Subclinical hypothyroidism (SCH) is a common condition affecting 3-10% of the general population, especially in women older than 50 years old. It is controversial whether SCH can lead to increased risks of cardiovascular (CV) disease and whether treatment with L-thyroxine reverses these risks. The present study was designed to evaluate the effect of L-thyroxine treatment in SCH on lipid profile, atherosclerosis, endothelial function, serum inflammatory factors and adipocytokines.

Inclusion Criteria:

• Male and female aged of 18 to 60 years old;
• Diagnosis was subclinical hypothyroidism(elevated serum thyroid-stimulating hormone levels with normal serum free T4 levels measured at least two times with a three-month interval);
• untreated.

Exclusion Criteria:

• Pregnancy or lactation women;
• Presence of pituitary/hypothalamic disorders, diabetes mellitus or other endocrinal and metabolic disorders;
• Presence of psychological or physical disabilities,acute infection, cerebrovascular or cardiovascular disease, chronic respiratory disease and other illnesses known to alter lipid metabolism;
• Taking lipid-lowering agents and other drugs that known to influence thyroid function, blood pressure, heart function or bile acids;
• Obviously poor compliance.