A small study suggests a link between vitamin D levels and breast cancer growth and spread. Women diagnosed with more aggressive breast cancer or advanced-stage breast cancer were more likely to have low vitamin D levels than women diagnosed with less aggressive or early-stage breast cancer. These results were presented the American Association of Cancer Research (AACR) Conference on the Science of Cancer Health Disparities.
The researchers looked at blood samples to figure out the vitamin D levels of 107 women who had been diagnosed with breast cancer in the previous 5 years. Each woman's vitamin D level was compared to the stage and other characteristics of the breast cancer at diagnosis.
Compared to women with normal vitamin D levels, women who had low vitamin D levels were more than 8 times more likely to have been diagnosed initially with cancer that had spread beyond the breast, either to the skin or chest wall (regional spread) or to parts of the body away from the breast (distant/metastatic spread).
Vitamin D levels were lowest in women diagnosed with triple-negative breast cancer. Triple-negative breast cancer is estrogen-receptor-negative, progesterone-receptor-negative, and HER2-negative. Triple-negative breast cancers are usually more aggressive, harder to treat, and more likely to come back (recur) than cancers that are hormone-receptor-positive or HER2-positive.
In this study, African American women were more likely to have low or severely low vitamin D levels:
- 60% of African American women (36 women) had some vitamin D deficiency
- 15% of white women (seven women) had some vitamin D deficiency
- only 21.7% of African American women (13 women) had adequate vitamin D levels
- 43% of white women (20 women) had adequate vitamin D levels
- 17% of African American women (six women) had severe vitamin D deficiency compared to none of the white women
Vitamin D is mostly produced in the skin when you're in the sun. It's possible that the African American women had low vitamin D levels because of darker skin color, which can lower vitamin D production.
Other research also has suggested a link between low vitamin D levels and the development and spread of breast cancer. It's not clear how or why vitamin D levels affect breast cancer spread. It may be that adequate vitamin D levels affect how breast cancer behaves; so when vitamin D levels are low, breast cancer is more likely to develop and if it does develop, it's more aggressive, harder to treat, and more likely to spread. It's also possible that low vitamin D levels are caused by other factors, such as diet, exercise, and lifestyle choices that also affect breast cancer risk and prognosis.
Getting enough vitamin D, as well as calcium, is important for your overall good health -- especially the health of your bones. This study and other research suggest that getting enough vitamin D also might be important if you're being treated for breast cancer. Still, more research is needed to better understand the link between vitamin D and breast cancer. Checking vitamin D levels as part of routine healthcare might make sense. The researchers who did this study DON'T advise routinely taking vitamin D supplements. Taking too much vitamin D can be harmful. Vitamin D supplements should be taken only when a blood test shows your vitamin D level is low.
If you're being treated for breast cancer, you might want to talk to your doctor about the results of this study. Ask if checking your vitamin D level makes sense for you. If it's low, you and your doctor can decide if a vitamin D supplement is right for you.
To learn more about dietary supplements, visit the Well-Known Supplements page in the Breastcancer.org Nutrition section.