Taskforce on Hypothyroidism in Adults. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Endocr Pract. 2012 ;18(6):988-1028.
19. Zimmermann MB, Köhrle J. The impact of iron and selenium deficiencies on iodine and thyroid metabolism: biochemistry and relevance to public health. Thyroid. 2002 O;12(10): 867-78.
20. Eftekhari MH, Keshavarz SA, Jalali M, Elguero E, Eshraghian MR, Simondon KB. The relationship between iron status and thyroid hormone concentration in iron-deficient adolescent Iranian girls. Asia Pac J Clin Nutr. 2006;15(1):50-5.
21. Sumitha Prabhu PS, Cheriyan S, Sulaiman L, A comparative study of serum ferritin and thyroid stimulating hormone (TSH) levels in hypothyroid and euthyroid subjects. Int J Clin Biochem Res. 2022; 9(3): 250-253
22. Haroon Rashid, Naresh Kumar Suman, Sude Kumar Singh. A study on serum ferritin and hypothyroidism among patients attending a tertiary care hospital with special emphasis on effect of thyroid hormone replacement therapy. IJHCR. 2022; 5(3): 749–751.
23. Krishnamurthy HK, Reddy S, Jayaraman V, Krishna, K, Song, Q, et al. Association of serum ferritin levels and thyroid hormones. Open J Clin Diagn. 2023; 13: 68-79.
24. Saini V, Chopra S, Kaur J, Kaur M. Evaluation of serum ferritin Levels in patients of hypothyroidism. Indian J Med Biochem. 2024;28(3):60–62.
25. Fonseca Ó, Ramos AS, Gomes LTS, Gomes MS, Moreira AC. New perspectives on circulating ferritin: Its role in health and disease. Molecules. 2023; 28: 7707.
26. Dignass A, Farrag K, Stein J. Limitations of serum ferritin in diagnosing iron deficiency in inflammatory conditions. Int J Chronic Dis. 2018; 2018: 1-11.
27. Garofalo V, Condorelli RA, Cannarella R, Aversa A, Calogero AE, La Vignera S. Relationship between iron deficiency and thyroid function: A systematic review and meta-analysis. Nutrients. 2023;15(22): 4790.
28. Szklarz M, Gontarz-Nowak K, Matuszewski W, Bandurska-Stankiewicz E. Iron: Not just a passive bystander in AITD. Nutrients. 2022;14(21): 4682.
29. Lejla Čano Dedić, Emsel Papić, Arzija Pašalić, Dalila Smajlović, Sabina Šečić – Selimović, Sabina Šegalo. Correlation of serum ferritin and thyroid hormone levels. J Health Sci. 2023;13(3) S1:213-216.
30. Sylus AM, Priyatharshini M, Muraliswaran P, Lavanya M. Correlation of iron deficiency status with thyroid profile among subclinical and overt hypothyroidism patients attending a tertiary care hospital in Puducherry, India: A cross‑sectional study. Acta Med Int. 2024; 11:197-202.