Vitamin D is often in the news because most Americans get too little of it…and because deficiencies are associated with increased risk for cardiovascular disease, diabetes, Alzheimer’s disease, osteoporosis and many other serious health problems. And now here we go again—because too-low levels of that same vitamin are linked to nearly double the risk of dying from breast cancer, a new study shows.

Here’s what you (or the woman you love) should know…


Many studies have looked at the association between vitamin D levels and the risk of developing breast cancer, but there has been little exploration of the link between vitamin D and the odds of surviving breast cancer. To address that oversight, researchers looked for studies that investigated a link between breast cancer survival and levels of a vitamin D precursor called 25-hydroxyvitamin D, or 25(OH)D for short. The blood test for 25(OH)D is considered the most accurate way to measure how much vitamin D is in a person’s body.

Five studies met the researchers’ criteria, but their results varied. However, when the researchers pooled the data from these studies and did a statistical analysis, they found that…

  • Breast cancer patients with higher levels of 25(OH)D at the time of their diagnoses had a substantially lower risk of dying from their disease during the study periods, which averaged about 10 years.
  • Women with the highest levels, around 30 nanograms per milliliter (ng/mL), had a 44% lower risk of dying from breast cancer than women with the lowest levels, around 17 ng/mL.
  • There was a strong dose-related response, meaning that higher vitamin D levels were consistently associated with reduced mortality risk.



It’s important to point out that this study does not prove that 25(OH)D actually helps protect against death from breast cancer. It could be the other way around—the more deadly forms of breast cancer might cause vitamin D to become depleted, making 25(OH)D a marker for disease severity. However, the researchers consider this unlikely because no other studies suggest that cancer reduces 25(OH)D levels. Furthermore, the evidence in support of vitamin D’s protective mechanism is bolstered by the fact that cancer death rates are lower in areas of the US (and the world) with ample sunlight, the most abundant catalyst for naturally sufficient vitamin D levels.

Just how might higher 25(OH)D improve survival for cancer patients? Perhaps by the same mechanism through which it is thought to help prevent cancer in the first place. Lab studies have shown that vitamin D by-products interfere with cancer during three critical phases of development—by helping to maintain cell differentiation (well-differentiated cancer cells look more like normal cells and tend to grow and spread more slowly than poorly differentiated cells)…promoting apoptosis (normal programmed cell death)…and inhibiting angiogenesis (formation of blood vessels) that would feed tumors. It’s also possible that restoring 25(OH)D to normal levels may increase the function of E-cadherin, a protein that helps cells stick together to form organized tissue and suppress tumor growth.

Don’t DIY with D: The average blood level of 25(OH)D for breast cancer patients in the US is 17 ng/mL—which is too low. The researchers stated that blood levels “in all patients with breast cancer should be restored to the normal range [of] 30 to 80 ng/mL.” However, it’s important for cancer patients—and everyone else who wants to protect his or her health by optimizing vitamin D levels—to not take a do-it-yourself approach. As we’ve been warning you for several years, too much vitamin D can be dangerous, increasing the risk for blood vessel calcification, heart rhythm abnormalities and kidney damage. Prudent: Ask a nutrition-oriented doctor to check your 25(OH)D level and, if necessary, to prescribe an appropriate dosage for supplementation.

For much more info on breast cancer: Read Breast Cancer Guide: Prevent, Detect, Treat, Recover.