Correlation Between Serum Vitamin D3 Levels and Thyroid Function Tests (Free T3, Free T4, TSH) in an Indian Population: A Cross-Sectional Study

Background: Vitamin D deficiency and thyroid disorders are common in the Indian population. Emerging evidence suggests a possible association between Vitamin D status and thyroid function. The objective is to evaluate the correlation between serum Vitamin D3 levels and thyroid function parameters (FT3, FT4, TSH). Material and Methods: A cross-sectional study was conducted using biochemical data of 200 patients attending medicine OPD and admitted in Government Medical College Dungarpur Hospital (Haridev Joshi Hospital Dungarpur). Serum Vitamin D3, Free T3 (FT3), Free T4 (FT4), and TSH levels were analyzed. Pearson correlation and regression analysis were performed. Results: Mean Vitamin D3 level was 19.5 ± 8.2 ng/mL. A mild negative correlation was observed between Vitamin D3 and TSH (r ≈ -0.12), while weak positive correlations were noted with FT3 (r ≈ +0.15) and FT4 (r ≈ +0.10). Patients with severe Vitamin D deficiency showed higher TSH levels suggestive of subclinical hypothyroidism. Conclusion: Vitamin D deficiency may be associated with altered thyroid function, particularly elevated TSH levels. Screening for Vitamin D deficiency in patients with thyroid disorders may be beneficial.

Keywords: Vitamin D3, Thyroid function, TSH, FT3, FT4, India, Cross-sectional study.