Vitamin D Deficiency Fuels Aggressive Breast Cancer in Mice

Breast tumours in mice deficient in vitamin D grow faster and are more likely to metastasize than tumours in mice with adequate levels of vitamin D, according to a study at the Stanford University School of Medicine.

The research highlights a direct link between circulating vitamin D levels and the expression of a gene called ID1, known to be associated with tumour growth and breast cancer metastasis.

Previous studies have suggested that low levels of vitamin D not only increase a person’s risk of developing breast cancer, but are also correlated with more aggressive tumours and worse prognoses.

Vitamin D has long been known to be essential for calcium absorption and bone health. More recently, however, researchers have begun to suspect that vitamin D may affect many other important biological processes, including tumour progression. However, it’s not clear exactly which step in cancer development the vitamin may affect.

Although the new research was conducted primarily in mice and on mouse cells, the researchers found in a study of 34 breast cancer patients that vitamin D is directly linked with the expression of the ID1 gene in a human breast cancer cell line.

“Although much more research needs to be done, research from our lab and others suggests that people at risk for breast cancer should know their vitamin D levels and take steps to correct any deficiencies,” said Dr. Brian Feldman, senior author of the study published this week in the journal Endocrinology.

The researchers emphasize that their findings don’t imply that more vitamin D is always better. Correcting a deficiency is very different from taking more than the recommended dosage.

Osteoporosis Canada recommends daily supplements of 400 to 1000 IU for adults under age 50 without osteoporosis or conditions affecting vitamin D absorption. For adults over 50, supplements of between 800 and 2000 IU are recommended.

Excess levels, variously estimated to occur at about 4,000 to 10,000 IU per day, have been linked to damage to the kidneys, cardiovascular system and other organs.

Not all medical organizations agree on the optimal amount of vitamin D.

The confusion stems in part from the fact that, although it can be ingested via food and nutritional supplements, our bodies can also make vitamin D with the help of ultraviolet rays from the sun. So it’s difficult to know exactly how much any individual may need to take as a supplement, and that amount can vary throughout the year. Those who don’t get enough sun exposure, or people with darker skin, are more likely than fair-skinned individuals who spend time outdoors each day to be deficient.

In this study, mouse breast cancer cells were implanted into the mammary fat pad of laboratory mice.

“Our study shows that a deficiency in vitamin D levels, or an inability of tumour cells to respond appropriately to the presence of vitamin D, is sufficient to trigger non-metastatic cancer cells to become metastatic,” said Feldman.