Effects of thyroid ft3 levels on exercise induced remodelling in elite athletes practicing different sporting disciplines

Introduction Free triiodothyronine (fT3) profoundly affects the cardiovascular system. Studies in the general population demonstrated that variations in thyroid hormone levels, even within the euthyroid range, can influence cardiac parameters. Purpose Aim was to investigate how thyroid hormone, within the limits of normality, affects exercise-induced cardiac remodelling in a large cohort of Olympic athletes. Methods We evaluated 1342 Olympic athletes (mean age 25.6±5.1) practising different sporting disciplines (power, skills, endurance and mixed). Athletes underwent blood (thyroid stimulating hormone, fT3 and fT4), echocardiographic and exercise-stress tests. Athletes assuming thyroid hormones, with thyroiditis or TSH out of the normal ranges were excluded. Results In all disciplines rest heart rate (HR) was positively correlated to fT3 (power: p=0.0002; R2=0.04,; skills: p=0.0009; R2=0.05; endurance: p=0.007; R2=0.03 and mixed: p=0.04; R2=0.01). Same for peak HR at exercise-stress test in power, skills 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 interventricular septum (power: p<0.0001; R2=0.11; skills: p=0.02; R2=0.03; endurance: p=0.002; R2=0.03; mixed: p<0.0001; R2=0.04). Furthermore, fT3 directly correlated with left ventricle 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). Conversely, thyroid hormones were influenced by type of sporting discipline practiced: endurance athletes presented the lowest TSH (p <0.0001), fT3 (p = 0.007) and fT4 (p < 0.0001). Conclusions Our study demonstrated a close, bidirectional relationship between exercise and thyroid function. Chronic aerobic exercise influence thyroid hormones by lowering TSH, fT3 and fT4 as an adaptive mechanism. However, on the other side small variation of fT3 circulating levels, even within the normal range, affect heart morpho-functional parameters (rest and peak heart rate, interventricular septum, left ventricle end-diastolic volume indexed) in all sporting disciplines and influence the athlete’s heart response to exercise induced adaptive mechanisms. Therefore, thyroid function assessment should be taken into account when an evaluation on athlete’s heart is performed. Influence of ft3 on heart rate. Influence of ft3 on IV septum.