Vitamin D & Breast Cancer

by Dr. Sophia Guerra ND

Not only is vitamin D necessary for normal bone calcification, but this vitamin is closely related to the body’s stress hormone, cortisol, and estrogen. It is also essential for a healthy immune system, nervous system development, heart function and normal blood clotting. Now vitamin D has another reason to tout its horn! Recent studies out of Stanford University are suggesting that dietary vitamin D and calcitriol, the hormonally active form of vitamin D, could have a significant role in the prevention and treatment of breast cancer, specifically in cases where the cancer cells have receptors for estrogen (ER+BCa).

Vitamin D3 or Calcitriol exerts it’s anti-cancer effects by stopping cancer cell development, stimulating cellular self-destruction, inhibiting metastasis, tissue invasion and angiogenesis (the formation blood vessels that feed cancer cells or tumors). Calcitriol seems to exert its most clinically relevant effect by directly binding to and inhibiting the growth of estrogen receptor positive cancer cells.

Breast cancer cells that have receptors for estrogen (ER+BCa) are stimulated to grow in response to circulating estrogen.  Women who have been diagnosed with ER+BCa respond well to hormonal therapies that try to decrease the amount of circulating estrogen in your body or block estrogen from binding to the cells. Vitamin D3 seems to be doing exactly that! It decreases the activity of an enzyme called, aromatase, responsible for estrogen synthesis locally in the breast fatty tissue. It also decreases the number of estrogen receptors on ER+BCa cells.  Now if that wasn’t enough already, vitamin D3 also decreases the amount of inflammatory molecules called prostaglandins (PGs) in the breast tissue, which decreases aromatase activity and estrogen production too!

The good news is that the vitamin D found in food is thought to exhibit similar anti-cancer activity because breast tissue has a built-in enzyme that converts dietary vitamin D into its hormonally active form, calcitriol or vitamin D3. Supplementing with vitamin D3 will ensure adequate amounts of active vitamin D reach the breast tissue. Research by the Ontario Community Laboratory found that only 38-54% of Canadians had “sufficient” vitamin D3 (75 – 250 nmol/L). I recommend getting your vitamin D3 status tested with a routine blood test to help determine the appropriate dose of vitamin D3, which can range from 1000-4000IU. The best food sources of vitamin D include cod liver oil, which provides a whopping 1300IU per tablespoon, dairy products, sardines, liver, and eggs.