Introduction
Hypothyroidism is a clinical syndrome resulting from a deficiency of thyroid hormones, which in turn results in a generalized slowing down of metabolic process.1 Overt hypothyroidism (HO) defined as high TSH levels with low levels of FT4 and / or FT3.2 Hypothyroidism is a common condition that is related to premature atherosclerosis and its clinical consequences such as myocardial infarction.3 The increased cardiovascular morbidity in hypothyroid patients has been related to elevated levels of Total cholesterol and Low density lipoproteins cholesterol, which are normalized after thyroid hormones replacements.4 Total Homocysteine (tHcy) in plasma is an independent risk factor for cardiovascular disease.5, 6 Homocysteine (Hcy) is a sulfhydryl-containing amino acid is synthesised during the conversion of methionine to cysteine.2 Plasma Hcy levels is affected by several genetic, physiological and life style factors.7 Hyperhomocysteinemia induces endothelial injury, oxidative stress, smooth muscle hypertrophy and oxidation of LDL-Cholesterol and the process of atherosclerosis and cardiovascular diseases. Increased tHcy levels might be the result of two mechanisms either increased tHcy formation or decreased renal tHcy clearance due to direct effect of the thyroid hormones on the tHcy metabolism in the liver and clearance in the kidney. It may be explained as thyroid hormone deficiency decreases hepatic levels of enzymes involved in the remethylation pathway of tHcy to methionine, methylene tetrahydrofolate reductase (MTHFR) leading to hyperhomocystenemia.8 The kidney most likely plays an important role in Hcy clearance and metabolism, as it does with other amino acids. In hypothyroidism systemic vascular resistance is increased and leads to reduced renal blood flow and low GFR (Glomerular filtration Rate). Thus it reduces its clearance and cause hyperhomocysteinemia.9
Materials and Methods
Female patients of age group between 18-50 years clinically suspected and biochemically confirmed overt hypothyroid cases were selected from Medicine & Endocrinology OPDs and Inpatients wards at ESIC Model Hospital, Rajajinagar, Bengaluru. Age and gender matched blood donating volunteers in Blood Bank of ESIC Model Hospital, Rajajinagar, Bengaluru served as control group. A study was carried out for a period of 18 months from January 2018- June 2019.
Criteria for selection of hypothyroidism was based on laboratory biochemical investigations. TSH > 10 μIU /ml; decreased FT4 < 0.58 ng/dl. & normal or decreased FT3 ≤ 2.45 pg/ml.10, 11, 12 From correlational study of previous literature, r = 0.228 we achieved 80% power of the study and 5% level of significance and we arrived to a sample size of 100 (50 cases and 50 controls). After taking informed consent, under aseptic precautions, about 5ml of venous blood was drawn from the selected subjects after overnight fasting of 10-12 hours.
Exclusion criteria
Cardiac diseases like Ischemic Heart diseases.
Renal diseases like Chronic Renal Failure.
Chronic diseases like Hypertension, Stroke, DVT.
Metabolic disorders like Homocysteinurias.
Treatment with drugs like Phenobarbitone, Phenytoin, Methotrexate, Propylthiouracil.
Methimazole, lithium etc, were excluded from study
Methods
TSH, FT4, FT3 is estimated using Chemiluminescence Immunoassay in automated Beckman Coulter Access 2 analyzer.10, 11, 12 Normal range of TSH is 0.34-5.60 μ IU/ml, FT4 is 58-1 64 ng/dl & FT3 is 2 45-4 25 pg/ml,
Homocysteine is estimated using Homocysteine enzymatic assay methodology from Cobas Integra 400 plus.13 Normal range is 5-15 μmol/L.
Statistical analysis
All statistical analysis was performed using the prism pad software to indicate the significance between the mean values of hypothyroid patients and control group. Data were given as Mean ± SD, p < 0.05 were considered significant. Correlation was done using Pearson Correlation.
Results
In this study, the mean age in control group was found to be 27 ± 0.53 years and that of overt hypothyroid cases was 32.04 ± 0.82 years. As shown in Table 1, the mean TSH levels in control group was found to be 2.14 ± 0.39 µIU/ml and that of overt hypothyroid cases was 30.91 ± 10.21 µIU/ml (p <0.0001) {Figure 1}. As shown in Table 1, the mean FT4 in control group was found to be 0.89 ± 0.017 ng/dl and that of overt hypothyroid cases was 0.59 ± 0.23 ng/dl (p value <0.0001). As shown in Table 1, the mean FT3 in control group was found to be 3.16 ± 0.38 pg/ml and that of overt hypothyroid cases was 2.84 ± 0.39 pg/ml (p <0.0001). As shown in Table 2, the mean serum Homocysteine in control group was found to be 9.21 ± 2.27 μmol/L and that of overt hypothyroid cases was 19.24 ± 7.15 μmol/L (p <0.0001) {Figure 2}. As shown in Table 3, there is statistically significant strong positive correlation between Hcy and TSH levels as shown in Figure 3 and negative correlation between Hcy and FT4, FT3 levels as shown in Figure 4, Figure 5.
Table 1
Thyroid profile
| TFT HormonesMean ± SD | Controls | Cases | P value |
| TSH(μIU/ ml) | 2.146±0.3909 | 30.91±10.21 | <0.0001 |
| FT4(ng/dl) | 0.8988±0.01783 | 0.5992±0.2299 | <0.0001 |
| FT3 (pg/ml) | 3.164±0.3842 | 2.84±0.3914 | <0.0001 |
Discussion
In our study we found that serum Homocysteine is significantly increase in Overt Hypothyroid patients compared to Control groups 19.24 ±7.158μmol/L vs 9.214± 2.276μmol/L.
In our study there is statistically significant strong positive correlation between Hcy and TSH and negative correlation between Hcy and FT4, FT3.
Our study is in accordance with Molham Ali Al-Habori et al.,14 Aqsa Malik et al.,15 Saleh A Bamashmoos et al., 8 Yande Zhou et al.,2 Rafael Luboshitzy et al.,16 Xuejie Dong et al.,17 Manju Chandankhede et al.18 Our study is not in accordance with Anjali R. Metgudmath et al.19
High plasma homocysteine concentration induces pathologic changes in the arterial wall and thus is strongly associated with an increased risk of atherosclerosis, later manifested as cardiovascular, cerebrovascular and peripheral vascular events. There are consistent reports that patients with hypothyroidism have elevated total Homocysteine in plasma.20
In hyperhomocysteinemia, homocysteine stimulates protease endothelial cell activator of factor V and directly activates coagulation in the absence of thrombin.
Hyperhomocysteinemia favors binding of lipoprotein(a to fibrin thus reduces plasminogen activation and inhibits fibrinolysis
Homocysteine thiolactone causes LDL cholesterol to aggregate and then are phagocytosed by vascular macrophages to form foam cells. Homocysteine thiolactone released from foam cells produces free radicals and causes endothelial cell damage.9
Conclusion
In our study there is a significant increase in levels of Serum Homocysteine in cases as compared to controls (p = <0.0001). Also there is a positive correlation between Serum Homocysteine and TSH levels. Hence, increased Homocysteine levels may contribute to a greater cardiovascular risk in Overt Hypothyroidism.
We can conclude from our study that patients suffering from Overt Hypothyroidism may be investigated for Serum homocysteine levels, which can be used as a possible marker for screening atherosclerosis and necessary treatment can be initiated at the earliest to prevent the progression of cardiovascular changes in these patients.
