Thyroid Hormone Levels, even within the Euthyroid Range, are Associated with Lipid Levels

Area of Science:

• Endocrinology
• Lipid Metabolism
• Thyroid Function

Background:

• Thyroid dysfunction is linked to dyslipidemia.
• The specific relationship between thyroid hormones and lipids in euthyroid individuals remains unclear.

Purpose of the Study:

• To investigate the association between thyroid profile parameters (free T3, free T4, TSH) and lipid profiles in euthyroid subjects.
• To explore potential differences in these associations based on sex and TSH levels.

Main Methods:

• Cross-sectional study involving 100 euthyroid patients.
• Measured thyroid parameters: free T3 (fT3), free T4 (fT4), and TSH.
• Assessed correlations between thyroid hormones and lipid components (total cholesterol, HDL, LDL).

Main Results:

• Free T3 (fT3) positively correlated with HDL cholesterol and negatively with total cholesterol.
• Free T4 (fT4) and the fT3/fT4 ratio showed a positive correlation with HDL cholesterol.
• These associations, especially with HDL, were more significant in men and in participants with TSH ≥ 3 µIU/mL.

Conclusions:

• Free T3 (fT3) demonstrates a consistent, beneficial association with lipid levels, notably HDL cholesterol, in euthyroid individuals.
• The positive impact of fT3 on HDL is more pronounced in men and those with TSH levels at or above 3 µIU/mL.