From the Guidelines
Thyroid dysfunction can significantly impact cholesterol levels, with hypothyroidism often causing elevated total cholesterol, LDL, and triglycerides, while hyperthyroidism can lower cholesterol levels. The relationship between thyroid function and cholesterol levels is complex, and treatment of hypothyroidism with thyroid hormone replacement medication like levothyroxine can improve cholesterol profiles within 3-6 months of achieving normal thyroid function 1.
Key Points to Consider
- Hypothyroidism can lead to decreased metabolism of lipids and reduced activity of LDL receptors in the liver, resulting in elevated cholesterol levels 1.
- Treatment of subclinical hypothyroidism has shown mixed results in terms of its effect on lipid levels, with some trials suggesting potential beneficial effects, but the results are inconsistent and of uncertain clinical importance 1.
- Even mild or subclinical hypothyroidism can affect cholesterol levels, making proper thyroid management an essential component of cardiovascular health for affected individuals.
- Thyroid testing, including measuring TSH and possibly T4 levels, is important to determine if thyroid dysfunction is contributing to lipid abnormalities.
Clinical Implications
- Patients with high cholesterol should undergo thyroid testing to determine if thyroid dysfunction is contributing to lipid abnormalities.
- Treatment of hypothyroidism with thyroid hormone replacement medication should be considered to improve cholesterol profiles and overall cardiovascular health.
- The most effective approach to managing cholesterol levels in patients with thyroid dysfunction is to achieve normal thyroid function through treatment, rather than relying solely on lipid-lowering medications.
From the Research
Thyroid Dysfunction and Cholesterol Levels
- Thyroid dysfunction, including hypothyroidism, can negatively affect lipid metabolism, leading to hypercholesterolemia and an increased risk of cardiovascular disease 2, 3, 4, 5.
- Hypercholesterolemia in hypothyroidism is mainly due to a reduction in low-density lipoprotein (LDL) receptor activity and diminished control by triiodothyronine (T3) of sterol regulatory element-binding protein 2 (SREBP-2) 2.
- Thyroid hormone administration can therapeutically reverse the dyslipidemic profile commonly occurring in hypothyroidism, and may also enhance the efficacy of hypolipidemic drugs such as statins 2, 5.
Effects of Thyroid Dysfunction on Lipid Profiles
- Overt hypothyroidism is characterized by hypercholesterolaemia, increased low-density lipoproteins (LDL), and apolipoprotein B (apo B) 4.
- High-density lipoprotein (HDL) levels are normal or elevated in severe hypothyroidism due to decreased activity of cholesteryl-ester transfer protein (CETP) and hepatic lipase (HL) 4.
- Hyperthyroidism exhibits an enhanced excretion of cholesterol and an increased turnover of LDL, resulting in decreased total and LDL cholesterol 4.
Treatment of Thyroid Dysfunction and Lipid Profiles
- Levothyroxine therapy in overt hypothyroidism leads to a significant decrease in total cholesterol, LDL-C, and triglycerides, and an improvement in the lipid profile 5.
- Treatment of overt hyperthyroidism is associated with worsening of the lipid profile, while subclinical hyperthyroidism does not change lipid parameters significantly 5.
- Statin use is associated with benefits of thyroid function, and total cholesterol changes serve as a mediator of the association between statin use and thyroid-stimulating hormone (TSH) levels 6.