The unseen impact of subclinical hypothyroidism on lipid profile and cardiovascular risk

Subclinical hypothyroidism (SCH), defined by elevated thyroid-stimulating hormone (TSH) with normal circulating thyroid hormones, is a common endocrine disorder that frequently remains clinically silent. Emerging evidence suggests that even mild thyroid dysfunction may influence lipid metabolism and contribute to early cardiovascular risk. However, the extent to which TSH levels reflect lipid abnormalities in SCH remains controversial.

This study aimed to evaluate the influence of SCH on lipid metabolism and to determine whether TSH levels are associated with alterations in lipid profile parameters and atherogenic cardiovascular risk markers.

A cross-sectional comparative study was conducted including 40 participants: 20 patients diagnosed with SCH and 20 euthyroid controls matched for demographic characteristics. Serum concentrations of TSH, free triiodothyronine (FT3), and free thyroxine (FT4) were measured alongside lipid profile parameters, including total cholesterol, triglycerides, low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C). The LDL/HDL ratio was calculated as an indicator of atherogenic cardiovascular risk. Independent sample t-tests were applied to compare study groups, and linear regression analysis was performed to evaluate associations between TSH levels and lipid parameters.

Individuals with SCH demonstrated significant lipid alterations compared with euthyroid controls. Triglyceride levels were significantly higher (165.7 ± 60.8 vs. 92.9 ± 39.8 mg/dL; p = 0.0136), while HDL-C levels were significantly lower (50.8 ± 12.4 vs. 58.6 ± 11.3 mg/dL; p = 0.0136). The LDL/HDL ratio was also significantly elevated in the SCH group (2.25 ± 1.05 vs. 1.57 ± 0.56; p = 0.0027), indicating a more atherogenic lipid profile. In contrast, total cholesterol and LDL-C showed modest but statistically non-significant increases. Regression analysis revealed weak and non-significant correlations between TSH levels and lipid parameters.

SCH is associated with unfavorable lipid alterations characterized by elevated triglycerides, reduced HDL-C, and an increased LDL/HDL ratio, suggesting early atherogenic risk despite normal thyroid hormone levels. These findings highlight the importance of comprehensive lipid assessment in SCH and suggest that the LDL/HDL ratio may serve as a more sensitive indicator of cardiovascular risk than TSH alone.