Vitamin D deficiency and thyroid cancer: is there a true association? A prospective observational study.

Introduction: Literature data indicate a correlation between vitamin D deficiency and thyroid cancer (TC). We conducted this observational study to test this hypothesis.

Methods: We studied 327 consecutive thyroidectomy cases, and compared patients with TC and those who had benign thyroid disease (BTD). In total, 183 cases with well-differentiated TC (group B) were compared with 144 cases of BTD (group A). We defined 25-hydroxyvitamin D (25(OH)VitD) values <10ng/ml as severe vitamin D deficiency (15.4%), 10-30ng/ml as inadequacy (70.4%) and >30ng/ml as adequate (14.2%). We further used a cut-off point of 30ng/ml (used in a recent meta-analysis) to classify patients as vitamin D deficient or not.

Results: There was no statistically significant difference in the following: age, size of the thyroid gland, preoperative calcium levels, preoperative parathormone and vitamin D levels, body mass index and anti-thyroid antibodies. Only thyroid-stimulating hormone and weight of the thyroid gland were found to differ. There was no significant difference in mean vitamin D levels (group A = 19.82ng/ml [sd 9.59] vs group B = 19.69ng/ml [sd 11.34]; p = 0.917). The same was found when we compared the two groups according to the three categories of vitamin D values (deficiency, inadequacy, adequacy; p = 0.485) and when we performed the analysis based on all threshold levels (10, 20 and 30ng/ml; p = 0.328). Using various statistical methods, no correlation was found between vitamin D deficiency and differentiated TC (overall, microcarcinomas, macrocarcinomas).

Conclusions: Based on our results, no correlation between vitamin D deficiency and TC was confirmed, contradicting and questioning the results of two recent meta-analyses.