A study suggests that there is a relationship between vitamin D levels and breast cancer growth and spread.
In this relatively small study, compared to women who had sufficient vitamin D levels, women who had the lowest levels of vitamin D were:
- 95% more likely to have breast cancer spread
- 73% more likely to have died as a result of breast cancer
Other research has found a similar link between vitamin D levels and prostate and colon cancer.
In this study, researchers found that only about 25% of the women in the study had adequate vitamin D levels when they were diagnosed with breast cancer.
Why low vitamin D levels are linked to breast cancer spread isn't clear. It's possible that having enough vitamin D influences how breast cancer behaves, so when vitamin D levels are low the breast cancer is more aggressive, harder to treat, and more likely to spread. It's also possible that low vitamin D levels are the result of other factors, such as diet, exercise, and lifestyle choices that directly affect breast cancer risk and prognosis. Some of the results suggest this might be happening. Women with lower vitamin D levels in this study were more likely to:
- be diagnosed with breast cancer before menopause
- be overweight
- to have high insulin levels
- be diagnosed with more aggressive forms of breast cancer
All of these factors are associated with a breast cancer prognosis that's worse than average.
Getting enough vitamin D, as well as calcium, is important for your overall good health -- especially the health of your bones. This study suggests that getting enough vitamin D also might be important if you're being treated for breast cancer.
But it's very important to remember that taking extra vitamin D based on the results of this relatively small study is not a good idea. Taking too much vitamin D can be harmful. Vitamin D supplements should be taken ONLY when your vitamin D level is too low.
If you're being treated for breast cancer, you might want to talk to your doctor about the results of this study. Ask whether checking your vitamin D level makes sense for your unique situation. 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.