Thyroid function and lipid profile in euthyroid adults: the TCLSIH cohort study.

Area of Science:

• Endocrinology
• Metabolic Disorders
• Lipid Metabolism

Background:

• Thyroid hormones (THs) play a crucial role in regulating lipid metabolism, influencing synthesis, mobilization, and degradation.
• Dyslipidemia, characterized by abnormal lipid levels, is a significant risk factor for cardiovascular diseases.
• Limited prospective data exist on the association between serum THs and incident dyslipidemia in euthyroid individuals.

Purpose of the Study:

• To investigate the association between serum thyroid hormone levels (free triiodothyronine [FT3], free thyroxine [FT4], and thyroid-stimulating hormone [TSH]) and the risk of developing dyslipidemia.
• To explore these associations within a general euthyroid population aged 18 and over.

Main Methods:

• A prospective cohort study with a median follow-up of 3.0 years (approximately 5 years total).
• Serum FT3, FT4, and TSH levels were measured using chemiluminescence immunoassay.
• Multivariable Cox proportional hazards regression models were employed to analyze the relationship between baseline thyroid hormone levels and incident dyslipidemia (elevated total cholesterol [TC], triglyceride [TG], low-density lipoprotein cholesterol [LDL-C], or reduced high-density lipoprotein cholesterol [HDL-C]).

Main Results:

• The incidence rates for elevated TC, TG, LDL-C, and reduced HDL-C were 29.3%, 20.7%, 24.8%, and 19.5%, respectively.
• Increased FT3 concentrations were significantly associated with a decreased incidence of elevated TC (HR: 0.87, 95% CI: 0.79-0.97) and LDL-C (HR: 0.897, 95% CI: 0.808-0.995).
• A weak positive association was observed between TSH and the incidence of reduced HDL-C (P=0.02), while FT4 showed no significant association with incident dyslipidemia.

Conclusions:

• Lower serum FT3 levels are associated with an increased risk of dyslipidemia, particularly elevated TC and LDL-C, in euthyroid adults.
• Elevated TSH levels demonstrated a weak positive association with the incidence of reduced HDL-C.
• These findings highlight the role of thyroid hormone levels, specifically FT3, in lipid profile regulation and underscore the need for further research in this area.