Association between FT3 Levels and Exercise-Induced Cardiac Remodeling in Elite Athletes

Abstract

Background: Previous studies demonstrated that variations of fT3, even within the euthyroid range, can influence cardiac function. Our aim was to investigate whether thyroid hormones, even within the euthyroid range, are associated with the magnitude of exercise-induced cardiac remodeling in Olympic athletes.

Methods: We evaluated 1342 Olympic athletes (mean age 25.6 ± 5.1) practicing different sporting disciplines (power, skills, endurance, and mixed). Athletes underwent blood testing (thyroid stimulating hormone, fT3, and fT4), echocardiography, and exercise-stress testing. Athletes taking thyroid hormones, affected by thyroiditis, or presenting TSH out of ranges were excluded.

Results: The level of thyroid hormones varied according to the type of sporting discipline practiced: endurance athletes presented the lowest TSH (p < 0.0001), fT3 (p = 0.007), and fT4 (p < 0.0001) in comparison to the remaining ones. Resting heart rate (HR) was positively correlated to fT3 in athletes of different disciplines (power: p = 0.0002, R2 = 0.04; skill: p = 0.0009, R2 = 0.05; endurance: p = 0.007, R2 = 0.03; and mixed: p = 0.04, R2 = 0.01). The same results were seen for peak HR in the exercise-stress test in athletes engaged in power, skill, and endurance (respectively, p < 0.0001, R2 = 0.04; p = 0.01, R2 = 0.04; and p = 0.005, R2 = 0.02). Moreover, a positive correlation was observed with cardiac dimensions, i.e., interventricular septum (power: p < 0.0001, R2 = 0.11; skill: p = 0.02, R2 = 0.03; endurance: p = 0.002, R2 = 0.03; mixed: p < 0.0001, R2 = 0.04). Furthermore, fT3 was directly correlated with the left ventricle (LV) end-diastolic volume in skills (p = 0.04, R2 = 0.03), endurance (p = 0.04, R2 = 0.01), and mixed (p = 0.04, R2 = 0.01).

Conclusions: Thyroid hormones, even within the euthyroid range, are associated with cardiac adaptive response to exercise and may contribute to exercise-induced cardiac remodeling.

Keywords: athletes; heart; hormones; sport cardiology; thyroid.

Figure 1

Linear regression analysis between gender and heart rate at rest and at peak of exercise-stress test. (A) Rest heart rate in male athletes; (B) rest heart rate in female athletes; (C) peak heart rate in male athletes; (D) peak heart rate in female athletes. Abbreviations: HR: heart rate.

Figure 2

Linear regression analysis between serum fT3 values and interventricular septum thickness (Left Panel) and left ventricle end-diastolic volume indexed (Right Panel). Abbreviations: IVS: interventricular septum; LVEDVi: left ventricle end-diastolic volume indexed.

Figure 3

Variations in rest heart rate in different sporting disciplines according to fT3 quartiles. Abbreviations: HR: heart rate.

Figure 4

Variations in LV wall (interventricular septum) thickness in different sporting disciplines according to fT3 quartiles. Abbreviations: IVS: interventricular thickness.