Researchers recently published a study in the journal Thyroid which indicated vitamin D’s relationship to various clinical markers in women with papillary thyroid cancer.
Papillary thyroid cancer (PTC) is the most common form of thyroid cancer, a type of cancer that occurs in the cells of the thyroid gland in the neck. PTC makes up 75-85% of all thyroid cancers with around 60,000 new cases diagnosed in the United States each year.
The cause of PTC is not well understood, but research suggests that both genetic and environmental factors play a role.
Vitamin D’s suggested role in a variety of other cancers led researchers to determine if and how vitamin D relates to PTC. However, research on this subject is limited to a few small studies that suggest low vitamin D levels relate to the incidence of PTC.
Recently, researchers at Pusan National University in South Korea aimed to take this research a step further and determine if vitamin D played a role in specific markers of PTC and therefore may be clinically relevant in improving aspects of PTC.
They recruited 548 female patients between the ages of 15 and 80 years old who were about to undergo thyroidectomy. They chose to exclude male patients because PTC is more common among women.
The researchers used the American Joint Committee on Cancer’s (AJCC) tumor, lymph node, and metastasis (LNM) classification to define the clinical markers of PTC. The AJCC is an organization that helps classify and define cancer staging standards.
For tumor size (T), the researchers compared T1/T2 versus T3/T4. T1 and T2 represent tumors at or less than 4 cm and only present in the thyroid. T3 and T4 represent tumors greater than 4 cm only present in the thyroid or extending to nearby tissues such as the larynx or trachea.
The researchers looked at whether there was regional metastasis or not in the lymph node (LNM or no LNM), or if there was lateral LNM (metastasis of the cancer to other areas of the neck). The researchers also classified tumor stage as stage 1 or 2 versus stage 3 or 4.
All patients had their vitamin D levels measured two weeks before surgery. The researchers categorized the women into four groups depending on their vitamin D level:
- Group 1: 3.91 – 13.62 ng/ml
- Group 2: 13.70 – 18.52 ng/ml
- Group 3: 18.57 – 26.23 ng/ml
- Group 4: 26.26 – 59.31 ng/ml
The researchers were interested in if lower vitamin D levels related to worse outcomes in the clinical markers. They also were interested in how the markers differed between women who had levels below the median of 18.5 ng/ml compared to those with higher levels.
Here’s what the researchers found:
- Vitamin D levels were significantly higher in women younger than 45 years old and with a tumor size of less than 1 cm.
- A linear trend was observed between decreasing vitamin D levels and increasing tumor size (P = 0.014).
- Increasing vitamin D levels were related to decreased LNM in patients experiencing metastasis (P = 0.014).
- In an adjusted analysis, group 2 had an 89% increased risk for T3 and T4 (P = 0.026), a two times higher risk for LNM (P = 0.009), and a 5 times increased risk for lateral LNM (P = 0.004) compared to group 4.
- LNM was the only marker with a significantly increased risk when comparing group 1 with group 4.
In comparing women below or above the median vitamin D level of 18.5 ng/ml, the researchers found that lower vitamin D levels were independently associated with a significant 69% increased risk for LNM, 3 times increased risk for LNM, and 60% increased risk for stage 3 and 4 cancer compared to those above the median.
The researchers stated,
“In conclusion, lower preoperative serum [vitamin D levels] appears to be associated with poor clinicopathologic features with respect to PTC in female patients. Vitamin D insufficiency may be a modifiable risk factor for PTC.”
The researchers state that their study population of only Asian women limits the ability to generalize their results to other populations living at different latitudes. Furthermore, the observational design of the study means we cannot say for certain that low vitamin D levels lead to worse disease outcomes in PTC.
Thyroid cancer is a relatively rare cancer, and these results support the hypothesis that vitamin D plays a general role in cancer through a variety of mechanisms.
To validate and confirm these results, vitamin D supplementation prior to PTC diagnosis or during treatment will confirm if vitamin D reduces risk or helps manage aspects of this disease.