Background: Vitamin D, classically involved in calcium homeostasis, has garnered recent interest for its potential role in cancer prevention and therapy. Although few risk factors have been established in the development of well-differentiated thyroid carcinoma, some would argue that no clear modifiable risk factor exists. Our study is one of the first to explore the relationship between vitamin D deficiency and thyroid cancer.
Methods: This retrospective cohort study was done at a university-affiliated thyroid cancer centre. In 2010, 212 patients undergoing thyroidectomy had their preoperative 25-hydroxyvitamin D(3) levels recorded in addition to the final pathologies of their resected thyroid nodule. The patients were stratified based on vitamin D status; vitamin D deficiency (VDD), reflecting levels under the established threshold of 37.5 nmol/L; and vitamin D sufficiency (VDS), reflecting levels above it. The primary outcome of malignancy rate was used to compare the proportion of malignant nodules in the VDD versus the VDS groups.
Results: The malignancy rate rises when comparing the VDS and VDD groups, from 37.5 (33 of 88) to 75% (9 of 12), respectively, corresponding to a relative risk of 2.0 (p = .03, 95% CI 1.07-2.66).
Conclusion: This is the first study to demonstrate the inverse relationship between VDD and well-differentiated thyroid carcinoma. Larger prospective studies are needed to replicate these results. Should this happen, VDD may be the first modifiable risk factor for thyroid cancer.