What is the Connection Between Vitamin D and Breast Cancer?

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  • Written By: Kaitlyn N. Watkins
  • Edited By: A. Joseph
  • Last Modified Date: 10 October 2018
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Out of the many different types of cancer affecting women, breast cancer is the most prevalent, and it affects more than 1 million women every year. Researchers continue to study factors that might prevent or treat this overwhelming illness, including the link between vitamin D and breast cancer. More studies are needed to determine whether vitamin D can be used successfully to prevent breast cancer, but there is evidence to suggest that it can be helpful in treating breast cancer.

Vitamin D is actually not a vitamin but a group of fat-soluble prohormones. Humans acquire vitamin D through the absorption of sunlight, which is why deficiencies are more likely to occur during the winter months, when people are less likely to be outside and more likely to wear more clothing. A small amount of vitamin D can be obtained naturally through certain foods such as fatty fish and eggs, but more common sources of vitamin D are fortified foods such as milk, juices, breads and cereals.

The positive effects of vitamin D on the body include improving immune function, reducing inflammation, improving muscle strength and aiding in the absorption of calcium, which is why calcium-rich foods are frequently fortified with vitamin D. Dietary supplements are also available, but the risk of toxic levels of vitamin D increases with excessive supplement intake. A vitamin D overdose can lead to heart problems, reduced mental function, pain, fever, thirst, vomiting and weight loss.


Calcitrol, the most active form of vitamin D, has been found to help reduce the growth of breast cancer cells. This is positive news for linking vitamin D and breast cancer treatment, because it promotes cancer cell death and blocks cancer-growing substances from sending signals to the cells. It has been found that treating breast cancer patients who have a vitamin D deficiency might increase the vitamin D receptors in the body, thus leading to slower tumor growth and longer remission.

It is not clear how vitamin D can play a definitive role in breast cancer prevention. One study found that calcium and vitamin D supplements had no more effect on the risk of breast cancer than did placebo supplements. Studies on postmenopausal women have also found no substantive link between vitamin D and breast cancer prevention.

There has been evidence that supplements that include vitamin D can reduce the risk of cancer in postmenopausal women, but these studies primarily focused on bone loss, not cancer. It was unclear whether vitamin D was a determining factor in the cancer prevention, and the study did not link vitamin D and breast cancer, specifically. There has been optimism about the link between vitamin D and breast cancer, but it appears that cancer cells must exist in the first place before the positive effects can take place. More information is needed to determine the significance of vitamin D and breast cancer prevention, but because of its ability to slow and kill existing cancer cells, vitamin D could become an important part of breast cancer treatment.



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