Lipid Profile of Patients with Thyroid Dysfunction in Ayurveda Hospital

Background : Thyroid hormones play an indispensable role in various metabolic processes in the human body. Thyroid disorders other than iodine deficiency disorders in the form of thyroiditis, hypothyroidism or autoimmune thyroid dysfunctions are on rise. Objective : This study was done to study the prevalence and pattern of dyslipidemia in patients with thyroid dysfunction. Methods : It is a retrospective study based on the available biochemical data of 50 thyroid patients (33 females and 17 males) with age range of 26-68 years. Serum total cholesterol (TC), triglycerides (TG), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), very low density lipoprotein cholesterol (VLDL-C) triiodothyronine (T 3 ), thyroxine (T 4 ) and thyroid stimulating hormone (TSH), were measured using standard assays procedures. Results: The results showed that 82% of the study population has hypothyroidism with the higher prevalence among females. The mean values of T 3 , T 4 and TSH in patients with thyroid dysfunction were 0.8 0.05 ng/ml, 4.2 0.5 mg/dl and 9.45 1.2 mIU/ml, respectively. The mean values of TC, TG, HDL-C, LDL-C, and VLDL-C were 222.4 3.8 mg/dl, 180.3 8.2 mg/dl, 35.6 1.3 mg/dl, 151.6 6.2 mg/dl and 36.5 2.6 mg/dl respectively in patients with hypothyroidism. Hypothyroidism shows significant positive correlation with TC, TG and LDL. Results show that even a slight increase in serum TSH showed significant dyslipidemia. Conclusion : This study suggests that regular monitoring of lipid level in patients with thyroid dysfunction would be helpful in preventing cardiovascular diseases.


Estimation of total cholesterol
Cholesterol esters will be hydrolyzed by cholesterol esterase.Cholesterol will be oxidized into cholest-4-en-3-on and hydrogen peroxide by bacterial cholesterol oxidase.Hydrogen peroxide in the presence of phenol and amino-4-antipyrine forms a complex of red color showing absorption maximum at 500 nm by using a semi-automated enzymatic analyzer (Robonik, Mumbai, India).

Estimation of triglyceride
It is based on the principle that triglycerides in the serum sample are hydrolyzed enzymatically by the action of lipase to glycerol and fatty acids.The glycerol formed is converted to glycerol phosphate by glycerol kinase (GK).Glycerol phosphate is then oxidized to dihydroxyacetone phosphate by glycerol phosphate oxidase (GPO).The librated hydrogen peroxide is detected by a chromogenic acceptor, chlorophenol-4-aminoantipyrine, in the presence of peroxidase (POD).The red quinone formed is proportional to the amount of triglycerides present in the sample and is measured at 546 nm.

Estimation of total HDL-cholesterol
It is measured by using phosphotungstate precipitation method based on the principle that chylomicrons, VLDL and LDL fractions in serum or plasma are separated from HDL by precipitating with phosphotungstic acid and magnesium chloride.After centrifugation the cholesterol in the HDL fraction which remains in the supernatant is assayed with enzymatic cholesterol method using cholesterol esterase, cholesterol oxidase, peroxidase and the chromogen 4-aminoantipyrine.

Estimation of total LDL-cholesterol
The LDL-Cholesterol test is a two reagent homogenous system.The assay is comprised of two distinct phases.In phase one a unique detergent solubilizes cholesterol from non-LDL-lipoprotein particles.This cholesterol is consumed by cholesterol esterase, cholesterol oxidase, peroxidase and 4aminoantipyrine to generate a colorless end product.In phase two a second detergent in reagent 2 releases cholesterol from the LDLlipoproteins.This cholesterol reacts with cholesterol esterase, cholesterol oxidase and a chromogen system to yield a blue color complex which can be measured bichromatically at 540/660nm.The resulting increase in absorbance is directly proportional to the LDL-C concentration in the sample.

Estimation of total VLDL-cholesterol
The value of VLDL-cholesterol was calculated as one-fifth of the concentration of triglycerides.

Statistical analysis
The data obtained was analyzed for significance between the groups by one-way analysis of variance (ANOVA).Correlation studies (Pearson's correlation coefficients and significance) were performed between the variables of thyroid assay and serum lipid profile by using statistical software programme "SPSS evaluation version 22".

Results
Results of the present retrospective study showed that among 50 patients with thyroid dysfunction included in this study, female and male were 33 and 17, respectively (Table 1).The age range of female and male subjects was 26-65 years and 32-68 years, respectively.Results of the thyroid assay showed that, all individuals selected for the study were with thyroid dysfunction.The normal reference range considered for each parameter was already established reference value of our laboratory.The range of T3, T4 and TSH in patients with thyroid dysfunction were 0.2 -1.5 ng/ml, 2.4 -8.9 g/dl and 2.6 -19.5 mIU/ml, respectively (Table 2).The mean values of T3, T4 and TSH in patients with thyroid dysfunction were 0.8 ± 0.05 ng/ml, 4.2 ± 0.5 g/dl and 9.45 ± 1.2 mIU/ml, respectively.Results showed that female had higher prevalence of thyroid dysfunctions.Results of serum lipid profile showed that the mean values for TC, TG, HDL-C, LDL-C and VLDL-C were 222.4 ± 3.8 mg/dl, 180.3 ± 8.2 mg/dl, 35.6 ± 1.3 mg/dl, 151.6 ± 6..2 mg/dl and 36.5 ± 2.6 mg/dl, respectively (Table 3).Among all thyroid patients, hypothyroidism was found in 82%, while hypercholesterolemia was found in 92% of the individuals (Table 4).Similarly, hypertriglyceridemia and reduced HDL-Cholesterol was found in 76% and 42% respectively, while elevated LDL-C was found in 78 % of the individuals suffering from thyroid dysfunction.Result of the correlation studies demonstrated a negative correlation of TSH with T3 and T4, while a significant positive correlation of TSH was observed TC, TG and LDL.

