Endocrine Abstracts

Background: We have previously shown that a higher BMI and less favorable body composition are associated with relatively higher FT₃ levels (within the euthyroid range) in healthy young men. In this study, we aimed to investigate whether FT₃ and the ratio FT₃:FT₄ are also associated with cardiovascular markers in a healthy euthyroid population of middle-aged men and women.

Methods: Thyroid parameters were measured in 2524 subjects from the Asklepios Study (35–55 years). Analyses were restricted to 2315 subjects (1138 women and 1177 men), not using thyroid medication nor having anti-TPO levels above clinical cut-off or TSH levels outside the reference range (0.27–4.2 mU/l). Thyroid function parameters were determined by automated electrochemiluminescence. Statistical analysis was performed by linear and logistic regression analysis in SPSS.

Results: (F)T₃ and the ratio FT₃:FT₄ were significantly positively related to BMI and waist circumference (both P<0.0001) and other elements of the metabolic syndrome, i.e. triglycerides, systolic and diastolic blood pressure and fasting plasma glucose (all P values <0.001). (F)T₃ and the ratio FT₃:FT₄ were also associated with lower HDL-levels (P<0.001). The presence of the metabolic syndrome as a whole (both according to the IDF as the ATPIII-criteria) was also related to higher (F)T₃ levels and a higher FT₃:FT₄ ratio (OR=2, P<0.0001). All the associations regarding the metabolic syndrome remained significant after adjustment for sex, age, height, weight or waist circumference, and smoking. The FT₃:FT₄ ratio was further positively associated with obesity-related predictors of cardiovascular events: elevated IL6 (>1.5 pg/ml; OR=1.5, P=0.001) and elevated hs-CRP (>3 mg/l; OR=1.7, P=0.001), even after adjustment for sex, age, height, weight or waist circumference, and smoking.

Conclusion: In healthy euthyroid middle-aged men and women, higher (F)T₃ levels and a higher FT₃:FT₄ ratio are associated with a cluster of obesity-related cardiovascular risk markers. However, no causal inferences can be made from this cross-sectional study.