October is Breast Cancer Awareness Month, and individuals worldwide are spreading information, honoring those affected by the disease and wearing pink in support of this cause. One key point of Breast Cancer Awareness Month is to educate women on how they can decrease their risk of breast cancer.
The pathology of breast cancer is still unknown, but there are several risk factors that have been associated with this disease. These risk factors include, but are not limited to, age, start of menopause, hormone therapy, family history and oral contraceptive use. Additionally, past research has linked breast cancer risk and survival rates to vitamin D status. However, there has been limited research evaluating the relationship between vitamin D status and prognosis of breast cancer. Therefore, researchers from this study evaluated the effect of vitamin D status on severity of cancer prognosis in a high-risk group of postmenopausal women.
A total of 192 postmenopausal Brazilian women between the ages of 45 and 75 were included in this cross-sectional study. All of the participants attended the Breast Disease Assessment Center of the University Hospital in Southeastern Brazil during 2015-2016. The researchers collected the following data: age, menopausal age, time since menopause, age of first gestation, duration of breastfeeding, current smoking, prior use of hormone therapy, history of chronic diseases, family history of breast cancer and use of medications.
They also measured the patient’s anthropometric data and serum vitamin D levels just following breast cancer diagnosis and prior to medical treatment. Due to the fact that breast cancer prognosis is widely variable, the researchers evaluated several markers that contribute to disease outcome, including:
- Tumor grade: (1) well differentiated, (2) moderately differentiated, and (3) undifferentiated. While grade 1 tumor cells may look similar to surrounding healthy cells, grade 3 tumors are undifferentiated, or made up of only cancerous cells. This indicates disease progression.
- Tumor stage: measured by a scale of 1-3; (1) localized invasive breast cancer, (2) inoperable locally advanced invasive breast cancer, and (3) metastatic disease. While localized breast cancer remains within the affected body tissues, metastatic cancer migrates to other parts of the body.
- Lymph node presence: positive if at least one lymph node were identified as having breast cancer metastasis. This means that the cancer has spread beyond the breast tissue to the rest of the body.
- Hormone-receptor status: presence or absence of estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2) and cell proliferation index (Ki-67) status. Positive scores for ER and PR receptors mean that the cancer cells will grow in response to estrogen or progesterone, while positive scores for HER2 and Ki-67 indicate increased tumor growth.
This is what the researchers found:
- Average vitamin D status was 25.8 ng/ml (64.5 nmol/l).
- Of the total participants, 33.9% were considered to be vitamin D sufficient (>30 ng/ml; >75 nmol/l), 47.9% were considered insufficient (20-30 ng/ml; 50-75 nmol/l) and 18.2% were considered vitamin D deficient (<20 ng/ml; 50 nmol/l).
- Insufficient and deficient 25(OH)D levels were associated with increased tumor grade, locally advanced and metastatic disease, more positive lymph nodes, a lower proportion of ER, PR-positive tumors and higher Ki-67 indices.
- Vitamin D status was not significantly associated with tumor size, histology of breast cancer or HER2 status.
The researchers concluded:
“In conclusion, in Brazilian postmenopausal women with breast cancer, there was an association between vitamin D insufficiency or deficiency and tumors with worse prognostic features. Low vitamin D levels were shown to be a risk factor for estrogen receptor-negative tumors, positive axillary lymph node status and a higher rate of cell proliferation.”
As always, it is important to note the study’s strengths and limitations. Strengths of this study include the large sample size and the fact that researchers checked vitamin D levels so soon after breast cancer diagnosis. However, there were some limitations that should be addressed. Due to the cross-sectional study design, researchers were unable to measure vitamin D status over time, nor were they able to prove a causal relationship exists between vitamin D status and breast cancer prognosis. Also, vitamin D status was only measured once. Vitamin D levels should be measured over time in future studies to determine if chronic vitamin D deficiency is associated with worse outcomes in breast cancer patients.
Due to lack of vitamin D within the diet, individuals looking to increase their vitamin D status should spend time outside when their shadow is shorter than they are tall or supplement with at least 5,000 IU daily (125 ug).
If you have any questions about vitamin D supplementation, sun exposure or the relationship between vitamin D and breast cancer, please contact us at [email protected].
Peterson, R. & Cannell, JJ. Researchers discover worse breast cancer outcomes are associated with vitamin D deficiency. The Vitamin D Council Blog & Newsletter, 10/2017.