Discussion
Thyroid disorders are very common with variable prevalence among the different populations.Recent decades have seen a growing understanding of the pleiotropic effects of thyroid hormones on various vascular and metabolic processes.Furthermore, insights are being developed into the complex interactions, at the phenotypic and molecular levels, between thyroid dysfunction and cardiovascular risk.Thus, our understanding has shifted from IJBR (2014) 05 (04) www.ssjournals.comthe simplistic concept of thyroid dysfunction as a benign disorder of hormone secretion to a more complete appreciation of its multiple deleterious effects on cardiovascular and metabolic function. 8,9,10Subclinical hypothyroidism is defined as an elevated TSH concentration in the presence of normal thyroid hormones. 11With the advent of sensitive assays for TSH measurements subclinical hypothyroidism will increasingly be diagnosed in healthy individuals with no overt features of thyroid disease.The clinical features of thyroid disorders tend to be nonspecific and fewer in elderly compared to younger patients and the symptoms are often confused with normal ageing process and coexisting diseases which may result in greater number of elderly patients being undiagnosed. 12esults showed higher prevalence of thyroid dysfunction in females which is in accordance with the earlier studies. 2,13,14It may be due to a sex difference in the prevalence of autoimmune diseases.Results suggested that maximum number of patients with thyroid dysfunction had one or more types of dyslipidemia.Our results reveal high prevalence of hypercholesterolemia, hypertriglyceridemia high LDL-C levels and reduced HDL level, which are well known risk factors for cardiovascular diseases among patients.These patients are on high-risk without complications but already had significant dyslipidemia, which enhances the risk of cardiovascular events, certainly required therapeutic intervention.
There was a significant association between hypothyroidism and dyslipidemia which is in accordance with the result of Regmi et al and Cabral et al. 2,15 Increase of total cholesterol and LDL can be attributed to the effect of thyroid hormone on expression of LDL receptors and CYP7A, a rate limiting enzyme in bile acid synthesis.Decreased thyroid function not only increases the number of LDL particles but also promote LDL oxidation, thereby increasing the risk of atherosclerosis. 16HDL was increased in both overt and subclinical hypothyroidism, however, the increase was significant only in case of subclinical hypothyroidism.A study by Packard et al., reported that reduced HDL-C as a powerful predicator for premature coronary heart diseases. 17levation in HDL cholesterol could be due to decreased activity of cholesteryl ester transfer protein and hepatic lipase.In addition, HDL-C is a ready substrate for hepatic lipase which converts it into smaller particles, which are readily cleared from the plasma.TG level is also increased in both overt and subclinical hypothyroidism which is attributable to the decreased activity of lipoprotein lipase that is responsible for the clearance of triglyceride rich lipoprotein.In subclinical hyperthyroidism, however, TC and LDL levels were slightly increased but not significant statistically.Despite the increased activity of HMG-CoA reductase, the cholesterol levels tend to be increased in hyperthyroidism due to augmented excretion of cholesterol by bile together with enhanced receptor mediated catabolism of LDL particles.Variations, generally, not very marked, observed in TG levels could be due to the action of thyroid hormone on VLDL. 17,18yslipidemia management in people with thyroid dysfunction starts with a thorough evaluation that aims to identify secondary causes that might contribute to the abnormal lipid profile.Medication alongwith dietary modifications are the cornerstones of management.Our study clearly shows that lipid fractions are abnormal in thyroid disorders.Realizing the fact that individuals with thyroid dysfunction have a high probability of developing cardiovascular and cerebrovascular disease, it is essential that an individual who has thyroid should take care of his dyslipidemia. 19,20Prospective and longitudinal studies are needed at the time of diagnose to estimate true population prevalence of dyslipidemia in patients with thyroid dysfunction.Therefore, this study indicates that monitoring of lipid level in patients with thyroid dysfunction would be helpful in preventing cardiovascular diseases.As this is a retrospective study based on the available clinical records, the information related to the diabetes status and medication of the individuals was not available.Earlier studies have already established a clear association between thyroid disorders, diabetes mellitus and dyslipidemia. 21,22,23Unrecognized dyslipidemia in thyroid dysfunction will amplify cardiovascular risk.The increased frequency of dyslipidemia in thyroid dysfunction calls for a systematic approach to lipid profiling.

Conclusion
In the present study, we observed higher TSH levels or hypothyroidism in subjects with thyroid dysfunction.Therefore, selective regular screening strategy may be initiated to monitor the serum lipid profile of those patients who are at the greatest risk of thyroid dysfunction, such as those with diabetes mellitus, baseline positive antibodies or TSH concentrations in the upper half of the normal reference range.This is a preliminary study with a small sample size, hence, larger epidemiological studies is required to find out the actual prevalence and incidence of dyslipidemia in thyroid abnormality.

Table 2 : The concentration of T 3 , T 4 and TSH in patients with thyroid dysfunction T3 1 T4 2 TSH 3 Normal Range Calculated Range Mean Normal Range Calculated Range Mean Normal Range Calculated Range
1Units expressed as ng/ml.; 2 Units expressed as g/dl.; 3 Units expressed as mIU/ml *Statistically significant (P<0.05) as compared to normal range for respective thyroid level.