Thyroid Hormones within the Normal Range and Cardiac Function in the General Population: The EPIPorto Study

Area of Science:

• Endocrinology
• Cardiology
• Internal Medicine

Background:

• Thyroid dysfunction (hypo- and hyperthyroidism) significantly alters cardiac structure and function.
• The impact of thyroid hormone levels within the normal range on cardiac parameters in the general population remains unclear.

Purpose of the Study:

• To investigate the association between thyroid function tests (TSH, FT4, FT3) within the reference range and cardiac structure and function.
• To explore potential nonlinear relationships between thyroid hormones and cardiovascular parameters.

Main Methods:

• Cross-sectional analysis of 835 participants aged ≥45 years from the EPIPorto cohort.
• Exclusion of individuals with thyroid dysfunction or cardiovascular disease.
• Echocardiography for cardiac assessment; linear regression and restricted cubic splines for association analysis, adjusted for multiple confounders.

Main Results:

• Positive association between FT3 and heart rate; positive association between TSH and diastolic blood pressure.
• Inverse association between TSH and left ventricular (LV) volumes; nonlinear associations observed for LV wall thickness with FT4 and ejection fraction with FT3.
• No significant associations found for diastolic function parameters in adjusted models.

Conclusions:

• Thyroid function within the normal reference range is linked to heart rate, blood pressure, and cardiac structure.
• Higher thyroid function (lower TSH, higher FT4/FT3) correlates with increased heart rate, decreased diastolic blood pressure, and larger LV volumes.
• Left ventricular wall thickness and ejection fraction exhibit a U-shaped relationship with thyroid hormone levels.