Background and purpose: Although the relation between thyroid disorders and heart diseases had been described since decades ago, the association of thyroid-stimulating hormone (TSH) and lipoproteins is not very well elucidated.
Hypothesis: to verify if there are associations with TSH levels, lipid and lipoprotein subfractions in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil).
Methods: We evaluated at the ELSA-Brasil baseline (2008-2010) 3,742 middle-aged participants (1,960 women and 1,782 women) without previous cardiovascular disease and people who were taking neither drugs that can interfere with thyroid function nor lipid-lowering agents. All of them had their levels of total-cholesterol and its sub-fractions (LDL, VLDL and HDL subclasses); triglycerides and triglyceride-rich lipoprotein cholesterol [TRL-C (VLDL1+2-C VLDL3-C + IDL-C)] determined by ultracentrifugation (Vertical Auto Profile, Atherotech). We also calculated T-Chol/HDL-C and triglycerides/HDL-C ratios. The application multinomial logistic regression model obtained odds ratios (OR) with its respective 95% confidence interval (95% CI). They are presented as adjusted for age, sex, educational level, hypertension, diabetes, and smoking. Lipids tertiles were evaluated as dependent variables, the quintiles of TSH were considered as an independent variable, using first quintiles of TSH as the reference.
Results: The main associations obtained were between the highest levels of TSH (5th quintile) with the highest levels (3rd tertiles) of VLDL-C, OR=1.55 (95%CI, 1.18-2.04); triglycerides, OR=1.71 (95%CI, 1.30-2.24); VLDL-3-C, OR=1.48 (95%CI, 1.13-1.94); TC/HDL-C ratio, OR=1.37 (95%CI; 1.04-1.81) and TG/HDL-C ratio, OR=1.71 (95%CI; 1.29-2.26). A positive association between the lowest levels of HDL3-C (1st tertile) and the highest of TSH was also verified with OR= 1.43 (95%CI, 1.10-1.87). In women, we found positive associations with the 5th TSH quintiles and the 3rd tertiles of VLDL-C, OR 1.68;(95%CI 1.18-2.41); non-HDL-C, OR,1.50; (95%CI,1.04-2.16); Triglyceride-rich Lipoprotein Cholesterol,OR 1.42 (95%CI 1.00-2.02); VLDL3-C (OR,1.68;95%CI 1.16-2.45), TC/HDL-C ratio (OR 1.86;95% CI 1.29-2.69) and TG/HDL-C-ratio (OR 1.62;95%CI 1.12-2.35). In men, we found associations between the 5th quintile of TSH and the 3rd tertiles of TG (OR 1.59; 95%CI 1.07-2.36) and TG/HDL-C-ratio (OR 1.71; 95%CI 1.15-2.55).
Conclusions: In this sample of middle-aged participants from ELSA-Brasil, an unfavorable lipid profile, which included triglyceride-rich lipoproteins and their remnants were mostly associated with high levels of TSH. In the other hand, we observed a risky association between the lowest levels of HDL3-C and the highest levels of TSH. The majority of our findings were mainly reproduced among women.