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

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

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.

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).

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