Is Vitamin D Deficiency a Risk Factor for Thyroid Cancer?

March 18, 2019
Naveed Saleh, MD, MS
Naveed Saleh, MD, MS

A meta-analysis looked at the controversial link between decreased serum 25-hydroxyvitamin D levels and incidence of thyroid cancer.

Decreased serum 25-hydroxyvitamin D levels were linked to a higher risk of thyroid cancer, and vitamin D deficiency may be a risk factor for developing thyroid cancer, found a recent meta-analysis published in the journal Nutrition.

Zhao et al searched databases, including PubMed, the Cochrane Library, Sinomed, the China National Knowledge Infrastructure, Wanfang Data, and clinical trial register centers, for case-control studies focusing on vitamin D in thyroid cancer. A total of 14 articles were identified and included in the meta-analysis.

Researchers found that levels of serum 25-hydroxyvitamin D were lower in preoperative thyroid cancer patients vs controls (−0.22; 95% CI, −0.36 to −0.09; P = .001). Post-thyroidectomy, no difference in thyroid levels were noted between groups (−0.19; 95% CI, −0.47 to 0.10; P = .21). The pooled odds ratio of vitamin D deficiency and thyroid cancer based on six studies was 1.30 (95% CI, 1.00–1.69; P = .05).

The frequency of thyroid cancer-particularly papillary thyroid cancer-has been on the rise globally. Some experts hypothesize that this increased incidence is due to better imaging techniques or screening, which could lead to overdiagnosis and unnecessary medical treatment. However, this explanation does not account for the rising incidence of non-microcarcinoma of the thyroid.

In light of this increased prevalence of thyroid cancer, experts have examined risk factors for thyroid cancer, including sex, age, family history, and mutations, which cannot be prevented.

Emerging thyroid cancer research has focused on risk factors that can be modified, such as obesity, insulin resistance, nutrition, and vitamin D deficiency. Of note, serum 25-hydroxyvitamin D is the principal circulating form of vitamin D representing reserve levels. This form of vitamin D takes part in phosphorous and calcium metabolism, as well as cell differentiation and proliferation.

To date, results from studies examining the association between vitamin D levels and thyroid cancer have been mixed. Some studies have suggested a protective effect, whereas others studies have indicated that higher levels of vitamin D are linked to thyroid cancer in patients with lymph node metastases.

One limitation of the current study is that measurement methods for 25-hydroxyvitamin D varied from study to study. Furthermore, they included various types of thyroid cancer, with the association between vitamin D and various pathological types unable to be determined on subgroup analysis.

“Although vitamin D deficiency may act as a risk factor for thyroid cancer, the difference of serum 25-OHD [25-hydroxyvitamin D] in different pathological characteristics in patients with thyroid cancer cannot be concluded from these limited studies,” concluded the authors. “Therefore, more prospective clinical studies with larger sample sizes may strengthen the evidence. More experimental studies should be done to elucidate the mechanism of vitamin D deficiency related to thyroid cancer.”