Levothyroxine Therapy and Predictors of Cardiovascular Risk in Clinical Hypothyroidism: A Prospective Cohort Study

Abstract

Background Hypothyroidism is associated with hypoadiponectinemia, insulin resistance, and increased cardiovascular risk. The association of adiponectin, insulin resistance, and future cardiovascular risk in clinical hypothyroidism and the effect of levothyroxine are non-conclusive because of the contradictory results. The present prospective cohort study has been conducted to evaluate the effect of levothyroxine on serum adiponectin, insulin resistance, and cardiovascular risk in patients with clinical hypothyroidism. Methods Sixty patients with clinical hypothyroidism who were prescribed levothyroxine were recruited following selection criteria and changes in Zulewski's score, glycemic parameters, homeostatic model assessment of insulin resistance (HOMA-IR), quantitative insulin sensitivity check index (QUICKI), lipid profile, serum adiponectin, serum high-sensitivity C-reactive protein(hs-CRP), cardiovascular risk indices, and Framingham risk score were assessed 12 weeks post-levothyroxine therapy. Receiver operating characteristic (ROC) analysis was done to detect the cut-off for adiponectin levels to differentiate between responders and non-responders. Neural network models were created to predict the risk of cardiovascular morbidity. Results Post-levothyroxine therapy, there was a significant improvement in body mass index(BMI) (p = 0.025), diastolic blood pressure (p = 0.021), Zulewski's score (p< 0.001), serum insulin (p = 0.005), fasting sugar (p < 0.001), serum adiponectin (p < 0.001), thyroid profile (p < 0.001), total cholesterol (p < 0.001), low-density lipoprotein (p < 0.001), high-density lipoprotein (p = 0.007), triglycerides (p = 0.002), and subcutaneous fat (p = 0.015). Serum adiponectin showed significant improvement in hypothyroid patients compared to euthyroid individuals (mean difference: -2.21; 95% CI: -2.52 to -1.91; p < 0.001). Mean difference in insulin resistance (HOMA-IR: 0.3, p < 0.001; QUICKI: -0.002, p < 0.001) and cardiovascular risk (atherogenic index: 0.12, p = 0.04; coronary risk index: 0.14, p = 0.038; Framingham risk score: 0.65, p = 0.041) also showed improvement. Serum adiponectin and thyroid-stimulating hormone levels were directly correlated with insulin resistance and cardiovascular risk scores. Conclusion The reduced serum adiponectin level and increased cardiovascular risk in clinical hypothyroidism were improved with hormone replacement, and serum adiponectin level was found to be a good prognostic marker for the treatment response.