| BackgroundHypothyroidism is the major cause of secondary dyslipidemia, the cause of which resides in a decreased cholesterol excretion and a marked increase in Apo B lipoproteins because of a decreased catabolism and turnover by reduced number of LDL receptors on the liver cell surface. In patients with Hypothyroidism, the decrease in catabolism is more important factor than decrease in synthesis of cholesterol. These lipid abnormalities are associated with endothelium dysfunction, diastolic hypertension and cardiovascular disease and can be treated with Levothyroxine replacement therapy. Although dyslipidemia and high risk atherosclerosis and cardiovascular diseases have been reported in some clinical studies, others have failed to demonstrate those findings in mild thyroid failure. There have been many controversies regarding treatment in subclinical hypothyroidism with Levothyroxine.ObjectiveTo study the changes in blood lipid profile in patients with hypothyroidism and to evaluate the effect of L-T4 replacement therapy on these blood lipid parameters. Method The study was done from September 2009 to January 2011 at China Japan Union hospital (Third Clinical Hospital) of Jilin University. The total of 70 Overt hypothyroid and 20 Subclinical hypothyroid patients from OPD and IPD were selected as cases.60 healthy individuals were selected as control group. OH was diagnosed on the basis of elevated TSH and low FT4 and FT3 levels. SH was diagnosed on the basis of elevated TSH>5mU/L with normal FT4 and FT3 levels. Persons with severe obesity (Body mass index, BMI>35 kg/m2) patients receiving drugs that interfere with the lipid metabolism, patients with familial secondary dyslipidemia, diabetes mellitus, and renal, hepatic or other systemic and inflammatory diseases were excluded from the study. The lipid parameters (TC, LDL-C, TG, Non HDL-C, HDL-C, Apo Al and Apo B) of the cases were measured and compared with that of the control group. Al1 the patients were treated with Levothyroxine therapy, the dose depending on the severity of the disease. The blood lipid parameters before and 3 months after treatment were compared in overt and subclinical hypothyroidism for the evaluation of efficacy of Levothyroxine therapy. Statistical analysis was done with paired t test, Pearson's correlation and ANOVAs using SPSS window (version 17.0, SPPS). P<0.05 was considered to be statistically significant.Results1. TC, LDL-C, TG, Non HDL-C, Apo B were significantly increased (P value<0.05) in patients with OH whereas Apo Al and HDL-C levels were not changed significantly in these patients as compared with control. In patients with SH, TC, LDL-C, Non HDL-C and Apo B were significantly increased (P value<0.05) whereas TG, HDL-C and Apo Al were not significantly changed as compared with control.2. In OH patients, as compared with SH, TC, LDL-C, Non HDL-C and Apo B were significantly increased (p value<0.05) where as TG, Apo Al and HDL-C were not changed significantly.3. In OH, all the blood lipid parameters, except Apo Al and HDL-C were significantly decreased with Levothyroxine treatment (P value<0.05).In SH, TC, LDL-C, Non HDL-C, and Apo B were decreased significantly (P value<0.05) after Levothyroxine treatment, whereas TG, HDL-C and Apo Al were not changed significantly.4. In OH, TSH was significantly negatively correlated with FT4 with the correlation coefficient-0.79. It was significantly positively correlated with TC, LDL-C, Non HDL-C, TG and Apo B with the correlation coefficient 0.78,0.67,0.72,0.59, and 0.63 respectively. However it was weakly positively correlated with HDL-C and ApoAl. In SH, TSH was significantly negatively correlated with FT4 with the correlation coefficient-0.90. It was significantly positively correlated with TC, LDL-C, Non HDL-C, and Apo B with the correlation coefficient 0.81,0.67,0.68, and 0.57 respectively, whereas weakly positively correlated with ApoAl, HDL-C and TG.Discussion1. In this study, as in other literature reports, OH patients were associated with significant increase in all the lipid parameters (TC, LDL-C, TG, Non HDL-C and Apo B) except Apo Al and HDL-C. Studies done before had controversies regarding change in HDL-C in OH patients. In this study it was not changed significantly.2. In this study, SH were associated with significant increase in TC, LDL-C, Non HDL-C and Apo B, but there were no significant changes in TG, HDL-C and Apo Al. Although dyslipidemia, high risk atherosclerosis and cardiovascular diseases have been reported in some clinical studies, others have failed to demonstrate those findings in mild thyroid failure. However, in SH patients with>10mU/L, many studies has shown dyslipidemia. But still there are many controversies regarding which parameters are significantly increased. In this study all the enrolled patients had TSH>10mU/L.3. In OH patients, as compared with SH patients, TC, LDL-C, Non HDL-C and Apo B were significantly increased (p value<0.05) where as TG, Apo Al, and HDL-C were not changed significantly.4. Like in many previous studies, this study also showed patients of OH had significant improvement in all blood lipid parameters with L-T4 replacement therapy, whereas no significant changes HDL-C and Apo Al.5. In this study, SH patients had significant improvement in TC, LDL-C, Non HDL-C and Apo B with L-T4 therapy whereas no significant changes in TG, HDL-C and Apo Al. Although there have been many controversies regarding treatment in subclinical hypothyroidism with Levothyroxine, this study showed significant improvement with LT-4 in most of the lipid parameters that are risk for cardiovascular disease. It could be because all the SH patients in this study had TSH>10mU/L before the treatment was started.6. In both the cases, TSH had significant negative correlation with FT4 but significant positive correlation with TC, LDL-C, Non HDL-C and Apo B whereas weak correlation with Apo Al and HDL-C. TSH had significant positive correlation with TG in OH, whereas it had weak positive correlation in SH.Conclusion1. Overt hypothyroidism and Subclinical hypothyroidism were both associated with dyslipidemia. However, the increment in lipid parameters was more in OH patients than SH.2. Dyslipidemia was improved after L-T4 replacement therapy in both OH and SH patients.3. In both the cases, TSH was significantly negatively correlated with FT4 and significantly positively correlated with TC, LDL-C, Non HDL-C and Apo B.
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