Investigating the effect of levothyroxine replacement on cholesterol levels in hypothyroid patients

Effects of levothyroxine therapy on the lipid profile of hypothyroid patients lead to decrease in the risk of cardiovascular diseases and mortality.

Overt or subclinical hypothyroid dysfunction has negative effects on lipid metabolism and leads to hypercholesterolemia that in turn increases the risk of cardiovascular diseases and mortality. In this matter, several interventional studies investigated the effects of levothyroxine therapy on the lipid profile of hypothyroid patients, and conflicting results have been obtained. The current research aims to investigate the effect of levothyroxine replacement on cholesterol levels in hypothyroid patients.

The present prospective study examined 112 patients (mean age of 43.80 ± 14.36 years) with overt hypothyroidism. To do so, 72.3% of patients were females. Levothyroxine replacement therapy was prescribed for patients, and they were examined monthly to evaluate the effects of therapy on their lipid profiles. After reaching normal thyroid stimulating hormone (TSH), the patients' laboratory parameters, including TSH, total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides, were surveyed.

After Levothyroxine therapy, there was a significant reduction in mean TSH (62.03 vs. 2.33 ± 1.95; P < 0.0001), triglycerides (145.57 ± 88.65 vs. 121.91 ± 59.52, P = 0.002), cholesterol (203.90 ± 53.73 vs. 166.65 ± 40.07, P < 0.0001), and serum LDL (123.61 ± 45.03 vs. 95.99 ± 24.20, P < 0.0001), but the mean value of serum HDL did not show any significant change (54.18 ± 16.60 vs. 51.59 ± 18.38, P = 0.274).

Levothyroxine therapy has beneficial effects on lipid profile in patients with overt hypothyroidism because it decreases serum triglyceride, total cholesterol, and LDL. However, levothyroxine therapy does not significantly change HDL levels.