Evaluation of vitamin D levels in patients with primary hypothyroidism: A cross-sectional study

Background: Vitamin D deficiency (VDD) and hypothyroidism have been linked in research with inconsistent outcomes. Because of the controversy surrounding these two disorders and their relatively high incidence, we undertook a case-control research comparing the prevalence of VDD in hypothyroid patients (both TPO-Ab positive and negative) to euthyroid controls. Materials and Methods: This is a cross-sectional study with a single centre. Adults (aged 18 and above) of both sexes with primary hypothyroidism (TSH >5.1 mIU/L) were included (n = 165), as were age and sex matched euthyroid (TSH 5 mIU/ml) controls (n = 165) from the outpatients' department. Biochemical parameters like Thyroid stimulating hormone (TSH), free T4 (fT4), 25 hydroxy vitamin D (Vit D) and thyroid peroxidase antibody (TPO-Ab) were tested in both the groups. Results: The study involved 330 patients, with 165 (mean age 46± 15 years) having primary hypothyroidism (3 having subclinical hypothyroidism) and 165 (mean age 45± 17 years) being euthyroid controls. VDD was seen in 96 percent of hypothyroid patients compared to 90 percent in the control group. The hypothyroid group had a significantly lower mean Vitamin D level than the euthyroid group (12.03± 8.6 SD vs. 17.49± 11.89 SD [ng/ml]; P= 0.001). TPO-Ab was found in two-thirds of the hypothyroid group (110/165). The mean Vitamin D level in the TPO-Ab positive hypothyroid group was 10.4± 7.2 ng/ml, compared to 15.3± 10.3 ng/ml in the TPO-Ab negative group (P = 0.004). With increased TPO-Ab titers, there was a downward trend in Vitamin D levels. A direct association between Vitamin D levels and TPO-Ab, on the other hand, did not reveal any relevance. Conclusion: Patients with hypothyroidism had considerably lower vitamin D levels than euthyroid controls. TPO-Ab positive individuals had lower vitamin D levels than TPO-Ab negative patients.   Keywords: Euthyroid, Hypothyroidism, Primary hypothyroidism, Vitamin D deficiency.