Scientific Evidence on Interrelationship Between Vitamin D and Vitamin B12 in Euthyroid Subjects

Abstract

Introduction: Vitamin B12 acts as the coenzyme of homocysteine methyl transferase which converts homocysteine (Hcy) to methionine and thyroxine regulates the activity of this enzyme. Vitamin D modulates the gene expression of enzymes involved in Hcy metabolism. Vitamin D receptors are present on thyrotropes that secrete TSH speculating the link between vitamin D and thyroid gland activity.

Objective: The study aims to explore the correlation between vitamin D and B12 with thyroid hormones in euthyroid status.

Methods: 100 euthyroid subjects aged between 20-60 years, with normal thyroid hormones and TSH, were classified into two groups based on vitamin B12 levels. Group I consisted of 50 patients whose vitamin B12 level was less than 200 pg/ml (B12 deficient group) and Group II included 50 patients whose vitamin B12 level was more than 200 pg/ml (B12 sufficient group). Thyroid profile, total vitamin D, vitamin B12 and folic acid were determined in the fasting serum samples by ECLIA in Cobas 6000 autoanalyzer.  

Results: There was an apparent decrease in mean serum TSH, T3 and T4 levels in vitamin B12 deficient group compared to sufficient group. A significantly higher vitamin D was observed in vitamin B12 sufficient group than the deficient group (p = 0.001). Vitamin D and B12 showed positive correlation with serum T3, T4 and TSH. The correlation between TSH and vitamin B12 (r = 0.31, p = 0.01), vitamin D (r = 0.435, p = 0.001) were significant.  Further, the correlation between vitamin D and B12 (r = 0.42, p = 0.005), was also statistically significant.

Conclusions: Vitamin B12 deficiency is linked to vitamin D deficiency which in turn may be associated with alteration of thyroid profile even in euthyroid status. The study establishes a link between vitamin B12 and vitamin D in euthyroid subjects.