Association of Serum Vitamin D Levels with Hypothyroidism: A Clinical Correlation Study

Abstract

Background: Hypothyroidism is a prevalent endocrine disorder affecting approximately 10.95% of the Indian population. Recent evidence suggests potential associations between vitamin D deficiency and thyroid dysfunction, particularly in autoimmune thyroid conditions. However, the relationship between vitamin D status and primary hypothyroidism remains incompletely understood.

Objective: To investigate the association between serum vitamin D concentrations with primary hypothyroidism, as well as to assess the interrelation of vitamin D status with thyroid functional indices.

Methods: This cross-sectional analytical study was conducted at Dr DY Patil Medical College, Nerul, Navi Mumbai, from December 2023 to December 2024. A total of 130 participants were recruited using consecutive sampling, including patients with hypothyroidism and euthyroid controls. Serum thyroid-stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), anti-thyroid peroxidase (anti-TPO) antibodies, and 25-hydroxyvitamin D levels were measured using chemiluminescent immunoassays. Vitamin D status was classified as deficiency (<20 ng/ml), insufficiency (20-30 ng/ml), and sufficiency (>30 ng/ml). Statistical analysis included correlation analysis and multiple linear regression.

Results: Hypothyroid patients demonstrated significantly lower mean vitamin D levels (14.9 ± 8.2 ng/ml) compared to euthyroid individuals (21.3 ± 9.8 ng/ml, p<0.001). Vitamin D deficiency prevalence was substantially higher in hypothyroid patients (77.8%) versus euthyroid participants (55.3%, p=0.012). A significant negative correlation was observed between vitamin D levels and TSH (r = -0.342, p<0.001), with positive correlations noted for free T4 and T3. Anti-TPO antibody positivity was significantly higher in hypothyroid patients (55.6%) compared to euthyroid individuals (10.5%, p<0.001). Multiple regression analysis identified TSH as an independent predictor of vitamin D levels.

Conclusion: This study demonstrates a significant inverse association between serum vitamin D levels and hypothyroidism, with a dose-response relationship across thyroid dysfunction severity. The findings suggest that vitamin D deficiency may contribute to hypothyroidism pathogenesis and support the consideration of vitamin D screening and supplementation in hypothyroid patients