Vitamin D and Breast Cancer

Author: John Monczunski

Vitamin D has tantalized cancer researchers ever since the protein receptor for the vitamin was discovered in a wide array of bodily tissues about 15 years ago. For years its only known function was in maintaining healthy teeth and bones. So when scientists found the receptor in the breast and other bodily tissues, they were shocked.

“The question, obviously then, is what is it doing there?” says JoEllen Welsh. And, the second question, does it have any role in cancer? The professor of biological sciences has spent much of her career attempting to answer those questions. Thus far the answer to question one remains a work in progress, while the answer to question two is an optimistic “maybe.”

Studies in Welsh’s lab have shown that vitamin D will stop the growth of breast cancer cells and shrink tumors in mice. Despite that success, she cautions, “we can’t recommend that people take large doses of vitamin D because that could have an adverse effect on calcium in the bones.” Currently, several pharmaceutical companies are attempting to develop less toxic synthetic analogs to vitamin D.

Most recently Welsh and her colleagues have begun using genetic engineering techniques to learn vitamin D’s precise function in breast tissue. When the researchers examined mice lacking the gene for the vitamin D receptor, they found the mammary gland grew more than in normal mice. They also discovered that after lactation the gland did not shrink back to its normal state as completely as mice with the vitamin D receptor gene.

“This suggests to us that vitamin D receptors may be important in maintaining the normal cycling of the gland [through pregnancy and back to its state in nonpregnancy],” Welsh says. This is significant, the researcher points out, because the body normally “cleans out” defective, mutated cells during this cycling process, which may explain why pregnancy and lactation are known to lower a woman’s risk for breast cancer. Welsh’s group hypothesizes that the genetic defect for the vitamin D receptor could make someone more susceptible to breast cancer.

While Welsh’s interest is primarily in the role of vitamin D in breast tissue, she notes that other studies have suggested abnormalities in Vitamin D “signaling” may be implicated in leukemia, prostate cancer and colon cancer.

John Monczunski is an associate editor of this magazine.