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Lipoprotein(a) and other lipoproteins in hypothyroid patients before and after thyroid replacement therapy
Insights
Hypothyroidism elevates lipoprotein(a) (Lp(a)) and other lipid levels, increasing coronary artery disease (CAD) risk. Thyroid hormone replacement therapy (L-T(4)) significantly reduces these markers, mitigating atherosclerosis risk.
Area of Science:
- Endocrinology
- Cardiovascular Medicine
- Lipidology
Background:
- Thyroid hormones play a crucial role in regulating lipid metabolism.
- Dysregulation of thyroid function, particularly hypothyroidism, is linked to adverse lipid profiles.
- The impact of hypothyroidism on lipoprotein(a) (Lp(a)) and its contribution to coronary artery disease (CAD) risk requires further elucidation.
Purpose of the Study:
- To investigate the influence of thyroid hormones on serum Lp(a) concentrations and other lipid parameters.
- To assess the potential impact of these lipid alterations on CAD risk in hypothyroid patients.
- To evaluate the effect of levothyroxine (L-T(4)) replacement therapy on Lp(a) and lipid levels.
Main Methods:
- A cross-sectional study comparing 36 hypothyroid patients with 165 age-matched euthyroid controls.
- Measurement of thyroid function tests, fasting serum lipids, and lipoproteins (including Lp(a)).
- A follow-up study involving L-T(4) therapy in hypothyroid patients to assess changes after thyroid state normalization.
Main Results:
- Hypothyroid patients exhibited significantly higher levels of Lp(a), total cholesterol (TC), LDL-C, apo A-I, apo B, and a higher TC/HDL-C ratio compared to controls.
- Serum thyroid-stimulating hormone levels positively correlated with Lp(a), LDL-C, and TC.
- L-T(4) therapy led to significant reductions in Lp(a) (32.3%), LDL-C (22.8%), TC (17%), apo A-I (9.6%), and apo B (9.3%), decreasing CAD risk (TC/HDL-C ratio by 19.9%).
Conclusions:
- Hypothyroidism is associated with elevated serum Lp(a) and LDL-C levels, contributing to increased CAD risk.
- Thyroid hormone-dependent mechanisms appear to modulate Lp(a) concentrations.
- L-T(4) therapy can effectively reduce Lp(a) and other atherogenic lipid parameters, potentially lowering the risk of premature atherosclerosis in hypothyroid individuals.
Aims:
To analyse the influence of thyroid hormones on serum lipoprotein(a) (Lp(a)) concentration and other lipid parameters, and hence potentially on coronary artery disease (CAD) risk.
Methods:
Thirty-six patients with hypothyroidism and 165 age-matched control euthyroid subjects were evaluated in a cross- sectional study, determining thyroid function tests and fasting serum lipids and lipoproteins. In a follow-up study for those hypothyroid patients the same determinations were repeated after normalization of thyroid state by levothyroxine (L-T(4)) replacement therapy. Patients needing other treatments were excluded. At baseline, patients with hypothyroidism had significantly higher levels of Lp(a), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), apolipoprotein (apo) A-I and apo B, and a higher TC/high-density lipoprotein cholesterol (HDL-C) ratio than control subjects.
Results:
Severity of the hypothyroid state, expressed by serum thyroid-stimulating hormone, was correlated with serum levels of Lp(a), LDL-C, and TC (r= 0.64, 0.52, 0.49, P= 0.005, P= 0.033, P= 0. 048, respectively). The pretreatment Lp(a) levels were also correlated with those of posttreatment Lp(a)(r= 0.68, P= 0.002). All patients, who presented basal Lp(a) levels higher than 30 mg/dl, showed a decrease in Lp(a) concentrations by L-T(4)therapy, and these normalized in eight cases (22.2%). Euthyroid state gave rise to a significant reduction of serum Lp(a) by 32.3%, of LDL-C by 22. 8%, of TC by 17%, of apo A-I by 9.6%, and of apo B by 9.3%. After L-T(4)therapy, CAD risk, expressed as TC/HDL-C ratio, decreased by 19.9%.
Conclusions:
These results show that hypothyroidism is associated not only with elevated serum levels of LDL-C but also with elevated serum Lp(a) concentrations. Lp(a) levels may be at least partially modulated by thyroid hormone-dependent mechanisms, thus increasing the risk of developing premature atherosclerosis in hypothyroid state, that might be reduced by L-T(4)therapy.